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=============================
User Guide for AMDGPU Backend
=============================
.. contents::
:local:
Introduction
============
The AMDGPU backend provides ISA code generation for AMD GPUs, starting with the
R600 family up until the current GCN families. It lives in the
``lib/Target/AMDGPU`` directory.
LLVM
====
.. _amdgpu-target-triples:
Target Triples
--------------
Use the ``clang -target <Architecture>-<Vendor>-<OS>-<Environment>`` option to
specify the target triple:
.. table:: AMDGPU Target Triples
:name: amdgpu-target-triples-table
============ ======== ========= ===========
Architecture Vendor OS Environment
============ ======== ========= ===========
r600 amd <empty> <empty>
amdgcn amd <empty> <empty>
amdgcn amd amdhsa <empty>
amdgcn amd amdhsa opencl
amdgcn amd amdhsa amdgizcl
amdgcn amd amdhsa amdgiz
amdgcn amd amdhsa hcc
============ ======== ========= ===========
``r600-amd--``
Supports AMD GPUs HD2XXX-HD6XXX for graphics and compute shaders executed on
the MESA runtime.
``amdgcn-amd--``
Supports AMD GPUs GCN GFX6 onwards for graphics and compute shaders executed on
the MESA runtime.
``amdgcn-amd-amdhsa-``
Supports AMD GCN GPUs GFX6 onwards for compute kernels executed on HSA [HSA]_
compatible runtimes such as AMD's ROCm [AMD-ROCm]_.
``amdgcn-amd-amdhsa-opencl``
Supports AMD GCN GPUs GFX6 onwards for OpenCL compute kernels executed on HSA
[HSA]_ compatible runtimes such as AMD's ROCm [AMD-ROCm]_. See
:ref:`amdgpu-opencl`.
``amdgcn-amd-amdhsa-amdgizcl``
Same as ``amdgcn-amd-amdhsa-opencl`` except a different address space mapping
is used (see :ref:`amdgpu-address-spaces`).
``amdgcn-amd-amdhsa-amdgiz``
Same as ``amdgcn-amd-amdhsa-`` except a different address space mapping is
used (see :ref:`amdgpu-address-spaces`).
``amdgcn-amd-amdhsa-hcc``
Supports AMD GCN GPUs GFX6 onwards for AMD HC language compute kernels
executed on HSA [HSA]_ compatible runtimes such as AMD's ROCm [AMD-ROCm]_. See
:ref:`amdgpu-hcc`.
.. _amdgpu-processors:
Processors
----------
Use the ``clang -mcpu <Processor>`` option to specify the AMD GPU processor. The
names from both the *Processor* and *Alternative Processor* can be used.
.. table:: AMDGPU Processors
:name: amdgpu-processors-table
========== =========== ============ ===== ======= ==================
Processor Alternative Target dGPU/ Runtime Example
Processor Triple APU Support Products
Architecture
========== =========== ============ ===== ======= ==================
**Radeon HD 2000/3000 Series (R600)** [AMD-RADEON-HD-2000-3000]_
--------------------------------------------------------------------
r600 r600 dGPU
r630 r600 dGPU
rs880 r600 dGPU
rv670 r600 dGPU
**Radeon HD 4000 Series (R700)** [AMD-RADEON-HD-4000]_
--------------------------------------------------------------------
rv710 r600 dGPU
rv730 r600 dGPU
rv770 r600 dGPU
**Radeon HD 5000 Series (Evergreen)** [AMD-RADEON-HD-5000]_
--------------------------------------------------------------------
cedar r600 dGPU
redwood r600 dGPU
sumo r600 dGPU
juniper r600 dGPU
cypress r600 dGPU
**Radeon HD 6000 Series (Northern Islands)** [AMD-RADEON-HD-6000]_
--------------------------------------------------------------------
barts r600 dGPU
turks r600 dGPU
caicos r600 dGPU
cayman r600 dGPU
**GCN GFX6 (Southern Islands (SI))** [AMD-GCN-GFX6]_
--------------------------------------------------------------------
gfx600 - tahiti amdgcn dGPU
gfx601 - pitcairn amdgcn dGPU
- verde
- oland
- hainan
**GCN GFX7 (Sea Islands (CI))** [AMD-GCN-GFX7]_
--------------------------------------------------------------------
gfx700 - bonaire amdgcn dGPU - Radeon HD 7790
- Radeon HD 8770
- R7 260
- R7 260X
\ - kaveri amdgcn APU - A6-7000
- A6 Pro-7050B
- A8-7100
- A8 Pro-7150B
- A10-7300
- A10 Pro-7350B
- FX-7500
- A8-7200P
- A10-7400P
- FX-7600P
gfx701 - hawaii amdgcn dGPU ROCm - FirePro W8100
- FirePro W9100
- FirePro S9150
- FirePro S9170
gfx702 dGPU ROCm - Radeon R9 290
- Radeon R9 290x
- Radeon R390
- Radeon R390x
gfx703 - kabini amdgcn APU - E1-2100
- mullins - E1-2200
- E1-2500
- E2-3000
- E2-3800
- A4-5000
- A4-5100
- A6-5200
- A4 Pro-3340B
**GCN GFX8 (Volcanic Islands (VI))** [AMD-GCN-GFX8]_
--------------------------------------------------------------------
gfx800 - iceland amdgcn dGPU - FirePro S7150
- FirePro S7100
- FirePro W7100
- Radeon R285
- Radeon R9 380
- Radeon R9 385
- Mobile FirePro
M7170
gfx801 - carrizo amdgcn APU - A6-8500P
- Pro A6-8500B
- A8-8600P
- Pro A8-8600B
- FX-8800P
- Pro A12-8800B
\ amdgcn APU ROCm - A10-8700P
- Pro A10-8700B
- A10-8780P
\ amdgcn APU - A10-9600P
- A10-9630P
- A12-9700P
- A12-9730P
- FX-9800P
- FX-9830P
\ amdgcn APU - E2-9010
- A6-9210
- A9-9410
gfx802 - tonga amdgcn dGPU ROCm Same as gfx800
gfx803 - fiji amdgcn dGPU ROCm - Radeon R9 Nano
- Radeon R9 Fury
- Radeon R9 FuryX
- Radeon Pro Duo
- FirePro S9300x2
- Radeon Instinct MI8
\ - polaris10 amdgcn dGPU ROCm - Radeon RX 470
- Radeon RX 480
- Radeon Instinct MI6
\ - polaris11 amdgcn dGPU ROCm - Radeon RX 460
gfx804 amdgcn dGPU Same as gfx803
gfx810 - stoney amdgcn APU
**GCN GFX9** [AMD-GCN-GFX9]_
--------------------------------------------------------------------
gfx900 amdgcn dGPU - Radeon Vega
Frontier Edition
- Radeon RX Vega 56
- Radeon RX Vega 64
- Radeon RX Vega 64
Liquid
- Radeon Instinct MI25
gfx901 amdgcn dGPU ROCm Same as gfx900
except XNACK is
enabled
gfx902 amdgcn APU *TBA*
.. TODO
Add product
names.
gfx903 amdgcn APU Same as gfx902
except XNACK is
enabled
========== =========== ============ ===== ======= ==================
.. _amdgpu-address-spaces:
Address Spaces
--------------
The AMDGPU backend uses the following address space mappings.
The memory space names used in the table, aside from the region memory space, is
from the OpenCL standard.
LLVM Address Space number is used throughout LLVM (for example, in LLVM IR).
.. table:: Address Space Mapping
:name: amdgpu-address-space-mapping-table
================== ================= ================= ================= =================
LLVM Address Space Memory Space
------------------ -----------------------------------------------------------------------
\ Current Default amdgiz/amdgizcl hcc Future Default
================== ================= ================= ================= =================
0 Private (Scratch) Generic (Flat) Generic (Flat) Generic (Flat)
1 Global Global Global Global
2 Constant Constant Constant Region (GDS)
3 Local (group/LDS) Local (group/LDS) Local (group/LDS) Local (group/LDS)
4 Generic (Flat) Region (GDS) Region (GDS) Constant
5 Region (GDS) Private (Scratch) Private (Scratch) Private (Scratch)
================== ================= ================= ================= =================
Current Default
This is the current default address space mapping used for all languages
except hcc. This will shortly be deprecated.
amdgiz/amdgizcl
This is the current address space mapping used when ``amdgiz`` or ``amdgizcl``
is specified as the target triple environment value.
hcc
This is the current address space mapping used when ``hcc`` is specified as
the target triple environment value.This will shortly be deprecated.
Future Default
This will shortly be the only address space mapping for all languages using
AMDGPU backend.
.. _amdgpu-memory-scopes:
Memory Scopes
-------------
This section provides LLVM memory synchronization scopes supported by the AMDGPU
backend memory model when the target triple OS is ``amdhsa`` (see
:ref:`amdgpu-amdhsa-memory-model` and :ref:`amdgpu-target-triples`).
The memory model supported is based on the HSA memory model [HSA]_ which is
based in turn on HRF-indirect with scope inclusion [HRF]_. The happens-before
relation is transitive over the synchonizes-with relation independent of scope,
and synchonizes-with allows the memory scope instances to be inclusive (see
table :ref:`amdgpu-amdhsa-llvm-sync-scopes-amdhsa-table`).
This is different to the OpenCL [OpenCL]_ memory model which does not have scope
inclusion and requires the memory scopes to exactly match. However, this
is conservatively correct for OpenCL.
.. table:: AMDHSA LLVM Sync Scopes for AMDHSA
:name: amdgpu-amdhsa-llvm-sync-scopes-amdhsa-table
================ ==========================================================
LLVM Sync Scope Description
================ ==========================================================
*none* The default: ``system``.
Synchronizes with, and participates in modification and
seq_cst total orderings with, other operations (except
image operations) for all address spaces (except private,
or generic that accesses private) provided the other
operation's sync scope is:
- ``system``.
- ``agent`` and executed by a thread on the same agent.
- ``workgroup`` and executed by a thread in the same
workgroup.
- ``wavefront`` and executed by a thread in the same
wavefront.
``agent`` Synchronizes with, and participates in modification and
seq_cst total orderings with, other operations (except
image operations) for all address spaces (except private,
or generic that accesses private) provided the other
operation's sync scope is:
- ``system`` or ``agent`` and executed by a thread on the
same agent.
- ``workgroup`` and executed by a thread in the same
workgroup.
- ``wavefront`` and executed by a thread in the same
wavefront.
``workgroup`` Synchronizes with, and participates in modification and
seq_cst total orderings with, other operations (except
image operations) for all address spaces (except private,
or generic that accesses private) provided the other
operation's sync scope is:
- ``system``, ``agent`` or ``workgroup`` and executed by a
thread in the same workgroup.
- ``wavefront`` and executed by a thread in the same
wavefront.
``wavefront`` Synchronizes with, and participates in modification and
seq_cst total orderings with, other operations (except
image operations) for all address spaces (except private,
or generic that accesses private) provided the other
operation's sync scope is:
- ``system``, ``agent``, ``workgroup`` or ``wavefront``
and executed by a thread in the same wavefront.
``singlethread`` Only synchronizes with, and participates in modification
and seq_cst total orderings with, other operations (except
image operations) running in the same thread for all
address spaces (for example, in signal handlers).
================ ==========================================================
AMDGPU Intrinsics
-----------------
The AMDGPU backend implements the following intrinsics.
*This section is WIP.*
.. TODO
List AMDGPU intrinsics
Code Object
===========
The AMDGPU backend generates a standard ELF [ELF]_ relocatable code object that
can be linked by ``lld`` to produce a standard ELF shared code object which can
be loaded and executed on an AMDGPU target.
Header
------
The AMDGPU backend uses the following ELF header:
.. table:: AMDGPU ELF Header
:name: amdgpu-elf-header-table
========================== ===============================
Field Value
========================== ===============================
``e_ident[EI_CLASS]`` ``ELFCLASS64``
``e_ident[EI_DATA]`` ``ELFDATA2LSB``
``e_ident[EI_OSABI]`` ``ELFOSABI_AMDGPU_HSA``,
``ELFOSABI_AMDGPU_PAL`` or
``ELFOSABI_AMDGPU_MESA3D``
``e_ident[EI_ABIVERSION]`` ``ELFABIVERSION_AMDGPU_HSA``,
``ELFABIVERSION_AMDGPU_PAL`` or
``ELFABIVERSION_AMDGPU_MESA3D``
``e_type`` ``ET_REL`` or ``ET_DYN``
``e_machine`` ``EM_AMDGPU``
``e_entry`` 0
``e_flags`` 0
========================== ===============================
..
.. table:: AMDGPU ELF Header Enumeration Values
:name: amdgpu-elf-header-enumeration-values-table
=============================== =====
Name Value
=============================== =====
``EM_AMDGPU`` 224
``ELFOSABI_AMDGPU_HSA`` 64
``ELFOSABI_AMDGPU_PAL`` 65
``ELFOSABI_AMDGPU_MESA3D`` 66
``ELFABIVERSION_AMDGPU_HSA`` 1
``ELFABIVERSION_AMDGPU_PAL`` 0
``ELFABIVERSION_AMDGPU_MESA3D`` 0
=============================== =====
``e_ident[EI_CLASS]``
The ELF class is always ``ELFCLASS64``. The AMDGPU backend only supports 64
bit applications.
``e_ident[EI_DATA]``
All AMDGPU targets use ELFDATA2LSB for little-endian byte ordering.
``e_ident[EI_OSABI]``
One of the following AMD GPU architecture specific OS ABIs:
* ``ELFOSABI_AMDGPU_HSA`` is used to specify that the code object conforms to
the AMD HSA runtime ABI [HSA]_.
* ``ELFOSABI_AMDGPU_PAL`` is used to specify that the code object conforms to
the AMD PAL runtime ABI.
* ``ELFOSABI_AMDGPU_MESA3D`` is used to specify that the code object conforms
to the AMD MESA runtime ABI.
``e_ident[EI_ABIVERSION]``
The ABI version of the AMD GPU architecture specific OS ABI to which the code
object conforms:
* ``ELFABIVERSION_AMDGPU_HSA`` is used to specify the version of AMD HSA
runtime ABI.
* ``ELFABIVERSION_AMDGPU_PAL`` is used to specify the version of AMD PAL
runtime ABI.
* ``ELFABIVERSION_AMDGPU_MESA3D`` is used to specify the version of AMD MESA
runtime ABI.
``e_type``
Can be one of the following values:
``ET_REL``
The type produced by the AMD GPU backend compiler as it is relocatable code
object.
``ET_DYN``
The type produced by the linker as it is a shared code object.
The AMD HSA runtime loader requires a ``ET_DYN`` code object.
``e_machine``
The value ``EM_AMDGPU`` is used for the machine for all members of the AMD GPU
architecture family. The specific member is specified in the
``NT_AMD_AMDGPU_ISA`` entry in the ``.note`` section (see
:ref:`amdgpu-note-records`).
``e_entry``
The entry point is 0 as the entry points for individual kernels must be
selected in order to invoke them through AQL packets.
``e_flags``
The value is 0 as no flags are used.
Sections
--------
An AMDGPU target ELF code object has the standard ELF sections which include:
.. table:: AMDGPU ELF Sections
:name: amdgpu-elf-sections-table
================== ================ =================================
Name Type Attributes
================== ================ =================================
``.bss`` ``SHT_NOBITS`` ``SHF_ALLOC`` + ``SHF_WRITE``
``.data`` ``SHT_PROGBITS`` ``SHF_ALLOC`` + ``SHF_WRITE``
``.debug_``\ *\** ``SHT_PROGBITS`` *none*
``.dynamic`` ``SHT_DYNAMIC`` ``SHF_ALLOC``
``.dynstr`` ``SHT_PROGBITS`` ``SHF_ALLOC``
``.dynsym`` ``SHT_PROGBITS`` ``SHF_ALLOC``
``.got`` ``SHT_PROGBITS`` ``SHF_ALLOC`` + ``SHF_WRITE``
``.hash`` ``SHT_HASH`` ``SHF_ALLOC``
``.note`` ``SHT_NOTE`` *none*
``.rela``\ *name* ``SHT_RELA`` *none*
``.rela.dyn`` ``SHT_RELA`` *none*
``.rodata`` ``SHT_PROGBITS`` ``SHF_ALLOC``
``.shstrtab`` ``SHT_STRTAB`` *none*
``.strtab`` ``SHT_STRTAB`` *none*
``.symtab`` ``SHT_SYMTAB`` *none*
``.text`` ``SHT_PROGBITS`` ``SHF_ALLOC`` + ``SHF_EXECINSTR``
================== ================ =================================
These sections have their standard meanings (see [ELF]_) and are only generated
if needed.
``.debug``\ *\**
The standard DWARF sections. See :ref:`amdgpu-dwarf` for information on the
DWARF produced by the AMDGPU backend.
``.dynamic``, ``.dynstr``, ``.dynsym``, ``.hash``
The standard sections used by a dynamic loader.
``.note``
See :ref:`amdgpu-note-records` for the note records supported by the AMDGPU
backend.
``.rela``\ *name*, ``.rela.dyn``
For relocatable code objects, *name* is the name of the section that the
relocation records apply. For example, ``.rela.text`` is the section name for
relocation records associated with the ``.text`` section.
For linked shared code objects, ``.rela.dyn`` contains all the relocation
records from each of the relocatable code object's ``.rela``\ *name* sections.
See :ref:`amdgpu-relocation-records` for the relocation records supported by
the AMDGPU backend.
``.text``
The executable machine code for the kernels and functions they call. Generated
as position independent code. See :ref:`amdgpu-code-conventions` for
information on conventions used in the isa generation.
.. _amdgpu-note-records:
Note Records
------------
As required by ``ELFCLASS64``, minimal zero byte padding must be generated after
the ``name`` field to ensure the ``desc`` field is 4 byte aligned. In addition,
minimal zero byte padding must be generated to ensure the ``desc`` field size is
a multiple of 4 bytes. The ``sh_addralign`` field of the ``.note`` section must
be at least 4 to indicate at least 8 byte alignment.
The AMDGPU backend code object uses the following ELF note records in the
``.note`` section. The *Description* column specifies the layout of the note
record's ``desc`` field. All fields are consecutive bytes. Note records with
variable size strings have a corresponding ``*_size`` field that specifies the
number of bytes, including the terminating null character, in the string. The
string(s) come immediately after the preceding fields.
Additional note records can be present.
.. table:: AMDGPU ELF Note Records
:name: amdgpu-elf-note-records-table
===== ============================== ======================================
Name Type Description
===== ============================== ======================================
"AMD" ``NT_AMD_AMDGPU_HSA_METADATA`` <metadata null terminated string>
"AMD" ``NT_AMD_AMDGPU_ISA`` <isa name null terminated string>
===== ============================== ======================================
..
.. table:: AMDGPU ELF Note Record Enumeration Values
:name: amdgpu-elf-note-record-enumeration-values-table
============================== =====
Name Value
============================== =====
*reserved* 0-9
``NT_AMD_AMDGPU_HSA_METADATA`` 10
``NT_AMD_AMDGPU_ISA`` 11
============================== =====
``NT_AMD_AMDGPU_ISA``
Specifies the instruction set architecture used by the machine code contained
in the code object.
This note record is required for code objects containing machine code for
processors matching the ``amdgcn`` architecture in table
:ref:`amdgpu-processors`.
The null terminated string has the following syntax:
*architecture*\ ``-``\ *vendor*\ ``-``\ *os*\ ``-``\ *environment*\ ``-``\ *processor*
where:
*architecture*
The architecture from table :ref:`amdgpu-target-triples-table`.
This is always ``amdgcn`` when the target triple OS is ``amdhsa`` (see
:ref:`amdgpu-target-triples`).
*vendor*
The vendor from table :ref:`amdgpu-target-triples-table`.
For the AMDGPU backend this is always ``amd``.
*os*
The OS from table :ref:`amdgpu-target-triples-table`.
*environment*
An environment from table :ref:`amdgpu-target-triples-table`, or blank if
the environment has no affect on the execution of the code object.
For the AMDGPU backend this is currently always blank.
*processor*
The processor from table :ref:`amdgpu-processors-table`.
For example:
``amdgcn-amd-amdhsa--gfx901``
``NT_AMD_AMDGPU_HSA_METADATA``
Specifies extensible metadata associated with the code objects executed on HSA
[HSA]_ compatible runtimes such as AMD's ROCm [AMD-ROCm]_. It is required when
the target triple OS is ``amdhsa`` (see :ref:`amdgpu-target-triples`). See
:ref:`amdgpu-amdhsa-hsa-code-object-metadata` for the syntax of the code
object metadata string.
.. _amdgpu-symbols:
Symbols
-------
Symbols include the following:
.. table:: AMDGPU ELF Symbols
:name: amdgpu-elf-symbols-table
===================== ============== ============= ==================
Name Type Section Description
===================== ============== ============= ==================
*link-name* ``STT_OBJECT`` - ``.data`` Global variable
- ``.rodata``
- ``.bss``
*link-name*\ ``@kd`` ``STT_OBJECT`` - ``.rodata`` Kernel descriptor
*link-name* ``STT_FUNC`` - ``.text`` Kernel entry point
===================== ============== ============= ==================
Global variable
Global variables both used and defined by the compilation unit.
If the symbol is defined in the compilation unit then it is allocated in the
appropriate section according to if it has initialized data or is readonly.
If the symbol is external then its section is ``STN_UNDEF`` and the loader
will resolve relocations using the definition provided by another code object
or explicitly defined by the runtime.
All global symbols, whether defined in the compilation unit or external, are
accessed by the machine code indirectly through a GOT table entry. This
allows them to be preemptable. The GOT table is only supported when the target
triple OS is ``amdhsa`` (see :ref:`amdgpu-target-triples`).
.. TODO
Add description of linked shared object symbols. Seems undefined symbols
are marked as STT_NOTYPE.
Kernel descriptor
Every HSA kernel has an associated kernel descriptor. It is the address of the
kernel descriptor that is used in the AQL dispatch packet used to invoke the
kernel, not the kernel entry point. The layout of the HSA kernel descriptor is
defined in :ref:`amdgpu-amdhsa-kernel-descriptor`.
Kernel entry point
Every HSA kernel also has a symbol for its machine code entry point.
.. _amdgpu-relocation-records:
Relocation Records
------------------
AMDGPU backend generates ``Elf64_Rela`` relocation records. Supported
relocatable fields are:
``word32``
This specifies a 32-bit field occupying 4 bytes with arbitrary byte
alignment. These values use the same byte order as other word values in the
AMD GPU architecture.
``word64``
This specifies a 64-bit field occupying 8 bytes with arbitrary byte
alignment. These values use the same byte order as other word values in the
AMD GPU architecture.
Following notations are used for specifying relocation calculations:
**A**
Represents the addend used to compute the value of the relocatable field.
**G**
Represents the offset into the global offset table at which the relocation
entry's symbol will reside during execution.
**GOT**
Represents the address of the global offset table.
**P**
Represents the place (section offset for ``et_rel`` or address for ``et_dyn``)
of the storage unit being relocated (computed using ``r_offset``).
**S**
Represents the value of the symbol whose index resides in the relocation
entry. Relocations not using this must specify a symbol index of ``STN_UNDEF``.
**B**
Represents the base address of a loaded executable or shared object which is
the difference between the ELF address and the actual load address. Relocations
using this are only valid in executable or shared objects.
The following relocation types are supported:
.. table:: AMDGPU ELF Relocation Records
:name: amdgpu-elf-relocation-records-table
========================== ===== ========== ==============================
Relocation Type Value Field Calculation
========================== ===== ========== ==============================
``R_AMDGPU_NONE`` 0 *none* *none*
``R_AMDGPU_ABS32_LO`` 1 ``word32`` (S + A) & 0xFFFFFFFF
``R_AMDGPU_ABS32_HI`` 2 ``word32`` (S + A) >> 32
``R_AMDGPU_ABS64`` 3 ``word64`` S + A
``R_AMDGPU_REL32`` 4 ``word32`` S + A - P
``R_AMDGPU_REL64`` 5 ``word64`` S + A - P
``R_AMDGPU_ABS32`` 6 ``word32`` S + A
``R_AMDGPU_GOTPCREL`` 7 ``word32`` G + GOT + A - P
``R_AMDGPU_GOTPCREL32_LO`` 8 ``word32`` (G + GOT + A - P) & 0xFFFFFFFF
``R_AMDGPU_GOTPCREL32_HI`` 9 ``word32`` (G + GOT + A - P) >> 32
``R_AMDGPU_REL32_LO`` 10 ``word32`` (S + A - P) & 0xFFFFFFFF
``R_AMDGPU_REL32_HI`` 11 ``word32`` (S + A - P) >> 32
*reserved* 12
``R_AMDGPU_RELATIVE64`` 13 ``word64`` B + A
========================== ===== ========== ==============================
.. _amdgpu-dwarf:
DWARF
-----
Standard DWARF [DWARF]_ Version 2 sections can be generated. These contain
information that maps the code object executable code and data to the source
language constructs. It can be used by tools such as debuggers and profilers.
Address Space Mapping
~~~~~~~~~~~~~~~~~~~~~
The following address space mapping is used:
.. table:: AMDGPU DWARF Address Space Mapping
:name: amdgpu-dwarf-address-space-mapping-table
=================== =================
DWARF Address Space Memory Space
=================== =================
1 Private (Scratch)
2 Local (group/LDS)
*omitted* Global
*omitted* Constant
*omitted* Generic (Flat)
*not supported* Region (GDS)
=================== =================
See :ref:`amdgpu-address-spaces` for information on the memory space terminology
used in the table.
An ``address_class`` attribute is generated on pointer type DIEs to specify the
DWARF address space of the value of the pointer when it is in the *private* or
*local* address space. Otherwise the attribute is omitted.
An ``XDEREF`` operation is generated in location list expressions for variables
that are allocated in the *private* and *local* address space. Otherwise no
``XDREF`` is omitted.
Register Mapping
~~~~~~~~~~~~~~~~
*This section is WIP.*
.. TODO
Define DWARF register enumeration.
If want to present a wavefront state then should expose vector registers as
64 wide (rather than per work-item view that LLVM uses). Either as separate
registers, or a 64x4 byte single register. In either case use a new LANE op
(akin to XDREF) to select the current lane usage in a location
expression. This would also allow scalar register spilling to vector register
lanes to be expressed (currently no debug information is being generated for
spilling). If choose a wide single register approach then use LANE in
conjunction with PIECE operation to select the dword part of the register for
the current lane. If the separate register approach then use LANE to select
the register.
Source Text
~~~~~~~~~~~
*This section is WIP.*
.. TODO
DWARF extension to include runtime generated source text.
.. _amdgpu-code-conventions:
Code Conventions
================
This section provides code conventions used for each supported target triple OS
(see :ref:`amdgpu-target-triples`).
AMDHSA
------
This section provides code conventions used when the target triple OS is
``amdhsa`` (see :ref:`amdgpu-target-triples`).
.. _amdgpu-amdhsa-hsa-code-object-metadata:
Code Object Metadata
~~~~~~~~~~~~~~~~~~~~
The code object metadata specifies extensible metadata associated with the code
objects executed on HSA [HSA]_ compatible runtimes such as AMD's ROCm
[AMD-ROCm]_. It is specified by the ``NT_AMD_AMDGPU_HSA_METADATA`` note record
(see :ref:`amdgpu-note-records`) and is required when the target triple OS is
``amdhsa`` (see :ref:`amdgpu-target-triples`). It must contain the minimum
information necessary to support the ROCM kernel queries. For example, the
segment sizes needed in a dispatch packet. In addition, a high level language
runtime may require other information to be included. For example, the AMD
OpenCL runtime records kernel argument information.
The metadata is specified as a YAML formatted string (see [YAML]_ and
:doc:`YamlIO`).
.. TODO
Is the string null terminated? It probably should not if YAML allows it to
contain null characters, otherwise it should be.
The metadata is represented as a single YAML document comprised of the mapping
defined in table :ref:`amdgpu-amdhsa-code-object-metadata-mapping-table` and
referenced tables.
For boolean values, the string values of ``false`` and ``true`` are used for
false and true respectively.
Additional information can be added to the mappings. To avoid conflicts, any
non-AMD key names should be prefixed by "*vendor-name*.".
.. table:: AMDHSA Code Object Metadata Mapping
:name: amdgpu-amdhsa-code-object-metadata-mapping-table
========== ============== ========= =======================================
String Key Value Type Required? Description
========== ============== ========= =======================================
"Version" sequence of Required - The first integer is the major
2 integers version. Currently 1.
- The second integer is the minor
version. Currently 0.
"Printf" sequence of Each string is encoded information
strings about a printf function call. The
encoded information is organized as
fields separated by colon (':'):
``ID:N:S[0]:S[1]:...:S[N-1]:FormatString``
where:
``ID``
A 32 bit integer as a unique id for
each printf function call
``N``
A 32 bit integer equal to the number
of arguments of printf function call
minus 1
``S[i]`` (where i = 0, 1, ... , N-1)
32 bit integers for the size in bytes
of the i-th FormatString argument of
the printf function call
FormatString
The format string passed to the
printf function call.
"Kernels" sequence of Required Sequence of the mappings for each
mapping kernel in the code object. See
:ref:`amdgpu-amdhsa-code-object-kernel-metadata-mapping-table`
for the definition of the mapping.
========== ============== ========= =======================================
..
.. table:: AMDHSA Code Object Kernel Metadata Mapping
:name: amdgpu-amdhsa-code-object-kernel-metadata-mapping-table
================= ============== ========= ================================
String Key Value Type Required? Description
================= ============== ========= ================================
"Name" string Required Source name of the kernel.
"SymbolName" string Required Name of the kernel
descriptor ELF symbol.
"Language" string Source language of the kernel.
Values include:
- "OpenCL C"
- "OpenCL C++"
- "HCC"
- "OpenMP"
"LanguageVersion" sequence of - The first integer is the major
2 integers version.
- The second integer is the
minor version.
"Attrs" mapping Mapping of kernel attributes.
See
:ref:`amdgpu-amdhsa-code-object-kernel-attribute-metadata-mapping-table`
for the mapping definition.
"Args" sequence of Sequence of mappings of the
mapping kernel arguments. See
:ref:`amdgpu-amdhsa-code-object-kernel-argument-metadata-mapping-table`
for the definition of the mapping.
"CodeProps" mapping Mapping of properties related to
the kernel code. See
:ref:`amdgpu-amdhsa-code-object-kernel-code-properties-metadata-mapping-table`
for the mapping definition.
"DebugProps" mapping Mapping of properties related to
the kernel debugging. See
:ref:`amdgpu-amdhsa-code-object-kernel-debug-properties-metadata-mapping-table`
for the mapping definition.
================= ============== ========= ================================
..
.. table:: AMDHSA Code Object Kernel Attribute Metadata Mapping
:name: amdgpu-amdhsa-code-object-kernel-attribute-metadata-mapping-table
=================== ============== ========= ==============================
String Key Value Type Required? Description
=================== ============== ========= ==============================
"ReqdWorkGroupSize" sequence of The dispatch work-group size
3 integers X, Y, Z must correspond to the
specified values.
Corresponds to the OpenCL
``reqd_work_group_size``
attribute.
"WorkGroupSizeHint" sequence of The dispatch work-group size
3 integers X, Y, Z is likely to be the
specified values.
Corresponds to the OpenCL
``work_group_size_hint``
attribute.
"VecTypeHint" string The name of a scalar or vector
type.
Corresponds to the OpenCL
``vec_type_hint`` attribute.
"RuntimeHandle" string The external symbol name
associated with a kernel.
OpenCL runtime allocates a
global buffer for the symbol
and saves the kernel's address
to it, which is used for
device side enqueueing. Only
available for device side
enqueued kernels.
=================== ============== ========= ==============================
..
.. table:: AMDHSA Code Object Kernel Argument Metadata Mapping
:name: amdgpu-amdhsa-code-object-kernel-argument-metadata-mapping-table
================= ============== ========= ================================
String Key Value Type Required? Description
================= ============== ========= ================================
"Name" string Kernel argument name.
"TypeName" string Kernel argument type name.
"Size" integer Required Kernel argument size in bytes.
"Align" integer Required Kernel argument alignment in
bytes. Must be a power of two.
"ValueKind" string Required Kernel argument kind that
specifies how to set up the
corresponding argument.
Values include:
"ByValue"
The argument is copied
directly into the kernarg.
"GlobalBuffer"
A global address space pointer
to the buffer data is passed
in the kernarg.
"DynamicSharedPointer"
A group address space pointer
to dynamically allocated LDS
is passed in the kernarg.
"Sampler"
A global address space
pointer to a S# is passed in
the kernarg.
"Image"
A global address space
pointer to a T# is passed in
the kernarg.
"Pipe"
A global address space pointer
to an OpenCL pipe is passed in
the kernarg.
"Queue"
A global address space pointer
to an OpenCL device enqueue
queue is passed in the
kernarg.
"HiddenGlobalOffsetX"
The OpenCL grid dispatch
global offset for the X
dimension is passed in the
kernarg.
"HiddenGlobalOffsetY"
The OpenCL grid dispatch
global offset for the Y
dimension is passed in the
kernarg.
"HiddenGlobalOffsetZ"
The OpenCL grid dispatch
global offset for the Z
dimension is passed in the
kernarg.
"HiddenNone"
An argument that is not used
by the kernel. Space needs to
be left for it, but it does
not need to be set up.
"HiddenPrintfBuffer"
A global address space pointer
to the runtime printf buffer
is passed in kernarg.
"HiddenDefaultQueue"
A global address space pointer
to the OpenCL device enqueue
queue that should be used by
the kernel by default is
passed in the kernarg.
"HiddenCompletionAction"
*TBD*
.. TODO
Add description.
"ValueType" string Required Kernel argument value type. Only
present if "ValueKind" is
"ByValue". For vector data
types, the value is for the
element type. Values include:
- "Struct"
- "I8"
- "U8"
- "I16"
- "U16"
- "F16"
- "I32"
- "U32"
- "F32"
- "I64"
- "U64"
- "F64"
.. TODO
How can it be determined if a
vector type, and what size
vector?
"PointeeAlign" integer Alignment in bytes of pointee
type for pointer type kernel
argument. Must be a power
of 2. Only present if
"ValueKind" is
"DynamicSharedPointer".
"AddrSpaceQual" string Kernel argument address space
qualifier. Only present if
"ValueKind" is "GlobalBuffer" or
"DynamicSharedPointer". Values
are:
- "Private"
- "Global"
- "Constant"
- "Local"
- "Generic"
- "Region"
.. TODO
Is GlobalBuffer only Global
or Constant? Is
DynamicSharedPointer always
Local? Can HCC allow Generic?
How can Private or Region
ever happen?
"AccQual" string Kernel argument access
qualifier. Only present if
"ValueKind" is "Image" or
"Pipe". Values
are:
- "ReadOnly"
- "WriteOnly"
- "ReadWrite"
.. TODO
Does this apply to
GlobalBuffer?
"ActualAccQual" string The actual memory accesses
performed by the kernel on the
kernel argument. Only present if
"ValueKind" is "GlobalBuffer",
"Image", or "Pipe". This may be
more restrictive than indicated
by "AccQual" to reflect what the
kernel actual does. If not
present then the runtime must
assume what is implied by
"AccQual" and "IsConst". Values
are:
- "ReadOnly"
- "WriteOnly"
- "ReadWrite"
"IsConst" boolean Indicates if the kernel argument
is const qualified. Only present
if "ValueKind" is
"GlobalBuffer".
"IsRestrict" boolean Indicates if the kernel argument
is restrict qualified. Only
present if "ValueKind" is
"GlobalBuffer".
"IsVolatile" boolean Indicates if the kernel argument
is volatile qualified. Only
present if "ValueKind" is
"GlobalBuffer".
"IsPipe" boolean Indicates if the kernel argument
is pipe qualified. Only present
if "ValueKind" is "Pipe".
.. TODO
Can GlobalBuffer be pipe
qualified?
================= ============== ========= ================================
..
.. table:: AMDHSA Code Object Kernel Code Properties Metadata Mapping
:name: amdgpu-amdhsa-code-object-kernel-code-properties-metadata-mapping-table
============================ ============== ========= =====================
String Key Value Type Required? Description
============================ ============== ========= =====================
"KernargSegmentSize" integer Required The size in bytes of
the kernarg segment
that holds the values
of the arguments to
the kernel.
"GroupSegmentFixedSize" integer Required The amount of group
segment memory
required by a
work-group in
bytes. This does not
include any
dynamically allocated
group segment memory
that may be added
when the kernel is
dispatched.
"PrivateSegmentFixedSize" integer Required The amount of fixed
private address space
memory required for a
work-item in
bytes. If
IsDynamicCallstack
is 1 then additional
space must be added
to this value for the
call stack.
"KernargSegmentAlign" integer Required The maximum byte
alignment of
arguments in the
kernarg segment. Must
be a power of 2.
"WavefrontSize" integer Required Wavefront size. Must
be a power of 2.
"NumSGPRs" integer Number of scalar
registers used by a
wavefront for
GFX6-GFX9. This
includes the special
SGPRs for VCC, Flat
Scratch (GFX7-GFX9)
and XNACK (for
GFX8-GFX9). It does
not include the 16
SGPR added if a trap
handler is
enabled. It is not
rounded up to the
allocation
granularity.
"NumVGPRs" integer Number of vector
registers used by
each work-item for
GFX6-GFX9
"MaxFlatWorkGroupSize" integer Maximum flat
work-group size
supported by the
kernel in work-items.
"IsDynamicCallStack" boolean Indicates if the
generated machine
code is using a
dynamically sized
call stack.
"IsXNACKEnabled" boolean Indicates if the
generated machine
code is capable of
supporting XNACK.
============================ ============== ========= =====================
..
.. table:: AMDHSA Code Object Kernel Debug Properties Metadata Mapping
:name: amdgpu-amdhsa-code-object-kernel-debug-properties-metadata-mapping-table
=================================== ============== ========= ==============
String Key Value Type Required? Description
=================================== ============== ========= ==============
"DebuggerABIVersion" sequence of
2 integers
"ReservedNumVGPRs" integer
"ReservedFirstVGPR" integer
"PrivateSegmentBufferSGPR" integer
"WavefrontPrivateSegmentOffsetSGPR" integer
=================================== ============== ========= ==============
.. TODO
Plan to remove the debug properties metadata.
Kernel Dispatch
~~~~~~~~~~~~~~~
The HSA architected queuing language (AQL) defines a user space memory interface
that can be used to control the dispatch of kernels, in an agent independent
way. An agent can have zero or more AQL queues created for it using the ROCm
runtime, in which AQL packets (all of which are 64 bytes) can be placed. See the
*HSA Platform System Architecture Specification* [HSA]_ for the AQL queue
mechanics and packet layouts.
The packet processor of a kernel agent is responsible for detecting and
dispatching HSA kernels from the AQL queues associated with it. For AMD GPUs the
packet processor is implemented by the hardware command processor (CP),
asynchronous dispatch controller (ADC) and shader processor input controller
(SPI).
The ROCm runtime can be used to allocate an AQL queue object. It uses the kernel
mode driver to initialize and register the AQL queue with CP.
To dispatch a kernel the following actions are performed. This can occur in the
CPU host program, or from an HSA kernel executing on a GPU.
1. A pointer to an AQL queue for the kernel agent on which the kernel is to be
executed is obtained.
2. A pointer to the kernel descriptor (see
:ref:`amdgpu-amdhsa-kernel-descriptor`) of the kernel to execute is
obtained. It must be for a kernel that is contained in a code object that that
was loaded by the ROCm runtime on the kernel agent with which the AQL queue is
associated.
3. Space is allocated for the kernel arguments using the ROCm runtime allocator
for a memory region with the kernarg property for the kernel agent that will
execute the kernel. It must be at least 16 byte aligned.
4. Kernel argument values are assigned to the kernel argument memory
allocation. The layout is defined in the *HSA Programmer's Language Reference*
[HSA]_. For AMDGPU the kernel execution directly accesses the kernel argument
memory in the same way constant memory is accessed. (Note that the HSA
specification allows an implementation to copy the kernel argument contents to
another location that is accessed by the kernel.)
5. An AQL kernel dispatch packet is created on the AQL queue. The ROCm runtime
api uses 64 bit atomic operations to reserve space in the AQL queue for the
packet. The packet must be set up, and the final write must use an atomic
store release to set the packet kind to ensure the packet contents are
visible to the kernel agent. AQL defines a doorbell signal mechanism to
notify the kernel agent that the AQL queue has been updated. These rules, and
the layout of the AQL queue and kernel dispatch packet is defined in the *HSA
System Architecture Specification* [HSA]_.
6. A kernel dispatch packet includes information about the actual dispatch,
such as grid and work-group size, together with information from the code
object about the kernel, such as segment sizes. The ROCm runtime queries on
the kernel symbol can be used to obtain the code object values which are
recorded in the :ref:`amdgpu-amdhsa-hsa-code-object-metadata`.
7. CP executes micro-code and is responsible for detecting and setting up the
GPU to execute the wavefronts of a kernel dispatch.
8. CP ensures that when the a wavefront starts executing the kernel machine
code, the scalar general purpose registers (SGPR) and vector general purpose
registers (VGPR) are set up as required by the machine code. The required
setup is defined in the :ref:`amdgpu-amdhsa-kernel-descriptor`. The initial
register state is defined in
:ref:`amdgpu-amdhsa-initial-kernel-execution-state`.
9. The prolog of the kernel machine code (see
:ref:`amdgpu-amdhsa-kernel-prolog`) sets up the machine state as necessary
before continuing executing the machine code that corresponds to the kernel.
10. When the kernel dispatch has completed execution, CP signals the completion
signal specified in the kernel dispatch packet if not 0.
.. _amdgpu-amdhsa-memory-spaces:
Memory Spaces
~~~~~~~~~~~~~
The memory space properties are:
.. table:: AMDHSA Memory Spaces
:name: amdgpu-amdhsa-memory-spaces-table
================= =========== ======== ======= ==================
Memory Space Name HSA Segment Hardware Address NULL Value
Name Name Size
================= =========== ======== ======= ==================
Private private scratch 32 0x00000000
Local group LDS 32 0xFFFFFFFF
Global global global 64 0x0000000000000000
Constant constant *same as 64 0x0000000000000000
global*
Generic flat flat 64 0x0000000000000000
Region N/A GDS 32 *not implemented
for AMDHSA*
================= =========== ======== ======= ==================
The global and constant memory spaces both use global virtual addresses, which
are the same virtual address space used by the CPU. However, some virtual
addresses may only be accessible to the CPU, some only accessible by the GPU,
and some by both.
Using the constant memory space indicates that the data will not change during
the execution of the kernel. This allows scalar read instructions to be
used. The vector and scalar L1 caches are invalidated of volatile data before
each kernel dispatch execution to allow constant memory to change values between
kernel dispatches.
The local memory space uses the hardware Local Data Store (LDS) which is
automatically allocated when the hardware creates work-groups of wavefronts, and
freed when all the wavefronts of a work-group have terminated. The data store
(DS) instructions can be used to access it.
The private memory space uses the hardware scratch memory support. If the kernel
uses scratch, then the hardware allocates memory that is accessed using
wavefront lane dword (4 byte) interleaving. The mapping used from private
address to physical address is:
``wavefront-scratch-base +
(private-address * wavefront-size * 4) +
(wavefront-lane-id * 4)``
There are different ways that the wavefront scratch base address is determined
by a wavefront (see :ref:`amdgpu-amdhsa-initial-kernel-execution-state`). This
memory can be accessed in an interleaved manner using buffer instruction with
the scratch buffer descriptor and per wave scratch offset, by the scratch
instructions, or by flat instructions. If each lane of a wavefront accesses the
same private address, the interleaving results in adjacent dwords being accessed
and hence requires fewer cache lines to be fetched. Multi-dword access is not
supported except by flat and scratch instructions in GFX9.
The generic address space uses the hardware flat address support available in
GFX7-GFX9. This uses two fixed ranges of virtual addresses (the private and
local appertures), that are outside the range of addressible global memory, to
map from a flat address to a private or local address.
FLAT instructions can take a flat address and access global, private (scratch)
and group (LDS) memory depending in if the address is within one of the
apperture ranges. Flat access to scratch requires hardware aperture setup and
setup in the kernel prologue (see :ref:`amdgpu-amdhsa-flat-scratch`). Flat
access to LDS requires hardware aperture setup and M0 (GFX7-GFX8) register setup
(see :ref:`amdgpu-amdhsa-m0`).
To convert between a segment address and a flat address the base address of the
appertures address can be used. For GFX7-GFX8 these are available in the
:ref:`amdgpu-amdhsa-hsa-aql-queue` the address of which can be obtained with
Queue Ptr SGPR (see :ref:`amdgpu-amdhsa-initial-kernel-execution-state`). For
GFX9 the appature base addresses are directly available as inline constant
registers ``SRC_SHARED_BASE/LIMIT`` and ``SRC_PRIVATE_BASE/LIMIT``. In 64 bit
address mode the apperture sizes are 2^32 bytes and the base is aligned to 2^32
which makes it easier to convert from flat to segment or segment to flat.
Image and Samplers
~~~~~~~~~~~~~~~~~~
Image and sample handles created by the ROCm runtime are 64 bit addresses of a
hardware 32 byte V# and 48 byte S# object respectively. In order to support the
HSA ``query_sampler`` operations two extra dwords are used to store the HSA BRIG
enumeration values for the queries that are not trivially deducible from the S#
representation.
HSA Signals
~~~~~~~~~~~
HSA signal handles created by the ROCm runtime are 64 bit addresses of a
structure allocated in memory accessible from both the CPU and GPU. The
structure is defined by the ROCm runtime and subject to change between releases
(see [AMD-ROCm-github]_).
.. _amdgpu-amdhsa-hsa-aql-queue:
HSA AQL Queue
~~~~~~~~~~~~~
The HSA AQL queue structure is defined by the ROCm runtime and subject to change
between releases (see [AMD-ROCm-github]_). For some processors it contains
fields needed to implement certain language features such as the flat address
aperture bases. It also contains fields used by CP such as managing the
allocation of scratch memory.
.. _amdgpu-amdhsa-kernel-descriptor:
Kernel Descriptor
~~~~~~~~~~~~~~~~~
A kernel descriptor consists of the information needed by CP to initiate the
execution of a kernel, including the entry point address of the machine code
that implements the kernel.
Kernel Descriptor for GFX6-GFX9
+++++++++++++++++++++++++++++++
CP microcode requires the Kernel descritor to be allocated on 64 byte alignment.
.. table:: Kernel Descriptor for GFX6-GFX9
:name: amdgpu-amdhsa-kernel-descriptor-gfx6-gfx9-table
======= ======= =============================== ============================
Bits Size Field Name Description
======= ======= =============================== ============================
31:0 4 bytes GroupSegmentFixedSize The amount of fixed local
address space memory
required for a work-group
in bytes. This does not
include any dynamically
allocated local address
space memory that may be
added when the kernel is
dispatched.
63:32 4 bytes PrivateSegmentFixedSize The amount of fixed
private address space
memory required for a
work-item in bytes. If
is_dynamic_callstack is 1
then additional space must
be added to this value for
the call stack.
95:64 4 bytes MaxFlatWorkGroupSize Maximum flat work-group
size supported by the
kernel in work-items.
96 1 bit IsDynamicCallStack Indicates if the generated
machine code is using a
dynamically sized call
stack.
97 1 bit IsXNACKEnabled Indicates if the generated
machine code is capable of
suppoting XNACK.
127:98 30 bits Reserved, must be 0.
191:128 8 bytes KernelCodeEntryByteOffset Byte offset (possibly
negative) from base
address of kernel
descriptor to kernel's
entry point instruction
which must be 256 byte
aligned.
383:192 24 Reserved, must be 0.
bytes
415:384 4 bytes ComputePgmRsrc1 Compute Shader (CS)
program settings used by
CP to set up
``COMPUTE_PGM_RSRC1``
configuration
register. See
:ref:`amdgpu-amdhsa-compute_pgm_rsrc1-gfx6-gfx9-table`.
447:416 4 bytes ComputePgmRsrc2 Compute Shader (CS)
program settings used by
CP to set up
``COMPUTE_PGM_RSRC2``
configuration
register. See
:ref:`amdgpu-amdhsa-compute_pgm_rsrc2-gfx6-gfx9-table`.
448 1 bit EnableSGPRPrivateSegmentBuffer Enable the setup of the
SGPR user data registers
(see
:ref:`amdgpu-amdhsa-initial-kernel-execution-state`).
The total number of SGPR
user data registers
requested must not exceed
16 and match value in
``compute_pgm_rsrc2.user_sgpr.user_sgpr_count``.
Any requests beyond 16
will be ignored.
449 1 bit EnableSGPRDispatchPtr *see above*
450 1 bit EnableSGPRQueuePtr *see above*
451 1 bit EnableSGPRKernargSegmentPtr *see above*
452 1 bit EnableSGPRDispatchID *see above*
453 1 bit EnableSGPRFlatScratchInit *see above*
454 1 bit EnableSGPRPrivateSegmentSize *see above*
455 1 bit EnableSGPRGridWorkgroupCountX Not implemented in CP and
should always be 0.
456 1 bit EnableSGPRGridWorkgroupCountY Not implemented in CP and
should always be 0.
457 1 bit EnableSGPRGridWorkgroupCountZ Not implemented in CP and
should always be 0.
463:458 6 bits Reserved, must be 0.
511:464 6 Reserved, must be 0.
bytes
512 **Total size 64 bytes.**
======= ====================================================================
..
.. table:: compute_pgm_rsrc1 for GFX6-GFX9
:name: amdgpu-amdhsa-compute_pgm_rsrc1-gfx6-gfx9-table
======= ======= =============================== ===========================================================================
Bits Size Field Name Description
======= ======= =============================== ===========================================================================
5:0 6 bits GRANULATED_WORKITEM_VGPR_COUNT Number of vector registers
used by each work-item,
granularity is device
specific:
GFX6-9
- max_vgpr 1..256
- roundup((max_vgpg + 1)
/ 4) - 1
Used by CP to set up
``COMPUTE_PGM_RSRC1.VGPRS``.
9:6 4 bits GRANULATED_WAVEFRONT_SGPR_COUNT Number of scalar registers
used by a wavefront,
granularity is device
specific:
GFX6-8
- max_sgpr 1..112
- roundup((max_sgpg + 1)
/ 8) - 1
GFX9
- max_sgpr 1..112
- roundup((max_sgpg + 1)
/ 16) - 1
Includes the special SGPRs
for VCC, Flat Scratch (for
GFX7 onwards) and XNACK
(for GFX8 onwards). It does
not include the 16 SGPR
added if a trap handler is
enabled.
Used by CP to set up
``COMPUTE_PGM_RSRC1.SGPRS``.
11:10 2 bits PRIORITY Must be 0.
Start executing wavefront
at the specified priority.
CP is responsible for
filling in
``COMPUTE_PGM_RSRC1.PRIORITY``.
13:12 2 bits FLOAT_ROUND_MODE_32 Wavefront starts execution
with specified rounding
mode for single (32
bit) floating point
precision floating point
operations.
Floating point rounding
mode values are defined in
:ref:`amdgpu-amdhsa-floating-point-rounding-mode-enumeration-values-table`.
Used by CP to set up
``COMPUTE_PGM_RSRC1.FLOAT_MODE``.
15:14 2 bits FLOAT_ROUND_MODE_16_64 Wavefront starts execution
with specified rounding
denorm mode for half/double (16
and 64 bit) floating point
precision floating point
operations.
Floating point rounding
mode values are defined in
:ref:`amdgpu-amdhsa-floating-point-rounding-mode-enumeration-values-table`.
Used by CP to set up
``COMPUTE_PGM_RSRC1.FLOAT_MODE``.
17:16 2 bits FLOAT_DENORM_MODE_32 Wavefront starts execution
with specified denorm mode
for single (32
bit) floating point
precision floating point
operations.
Floating point denorm mode
values are defined in
:ref:`amdgpu-amdhsa-floating-point-denorm-mode-enumeration-values-table`.
Used by CP to set up
``COMPUTE_PGM_RSRC1.FLOAT_MODE``.
19:18 2 bits FLOAT_DENORM_MODE_16_64 Wavefront starts execution
with specified denorm mode
for half/double (16
and 64 bit) floating point
precision floating point
operations.
Floating point denorm mode
values are defined in
:ref:`amdgpu-amdhsa-floating-point-denorm-mode-enumeration-values-table`.
Used by CP to set up
``COMPUTE_PGM_RSRC1.FLOAT_MODE``.
20 1 bit PRIV Must be 0.
Start executing wavefront
in privilege trap handler
mode.
CP is responsible for
filling in
``COMPUTE_PGM_RSRC1.PRIV``.
21 1 bit ENABLE_DX10_CLAMP Wavefront starts execution
with DX10 clamp mode
enabled. Used by the vector
ALU to force DX10 style
treatment of NaN's (when
set, clamp NaN to zero,
otherwise pass NaN
through).
Used by CP to set up
``COMPUTE_PGM_RSRC1.DX10_CLAMP``.
22 1 bit DEBUG_MODE Must be 0.
Start executing wavefront
in single step mode.
CP is responsible for
filling in
``COMPUTE_PGM_RSRC1.DEBUG_MODE``.
23 1 bit ENABLE_IEEE_MODE Wavefront starts execution
with IEEE mode
enabled. Floating point
opcodes that support
exception flag gathering
will quiet and propagate
signaling-NaN inputs per
IEEE 754-2008. Min_dx10 and
max_dx10 become IEEE
754-2008 compliant due to
signaling-NaN propagation
and quieting.
Used by CP to set up
``COMPUTE_PGM_RSRC1.IEEE_MODE``.
24 1 bit BULKY Must be 0.
Only one work-group allowed
to execute on a compute
unit.
CP is responsible for
filling in
``COMPUTE_PGM_RSRC1.BULKY``.
25 1 bit CDBG_USER Must be 0.
Flag that can be used to
control debugging code.
CP is responsible for
filling in
``COMPUTE_PGM_RSRC1.CDBG_USER``.
26 1 bit FP16_OVFL GFX6-8
Reserved, must be 0.
GFX9
Wavefront starts execution
with specified fp16 overflow
mode.
- If 0, fp16 overflow generates
+/-INF values.
- If 1, fp16 overflow that is the
result of an +/-INF input value
or divide by 0 produces a +/-INF,
otherwise clamps computed
overflow to +/-MAX_FP16 as
appropriate.
Used by CP to set up
``COMPUTE_PGM_RSRC1.FP16_OVFL``.
31:27 5 bits Reserved, must be 0.
32 **Total size 4 bytes**
======= ===================================================================================================================
..
.. table:: compute_pgm_rsrc2 for GFX6-GFX9
:name: amdgpu-amdhsa-compute_pgm_rsrc2-gfx6-gfx9-table
======= ======= =============================== ===========================================================================
Bits Size Field Name Description
======= ======= =============================== ===========================================================================
0 1 bit ENABLE_SGPR_PRIVATE_SEGMENT Enable the setup of the
_WAVE_OFFSET SGPR wave scratch offset
system register (see
:ref:`amdgpu-amdhsa-initial-kernel-execution-state`).
Used by CP to set up
``COMPUTE_PGM_RSRC2.SCRATCH_EN``.
5:1 5 bits USER_SGPR_COUNT The total number of SGPR
user data registers
requested. This number must
match the number of user
data registers enabled.
Used by CP to set up
``COMPUTE_PGM_RSRC2.USER_SGPR``.
6 1 bit ENABLE_TRAP_HANDLER Set to 1 if code contains a
TRAP instruction which
requires a trap handler to
be enabled.
CP sets
``COMPUTE_PGM_RSRC2.TRAP_PRESENT``
if the runtime has
installed a trap handler
regardless of the setting
of this field.
7 1 bit ENABLE_SGPR_WORKGROUP_ID_X Enable the setup of the
system SGPR register for
the work-group id in the X
dimension (see
:ref:`amdgpu-amdhsa-initial-kernel-execution-state`).
Used by CP to set up
``COMPUTE_PGM_RSRC2.TGID_X_EN``.
8 1 bit ENABLE_SGPR_WORKGROUP_ID_Y Enable the setup of the
system SGPR register for
the work-group id in the Y
dimension (see
:ref:`amdgpu-amdhsa-initial-kernel-execution-state`).
Used by CP to set up
``COMPUTE_PGM_RSRC2.TGID_Y_EN``.
9 1 bit ENABLE_SGPR_WORKGROUP_ID_Z Enable the setup of the
system SGPR register for
the work-group id in the Z
dimension (see
:ref:`amdgpu-amdhsa-initial-kernel-execution-state`).
Used by CP to set up
``COMPUTE_PGM_RSRC2.TGID_Z_EN``.
10 1 bit ENABLE_SGPR_WORKGROUP_INFO Enable the setup of the
system SGPR register for
work-group information (see
:ref:`amdgpu-amdhsa-initial-kernel-execution-state`).
Used by CP to set up
``COMPUTE_PGM_RSRC2.TGID_SIZE_EN``.
12:11 2 bits ENABLE_VGPR_WORKITEM_ID Enable the setup of the
VGPR system registers used
for the work-item ID.
:ref:`amdgpu-amdhsa-system-vgpr-work-item-id-enumeration-values-table`
defines the values.
Used by CP to set up
``COMPUTE_PGM_RSRC2.TIDIG_CMP_CNT``.
13 1 bit ENABLE_EXCEPTION_ADDRESS_WATCH Must be 0.
Wavefront starts execution
with address watch
exceptions enabled which
are generated when L1 has
witnessed a thread access
an *address of
interest*.
CP is responsible for
filling in the address
watch bit in
``COMPUTE_PGM_RSRC2.EXCP_EN_MSB``
according to what the
runtime requests.
14 1 bit ENABLE_EXCEPTION_MEMORY Must be 0.
Wavefront starts execution
with memory violation
exceptions exceptions
enabled which are generated
when a memory violation has
occurred for this wave from
L1 or LDS
(write-to-read-only-memory,
mis-aligned atomic, LDS
address out of range,
illegal address, etc.).
CP sets the memory
violation bit in
``COMPUTE_PGM_RSRC2.EXCP_EN_MSB``
according to what the
runtime requests.
23:15 9 bits GRANULATED_LDS_SIZE Must be 0.
CP uses the rounded value
from the dispatch packet,
not this value, as the
dispatch may contain
dynamically allocated group
segment memory. CP writes
directly to
``COMPUTE_PGM_RSRC2.LDS_SIZE``.
Amount of group segment
(LDS) to allocate for each
work-group. Granularity is
device specific:
GFX6:
roundup(lds-size / (64 * 4))
GFX7-GFX9:
roundup(lds-size / (128 * 4))
24 1 bit ENABLE_EXCEPTION_IEEE_754_FP Wavefront starts execution
_INVALID_OPERATION with specified exceptions
enabled.
Used by CP to set up
``COMPUTE_PGM_RSRC2.EXCP_EN``
(set from bits 0..6).
IEEE 754 FP Invalid
Operation
25 1 bit ENABLE_EXCEPTION_FP_DENORMAL FP Denormal one or more
_SOURCE input operands is a
denormal number
26 1 bit ENABLE_EXCEPTION_IEEE_754_FP IEEE 754 FP Division by
_DIVISION_BY_ZERO Zero
27 1 bit ENABLE_EXCEPTION_IEEE_754_FP IEEE 754 FP FP Overflow
_OVERFLOW
28 1 bit ENABLE_EXCEPTION_IEEE_754_FP IEEE 754 FP Underflow
_UNDERFLOW
29 1 bit ENABLE_EXCEPTION_IEEE_754_FP IEEE 754 FP Inexact
_INEXACT
30 1 bit ENABLE_EXCEPTION_INT_DIVIDE_BY Integer Division by Zero
_ZERO (rcp_iflag_f32 instruction
only)
31 1 bit Reserved, must be 0.
32 **Total size 4 bytes.**
======= ===================================================================================================================
..
.. table:: Floating Point Rounding Mode Enumeration Values
:name: amdgpu-amdhsa-floating-point-rounding-mode-enumeration-values-table
====================================== ===== ==============================
Enumeration Name Value Description
====================================== ===== ==============================
AMDGPU_FLOAT_ROUND_MODE_NEAR_EVEN 0 Round Ties To Even
AMDGPU_FLOAT_ROUND_MODE_PLUS_INFINITY 1 Round Toward +infinity
AMDGPU_FLOAT_ROUND_MODE_MINUS_INFINITY 2 Round Toward -infinity
AMDGPU_FLOAT_ROUND_MODE_ZERO 3 Round Toward 0
====================================== ===== ==============================
..
.. table:: Floating Point Denorm Mode Enumeration Values
:name: amdgpu-amdhsa-floating-point-denorm-mode-enumeration-values-table
====================================== ===== ==============================
Enumeration Name Value Description
====================================== ===== ==============================
AMDGPU_FLOAT_DENORM_MODE_FLUSH_SRC_DST 0 Flush Source and Destination
Denorms
AMDGPU_FLOAT_DENORM_MODE_FLUSH_DST 1 Flush Output Denorms
AMDGPU_FLOAT_DENORM_MODE_FLUSH_SRC 2 Flush Source Denorms
AMDGPU_FLOAT_DENORM_MODE_FLUSH_NONE 3 No Flush
====================================== ===== ==============================
..
.. table:: System VGPR Work-Item ID Enumeration Values
:name: amdgpu-amdhsa-system-vgpr-work-item-id-enumeration-values-table
======================================== ===== ============================
Enumeration Name Value Description
======================================== ===== ============================
AMDGPU_SYSTEM_VGPR_WORKITEM_ID_X 0 Set work-item X dimension
ID.
AMDGPU_SYSTEM_VGPR_WORKITEM_ID_X_Y 1 Set work-item X and Y
dimensions ID.
AMDGPU_SYSTEM_VGPR_WORKITEM_ID_X_Y_Z 2 Set work-item X, Y and Z
dimensions ID.
AMDGPU_SYSTEM_VGPR_WORKITEM_ID_UNDEFINED 3 Undefined.
======================================== ===== ============================
.. _amdgpu-amdhsa-initial-kernel-execution-state:
Initial Kernel Execution State
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
This section defines the register state that will be set up by the packet
processor prior to the start of execution of every wavefront. This is limited by
the constraints of the hardware controllers of CP/ADC/SPI.
The order of the SGPR registers is defined, but the compiler can specify which
ones are actually setup in the kernel descriptor using the ``enable_sgpr_*`` bit
fields (see :ref:`amdgpu-amdhsa-kernel-descriptor`). The register numbers used
for enabled registers are dense starting at SGPR0: the first enabled register is
SGPR0, the next enabled register is SGPR1 etc.; disabled registers do not have
an SGPR number.
The initial SGPRs comprise up to 16 User SRGPs that are set by CP and apply to
all waves of the grid. It is possible to specify more than 16 User SGPRs using
the ``enable_sgpr_*`` bit fields, in which case only the first 16 are actually
initialized. These are then immediately followed by the System SGPRs that are
set up by ADC/SPI and can have different values for each wave of the grid
dispatch.
SGPR register initial state is defined in
:ref:`amdgpu-amdhsa-sgpr-register-set-up-order-table`.
.. table:: SGPR Register Set Up Order
:name: amdgpu-amdhsa-sgpr-register-set-up-order-table
========== ========================== ====== ==============================
SGPR Order Name Number Description
(kernel descriptor enable of
field) SGPRs
========== ========================== ====== ==============================
First Private Segment Buffer 4 V# that can be used, together
(enable_sgpr_private with Scratch Wave Offset as an
_segment_buffer) offset, to access the private
memory space using a segment
address.
CP uses the value provided by
the runtime.
then Dispatch Ptr 2 64 bit address of AQL dispatch
(enable_sgpr_dispatch_ptr) packet for kernel dispatch
actually executing.
then Queue Ptr 2 64 bit address of amd_queue_t
(enable_sgpr_queue_ptr) object for AQL queue on which
the dispatch packet was
queued.
then Kernarg Segment Ptr 2 64 bit address of Kernarg
(enable_sgpr_kernarg segment. This is directly
_segment_ptr) copied from the
kernarg_address in the kernel
dispatch packet.
Having CP load it once avoids
loading it at the beginning of
every wavefront.
then Dispatch Id 2 64 bit Dispatch ID of the
(enable_sgpr_dispatch_id) dispatch packet being
executed.
then Flat Scratch Init 2 This is 2 SGPRs:
(enable_sgpr_flat_scratch
_init) GFX6
Not supported.
GFX7-GFX8
The first SGPR is a 32 bit
byte offset from
``SH_HIDDEN_PRIVATE_BASE_VIMID``
to per SPI base of memory
for scratch for the queue
executing the kernel
dispatch. CP obtains this
from the runtime. (The
Scratch Segment Buffer base
address is
``SH_HIDDEN_PRIVATE_BASE_VIMID``
plus this offset.) The value
of Scratch Wave Offset must
be added to this offset by
the kernel machine code,
right shifted by 8, and
moved to the FLAT_SCRATCH_HI
SGPR register.
FLAT_SCRATCH_HI corresponds
to SGPRn-4 on GFX7, and
SGPRn-6 on GFX8 (where SGPRn
is the highest numbered SGPR
allocated to the wave).
FLAT_SCRATCH_HI is
multiplied by 256 (as it is
in units of 256 bytes) and
added to
``SH_HIDDEN_PRIVATE_BASE_VIMID``
to calculate the per wave
FLAT SCRATCH BASE in flat
memory instructions that
access the scratch
apperture.
The second SGPR is 32 bit
byte size of a single
work-item's scratch memory
usage. CP obtains this from
the runtime, and it is
always a multiple of DWORD.
CP checks that the value in
the kernel dispatch packet
Private Segment Byte Size is
not larger, and requests the
runtime to increase the
queue's scratch size if
necessary. The kernel code
must move it to
FLAT_SCRATCH_LO which is
SGPRn-3 on GFX7 and SGPRn-5
on GFX8. FLAT_SCRATCH_LO is
used as the FLAT SCRATCH
SIZE in flat memory
instructions. Having CP load
it once avoids loading it at
the beginning of every
wavefront. GFX9 This is the
64 bit base address of the
per SPI scratch backing
memory managed by SPI for
the queue executing the
kernel dispatch. CP obtains
this from the runtime (and
divides it if there are
multiple Shader Arrays each
with its own SPI). The value
of Scratch Wave Offset must
be added by the kernel
machine code and the result
moved to the FLAT_SCRATCH
SGPR which is SGPRn-6 and
SGPRn-5. It is used as the
FLAT SCRATCH BASE in flat
memory instructions. then
Private Segment Size 1 The
32 bit byte size of a
(enable_sgpr_private single
work-item's
scratch_segment_size) memory
allocation. This is the
value from the kernel
dispatch packet Private
Segment Byte Size rounded up
by CP to a multiple of
DWORD.
Having CP load it once avoids
loading it at the beginning of
every wavefront.
This is not used for
GFX7-GFX8 since it is the same
value as the second SGPR of
Flat Scratch Init. However, it
may be needed for GFX9 which
changes the meaning of the
Flat Scratch Init value.
then Grid Work-Group Count X 1 32 bit count of the number of
(enable_sgpr_grid work-groups in the X dimension
_workgroup_count_X) for the grid being
executed. Computed from the
fields in the kernel dispatch
packet as ((grid_size.x +
workgroup_size.x - 1) /
workgroup_size.x).
then Grid Work-Group Count Y 1 32 bit count of the number of
(enable_sgpr_grid work-groups in the Y dimension
_workgroup_count_Y && for the grid being
less than 16 previous executed. Computed from the
SGPRs) fields in the kernel dispatch
packet as ((grid_size.y +
workgroup_size.y - 1) /
workgroupSize.y).
Only initialized if <16
previous SGPRs initialized.
then Grid Work-Group Count Z 1 32 bit count of the number of
(enable_sgpr_grid work-groups in the Z dimension
_workgroup_count_Z && for the grid being
less than 16 previous executed. Computed from the
SGPRs) fields in the kernel dispatch
packet as ((grid_size.z +
workgroup_size.z - 1) /
workgroupSize.z).
Only initialized if <16
previous SGPRs initialized.
then Work-Group Id X 1 32 bit work-group id in X
(enable_sgpr_workgroup_id dimension of grid for
_X) wavefront.
then Work-Group Id Y 1 32 bit work-group id in Y
(enable_sgpr_workgroup_id dimension of grid for
_Y) wavefront.
then Work-Group Id Z 1 32 bit work-group id in Z
(enable_sgpr_workgroup_id dimension of grid for
_Z) wavefront.
then Work-Group Info 1 {first_wave, 14'b0000,
(enable_sgpr_workgroup ordered_append_term[10:0],
_info) threadgroup_size_in_waves[5:0]}
then Scratch Wave Offset 1 32 bit byte offset from base
(enable_sgpr_private of scratch base of queue
_segment_wave_offset) executing the kernel
dispatch. Must be used as an
offset with Private
segment address when using
Scratch Segment Buffer. It
must be used to set up FLAT
SCRATCH for flat addressing
(see
:ref:`amdgpu-amdhsa-flat-scratch`).
========== ========================== ====== ==============================
The order of the VGPR registers is defined, but the compiler can specify which
ones are actually setup in the kernel descriptor using the ``enable_vgpr*`` bit
fields (see :ref:`amdgpu-amdhsa-kernel-descriptor`). The register numbers used
for enabled registers are dense starting at VGPR0: the first enabled register is
VGPR0, the next enabled register is VGPR1 etc.; disabled registers do not have a
VGPR number.
VGPR register initial state is defined in
:ref:`amdgpu-amdhsa-vgpr-register-set-up-order-table`.
.. table:: VGPR Register Set Up Order
:name: amdgpu-amdhsa-vgpr-register-set-up-order-table
========== ========================== ====== ==============================
VGPR Order Name Number Description
(kernel descriptor enable of
field) VGPRs
========== ========================== ====== ==============================
First Work-Item Id X 1 32 bit work item id in X
(Always initialized) dimension of work-group for
wavefront lane.
then Work-Item Id Y 1 32 bit work item id in Y
(enable_vgpr_workitem_id dimension of work-group for
> 0) wavefront lane.
then Work-Item Id Z 1 32 bit work item id in Z
(enable_vgpr_workitem_id dimension of work-group for
> 1) wavefront lane.
========== ========================== ====== ==============================
The setting of registers is is done by GPU CP/ADC/SPI hardware as follows:
1. SGPRs before the Work-Group Ids are set by CP using the 16 User Data
registers.
2. Work-group Id registers X, Y, Z are set by ADC which supports any
combination including none.
3. Scratch Wave Offset is set by SPI in a per wave basis which is why its value
cannot included with the flat scratch init value which is per queue.
4. The VGPRs are set by SPI which only supports specifying either (X), (X, Y)
or (X, Y, Z).
Flat Scratch register pair are adjacent SGRRs so they can be moved as a 64 bit
value to the hardware required SGPRn-3 and SGPRn-4 respectively.
The global segment can be accessed either using buffer instructions (GFX6 which
has V# 64 bit address support), flat instructions (GFX7-9), or global
instructions (GFX9).
If buffer operations are used then the compiler can generate a V# with the
following properties:
* base address of 0
* no swizzle
* ATC: 1 if IOMMU present (such as APU)
* ptr64: 1
* MTYPE set to support memory coherence that matches the runtime (such as CC for
APU and NC for dGPU).
.. _amdgpu-amdhsa-kernel-prolog:
Kernel Prolog
~~~~~~~~~~~~~
.. _amdgpu-amdhsa-m0:
M0
++
GFX6-GFX8
The M0 register must be initialized with a value at least the total LDS size
if the kernel may access LDS via DS or flat operations. Total LDS size is
available in dispatch packet. For M0, it is also possible to use maximum
possible value of LDS for given target (0x7FFF for GFX6 and 0xFFFF for
GFX7-GFX8).
GFX9
The M0 register is not used for range checking LDS accesses and so does not
need to be initialized in the prolog.
.. _amdgpu-amdhsa-flat-scratch:
Flat Scratch
++++++++++++
If the kernel may use flat operations to access scratch memory, the prolog code
must set up FLAT_SCRATCH register pair (FLAT_SCRATCH_LO/FLAT_SCRATCH_HI which
are in SGPRn-4/SGPRn-3). Initialization uses Flat Scratch Init and Scratch Wave
Offset SGPR registers (see :ref:`amdgpu-amdhsa-initial-kernel-execution-state`):
GFX6
Flat scratch is not supported.
GFX7-8
1. The low word of Flat Scratch Init is 32 bit byte offset from
``SH_HIDDEN_PRIVATE_BASE_VIMID`` to the base of scratch backing memory
being managed by SPI for the queue executing the kernel dispatch. This is
the same value used in the Scratch Segment Buffer V# base address. The
prolog must add the value of Scratch Wave Offset to get the wave's byte
scratch backing memory offset from ``SH_HIDDEN_PRIVATE_BASE_VIMID``. Since
FLAT_SCRATCH_LO is in units of 256 bytes, the offset must be right shifted
by 8 before moving into FLAT_SCRATCH_LO.
2. The second word of Flat Scratch Init is 32 bit byte size of a single
work-items scratch memory usage. This is directly loaded from the kernel
dispatch packet Private Segment Byte Size and rounded up to a multiple of
DWORD. Having CP load it once avoids loading it at the beginning of every
wavefront. The prolog must move it to FLAT_SCRATCH_LO for use as FLAT SCRATCH
SIZE.
GFX9
The Flat Scratch Init is the 64 bit address of the base of scratch backing
memory being managed by SPI for the queue executing the kernel dispatch. The
prolog must add the value of Scratch Wave Offset and moved to the FLAT_SCRATCH
pair for use as the flat scratch base in flat memory instructions.
.. _amdgpu-amdhsa-memory-model:
Memory Model
~~~~~~~~~~~~
This section describes the mapping of LLVM memory model onto AMDGPU machine code
(see :ref:`memmodel`). *The implementation is WIP.*
.. TODO
Update when implementation complete.
The AMDGPU backend supports the memory synchronization scopes specified in
:ref:`amdgpu-memory-scopes`.
The code sequences used to implement the memory model are defined in table
:ref:`amdgpu-amdhsa-memory-model-code-sequences-gfx6-gfx9-table`.
The sequences specify the order of instructions that a single thread must
execute. The ``s_waitcnt`` and ``buffer_wbinvl1_vol`` are defined with respect
to other memory instructions executed by the same thread. This allows them to be
moved earlier or later which can allow them to be combined with other instances
of the same instruction, or hoisted/sunk out of loops to improve
performance. Only the instructions related to the memory model are given;
additional ``s_waitcnt`` instructions are required to ensure registers are
defined before being used. These may be able to be combined with the memory
model ``s_waitcnt`` instructions as described above.
The AMDGPU backend supports the following memory models:
HSA Memory Model [HSA]_
The HSA memory model uses a single happens-before relation for all address
spaces (see :ref:`amdgpu-address-spaces`).
OpenCL Memory Model [OpenCL]_
The OpenCL memory model which has separate happens-before relations for the
global and local address spaces. Only a fence specifying both global and
local address space, and seq_cst instructions join the relationships. Since
the LLVM ``memfence`` instruction does not allow an address space to be
specified the OpenCL fence has to convervatively assume both local and
global address space was specified. However, optimizations can often be
done to eliminate the additional ``s_waitcnt`` instructions when there are
no intervening memory instructions which access the corresponding address
space. The code sequences in the table indicate what can be omitted for the
OpenCL memory. The target triple environment is used to determine if the
source language is OpenCL (see :ref:`amdgpu-opencl`).
``ds/flat_load/store/atomic`` instructions to local memory are termed LDS
operations.
``buffer/global/flat_load/store/atomic`` instructions to global memory are
termed vector memory operations.
For GFX6-GFX9:
* Each agent has multiple compute units (CU).
* Each CU has multiple SIMDs that execute wavefronts.
* The wavefronts for a single work-group are executed in the same CU but may be
executed by different SIMDs.
* Each CU has a single LDS memory shared by the wavefronts of the work-groups
executing on it.
* All LDS operations of a CU are performed as wavefront wide operations in a
global order and involve no caching. Completion is reported to a wavefront in
execution order.
* The LDS memory has multiple request queues shared by the SIMDs of a
CU. Therefore, the LDS operations performed by different waves of a work-group
can be reordered relative to each other, which can result in reordering the
visibility of vector memory operations with respect to LDS operations of other
wavefronts in the same work-group. A ``s_waitcnt lgkmcnt(0)`` is required to
ensure synchronization between LDS operations and vector memory operations
between waves of a work-group, but not between operations performed by the
same wavefront.
* The vector memory operations are performed as wavefront wide operations and
completion is reported to a wavefront in execution order. The exception is
that for GFX7-9 ``flat_load/store/atomic`` instructions can report out of
vector memory order if they access LDS memory, and out of LDS operation order
if they access global memory.
* The vector memory operations access a single vector L1 cache shared by all
SIMDs a CU. Therefore, no special action is required for coherence between the
lanes of a single wavefront, or for coherence between wavefronts in the same
work-group. A ``buffer_wbinvl1_vol`` is required for coherence between waves
executing in different work-groups as they may be executing on different CUs.
* The scalar memory operations access a scalar L1 cache shared by all wavefronts
on a group of CUs. The scalar and vector L1 caches are not coherent. However,
scalar operations are used in a restricted way so do not impact the memory
model. See :ref:`amdgpu-amdhsa-memory-spaces`.
* The vector and scalar memory operations use an L2 cache shared by all CUs on
the same agent.
* The L2 cache has independent channels to service disjoint ranges of virtual
addresses.
* Each CU has a separate request queue per channel. Therefore, the vector and
scalar memory operations performed by waves executing in different work-groups
(which may be executing on different CUs) of an agent can be reordered
relative to each other. A ``s_waitcnt vmcnt(0)`` is required to ensure
synchronization between vector memory operations of different CUs. It ensures a
previous vector memory operation has completed before executing a subsequent
vector memory or LDS operation and so can be used to meet the requirements of
acquire and release.
* The L2 cache can be kept coherent with other agents on some targets, or ranges
of virtual addresses can be set up to bypass it to ensure system coherence.
Private address space uses ``buffer_load/store`` using the scratch V# (GFX6-8),
or ``scratch_load/store`` (GFX9). Since only a single thread is accessing the
memory, atomic memory orderings are not meaningful and all accesses are treated
as non-atomic.
Constant address space uses ``buffer/global_load`` instructions (or equivalent
scalar memory instructions). Since the constant address space contents do not
change during the execution of a kernel dispatch it is not legal to perform
stores, and atomic memory orderings are not meaningful and all access are
treated as non-atomic.
A memory synchronization scope wider than work-group is not meaningful for the
group (LDS) address space and is treated as work-group.
The memory model does not support the region address space which is treated as
non-atomic.
Acquire memory ordering is not meaningful on store atomic instructions and is
treated as non-atomic.
Release memory ordering is not meaningful on load atomic instructions and is
treated a non-atomic.
Acquire-release memory ordering is not meaningful on load or store atomic
instructions and is treated as acquire and release respectively.
AMDGPU backend only uses scalar memory operations to access memory that is
proven to not change during the execution of the kernel dispatch. This includes
constant address space and global address space for program scope const
variables. Therefore the kernel machine code does not have to maintain the
scalar L1 cache to ensure it is coherent with the vector L1 cache. The scalar
and vector L1 caches are invalidated between kernel dispatches by CP since
constant address space data may change between kernel dispatch executions. See
:ref:`amdgpu-amdhsa-memory-spaces`.
The one execption is if scalar writes are used to spill SGPR registers. In this
case the AMDGPU backend ensures the memory location used to spill is never
accessed by vector memory operations at the same time. If scalar writes are used
then a ``s_dcache_wb`` is inserted before the ``s_endpgm`` and before a function
return since the locations may be used for vector memory instructions by a
future wave that uses the same scratch area, or a function call that creates a
frame at the same address, respectively. There is no need for a ``s_dcache_inv``
as all scalar writes are write-before-read in the same thread.
Scratch backing memory (which is used for the private address space)
is accessed with MTYPE NC_NV (non-coherenent non-volatile). Since the private
address space is only accessed by a single thread, and is always
write-before-read, there is never a need to invalidate these entries from the L1
cache. Hence all cache invalidates are done as ``*_vol`` to only invalidate the
volatile cache lines.
On dGPU the kernarg backing memory is accessed as UC (uncached) to avoid needing
to invalidate the L2 cache. This also causes it to be treated as
non-volatile and so is not invalidated by ``*_vol``. On APU it is accessed as CC
(cache coherent) and so the L2 cache will coherent with the CPU and other
agents.
.. table:: AMDHSA Memory Model Code Sequences GFX6-GFX9
:name: amdgpu-amdhsa-memory-model-code-sequences-gfx6-gfx9-table
============ ============ ============== ========== ===============================
LLVM Instr LLVM Memory LLVM Memory AMDGPU AMDGPU Machine Code
Ordering Sync Scope Address
Space
============ ============ ============== ========== ===============================
**Non-Atomic**
-----------------------------------------------------------------------------------
load *none* *none* - global - !volatile & !nontemporal
- generic
- private 1. buffer/global/flat_load
- constant
- volatile & !nontemporal
1. buffer/global/flat_load
glc=1
- nontemporal
1. buffer/global/flat_load
glc=1 slc=1
load *none* *none* - local 1. ds_load
store *none* *none* - global - !nontemporal
- generic
- private 1. buffer/global/flat_store
- constant
- nontemporal
1. buffer/global/flat_stote
glc=1 slc=1
store *none* *none* - local 1. ds_store
**Unordered Atomic**
-----------------------------------------------------------------------------------
load atomic unordered *any* *any* *Same as non-atomic*.
store atomic unordered *any* *any* *Same as non-atomic*.
atomicrmw unordered *any* *any* *Same as monotonic
atomic*.
**Monotonic Atomic**
-----------------------------------------------------------------------------------
load atomic monotonic - singlethread - global 1. buffer/global/flat_load
- wavefront - generic
- workgroup
load atomic monotonic - singlethread - local 1. ds_load
- wavefront
- workgroup
load atomic monotonic - agent - global 1. buffer/global/flat_load
- system - generic glc=1
store atomic monotonic - singlethread - global 1. buffer/global/flat_store
- wavefront - generic
- workgroup
- agent
- system
store atomic monotonic - singlethread - local 1. ds_store
- wavefront
- workgroup
atomicrmw monotonic - singlethread - global 1. buffer/global/flat_atomic
- wavefront - generic
- workgroup
- agent
- system
atomicrmw monotonic - singlethread - local 1. ds_atomic
- wavefront
- workgroup
**Acquire Atomic**
-----------------------------------------------------------------------------------
load atomic acquire - singlethread - global 1. buffer/global/ds/flat_load
- wavefront - local
- generic
load atomic acquire - workgroup - global 1. buffer/global/flat_load
load atomic acquire - workgroup - local 1. ds_load
2. s_waitcnt lgkmcnt(0)
- If OpenCL, omit.
- Must happen before
any following
global/generic
load/load
atomic/store/store
atomic/atomicrmw.
- Ensures any
following global
data read is no
older than the load
atomic value being
acquired.
load atomic acquire - workgroup - generic 1. flat_load
2. s_waitcnt lgkmcnt(0)
- If OpenCL, omit.
- Must happen before
any following
global/generic
load/load
atomic/store/store
atomic/atomicrmw.
- Ensures any
following global
data read is no
older than the load
atomic value being
acquired.
load atomic acquire - agent - global 1. buffer/global/flat_load
- system glc=1
2. s_waitcnt vmcnt(0)
- Must happen before
following
buffer_wbinvl1_vol.
- Ensures the load
has completed
before invalidating
the cache.
3. buffer_wbinvl1_vol
- Must happen before
any following
global/generic
load/load
atomic/atomicrmw.
- Ensures that
following
loads will not see
stale global data.
load atomic acquire - agent - generic 1. flat_load glc=1
- system 2. s_waitcnt vmcnt(0) &
lgkmcnt(0)
- If OpenCL omit
lgkmcnt(0).
- Must happen before
following
buffer_wbinvl1_vol.
- Ensures the flat_load
has completed
before invalidating
the cache.
3. buffer_wbinvl1_vol
- Must happen before
any following
global/generic
load/load
atomic/atomicrmw.
- Ensures that
following loads
will not see stale
global data.
atomicrmw acquire - singlethread - global 1. buffer/global/ds/flat_atomic
- wavefront - local
- generic
atomicrmw acquire - workgroup - global 1. buffer/global/flat_atomic
atomicrmw acquire - workgroup - local 1. ds_atomic
2. waitcnt lgkmcnt(0)
- If OpenCL, omit.
- Must happen before
any following
global/generic
load/load
atomic/store/store
atomic/atomicrmw.
- Ensures any
following global
data read is no
older than the
atomicrmw value
being acquired.
atomicrmw acquire - workgroup - generic 1. flat_atomic
2. waitcnt lgkmcnt(0)
- If OpenCL, omit.
- Must happen before
any following
global/generic
load/load
atomic/store/store
atomic/atomicrmw.
- Ensures any
following global
data read is no
older than the
atomicrmw value
being acquired.
atomicrmw acquire - agent - global 1. buffer/global/flat_atomic
- system 2. s_waitcnt vmcnt(0)
- Must happen before
following
buffer_wbinvl1_vol.
- Ensures the
atomicrmw has
completed before
invalidating the
cache.
3. buffer_wbinvl1_vol
- Must happen before
any following
global/generic
load/load
atomic/atomicrmw.
- Ensures that
following loads
will not see stale
global data.
atomicrmw acquire - agent - generic 1. flat_atomic
- system 2. s_waitcnt vmcnt(0) &
lgkmcnt(0)
- If OpenCL, omit
lgkmcnt(0).
- Must happen before
following
buffer_wbinvl1_vol.
- Ensures the
atomicrmw has
completed before
invalidating the
cache.
3. buffer_wbinvl1_vol
- Must happen before
any following
global/generic
load/load
atomic/atomicrmw.
- Ensures that
following loads
will not see stale
global data.
fence acquire - singlethread *none* *none*
- wavefront
fence acquire - workgroup *none* 1. s_waitcnt lgkmcnt(0)
- If OpenCL and
address space is
not generic, omit.
- However, since LLVM
currently has no
address space on
the fence need to
conservatively
always generate. If
fence had an
address space then
set to address
space of OpenCL
fence flag, or to
generic if both
local and global
flags are
specified.
- Must happen after
any preceding
local/generic load
atomic/atomicrmw
with an equal or
wider sync scope
and memory ordering
stronger than
unordered (this is
termed the
fence-paired-atomic).
- Must happen before
any following
global/generic
load/load
atomic/store/store
atomic/atomicrmw.
- Ensures any
following global
data read is no
older than the
value read by the
fence-paired-atomic.
fence acquire - agent *none* 1. s_waitcnt lgkmcnt(0) &
- system vmcnt(0)
- If OpenCL and
address space is
not generic, omit
lgkmcnt(0).
- However, since LLVM
currently has no
address space on
the fence need to
conservatively
always generate
(see comment for
previous fence).
- Could be split into
separate s_waitcnt
vmcnt(0) and
s_waitcnt
lgkmcnt(0) to allow
them to be
independently moved
according to the
following rules.
- s_waitcnt vmcnt(0)
must happen after
any preceding
global/generic load
atomic/atomicrmw
with an equal or
wider sync scope
and memory ordering
stronger than
unordered (this is
termed the
fence-paired-atomic).
- s_waitcnt lgkmcnt(0)
must happen after
any preceding
local/generic load
atomic/atomicrmw
with an equal or
wider sync scope
and memory ordering
stronger than
unordered (this is
termed the
fence-paired-atomic).
- Must happen before
the following
buffer_wbinvl1_vol.
- Ensures that the
fence-paired atomic
has completed
before invalidating
the
cache. Therefore
any following
locations read must
be no older than
the value read by
the
fence-paired-atomic.
2. buffer_wbinvl1_vol
- Must happen before any
following global/generic
load/load
atomic/store/store
atomic/atomicrmw.
- Ensures that
following loads
will not see stale
global data.
**Release Atomic**
-----------------------------------------------------------------------------------
store atomic release - singlethread - global 1. buffer/global/ds/flat_store
- wavefront - local
- generic
store atomic release - workgroup - global 1. s_waitcnt lgkmcnt(0)
- If OpenCL, omit.
- Must happen after
any preceding
local/generic
load/store/load
atomic/store
atomic/atomicrmw.
- Must happen before
the following
store.
- Ensures that all
memory operations
to local have
completed before
performing the
store that is being
released.
2. buffer/global/flat_store
store atomic release - workgroup - local 1. ds_store
store atomic release - workgroup - generic 1. s_waitcnt lgkmcnt(0)
- If OpenCL, omit.
- Must happen after
any preceding
local/generic
load/store/load
atomic/store
atomic/atomicrmw.
- Must happen before
the following
store.
- Ensures that all
memory operations
to local have
completed before
performing the
store that is being
released.
2. flat_store
store atomic release - agent - global 1. s_waitcnt lgkmcnt(0) &
- system - generic vmcnt(0)
- If OpenCL, omit
lgkmcnt(0).
- Could be split into
separate s_waitcnt
vmcnt(0) and
s_waitcnt
lgkmcnt(0) to allow
them to be
independently moved
according to the
following rules.
- s_waitcnt vmcnt(0)
must happen after
any preceding
global/generic
load/store/load
atomic/store
atomic/atomicrmw.
- s_waitcnt lgkmcnt(0)
must happen after
any preceding
local/generic
load/store/load
atomic/store
atomic/atomicrmw.
- Must happen before
the following
store.
- Ensures that all
memory operations
to memory have
completed before
performing the
store that is being
released.
2. buffer/global/ds/flat_store
atomicrmw release - singlethread - global 1. buffer/global/ds/flat_atomic
- wavefront - local
- generic
atomicrmw release - workgroup - global 1. s_waitcnt lgkmcnt(0)
- If OpenCL, omit.
- Must happen after
any preceding
local/generic
load/store/load
atomic/store
atomic/atomicrmw.
- Must happen before
the following
atomicrmw.
- Ensures that all
memory operations
to local have
completed before
performing the
atomicrmw that is
being released.
2. buffer/global/flat_atomic
atomicrmw release - workgroup - local 1. ds_atomic
atomicrmw release - workgroup - generic 1. s_waitcnt lgkmcnt(0)
- If OpenCL, omit.
- Must happen after
any preceding
local/generic
load/store/load
atomic/store
atomic/atomicrmw.
- Must happen before
the following
atomicrmw.
- Ensures that all
memory operations
to local have
completed before
performing the
atomicrmw that is
being released.
2. flat_atomic
atomicrmw release - agent - global 1. s_waitcnt lgkmcnt(0) &
- system - generic vmcnt(0)
- If OpenCL, omit
lgkmcnt(0).
- Could be split into
separate s_waitcnt
vmcnt(0) and
s_waitcnt
lgkmcnt(0) to allow
them to be
independently moved
according to the
following rules.
- s_waitcnt vmcnt(0)
must happen after
any preceding
global/generic
load/store/load
atomic/store
atomic/atomicrmw.
- s_waitcnt lgkmcnt(0)
must happen after
any preceding
local/generic
load/store/load
atomic/store
atomic/atomicrmw.
- Must happen before
the following
atomicrmw.
- Ensures that all
memory operations
to global and local
have completed
before performing
the atomicrmw that
is being released.
2. buffer/global/ds/flat_atomic
fence release - singlethread *none* *none*
- wavefront
fence release - workgroup *none* 1. s_waitcnt lgkmcnt(0)
- If OpenCL and
address space is
not generic, omit.
- However, since LLVM
currently has no
address space on
the fence need to
conservatively
always generate. If
fence had an
address space then
set to address
space of OpenCL
fence flag, or to
generic if both
local and global
flags are
specified.
- Must happen after
any preceding
local/generic
load/load
atomic/store/store
atomic/atomicrmw.
- Must happen before
any following store
atomic/atomicrmw
with an equal or
wider sync scope
and memory ordering
stronger than
unordered (this is
termed the
fence-paired-atomic).
- Ensures that all
memory operations
to local have
completed before
performing the
following
fence-paired-atomic.
fence release - agent *none* 1. s_waitcnt lgkmcnt(0) &
- system vmcnt(0)
- If OpenCL and
address space is
not generic, omit
lgkmcnt(0).
- If OpenCL and
address space is
local, omit
vmcnt(0).
- However, since LLVM
currently has no
address space on
the fence need to
conservatively
always generate. If
fence had an
address space then
set to address
space of OpenCL
fence flag, or to
generic if both
local and global
flags are
specified.
- Could be split into
separate s_waitcnt
vmcnt(0) and
s_waitcnt
lgkmcnt(0) to allow
them to be
independently moved
according to the
following rules.
- s_waitcnt vmcnt(0)
must happen after
any preceding
global/generic
load/store/load
atomic/store
atomic/atomicrmw.
- s_waitcnt lgkmcnt(0)
must happen after
any preceding
local/generic
load/store/load
atomic/store
atomic/atomicrmw.
- Must happen before
any following store
atomic/atomicrmw
with an equal or
wider sync scope
and memory ordering
stronger than
unordered (this is
termed the
fence-paired-atomic).
- Ensures that all
memory operations
have
completed before
performing the
following
fence-paired-atomic.
**Acquire-Release Atomic**
-----------------------------------------------------------------------------------
atomicrmw acq_rel - singlethread - global 1. buffer/global/ds/flat_atomic
- wavefront - local
- generic
atomicrmw acq_rel - workgroup - global 1. s_waitcnt lgkmcnt(0)
- If OpenCL, omit.
- Must happen after
any preceding
local/generic
load/store/load
atomic/store
atomic/atomicrmw.
- Must happen before
the following
atomicrmw.
- Ensures that all
memory operations
to local have
completed before
performing the
atomicrmw that is
being released.
2. buffer/global/flat_atomic
atomicrmw acq_rel - workgroup - local 1. ds_atomic
2. s_waitcnt lgkmcnt(0)
- If OpenCL, omit.
- Must happen before
any following
global/generic
load/load
atomic/store/store
atomic/atomicrmw.
- Ensures any
following global
data read is no
older than the load
atomic value being
acquired.
atomicrmw acq_rel - workgroup - generic 1. s_waitcnt lgkmcnt(0)
- If OpenCL, omit.
- Must happen after
any preceding
local/generic
load/store/load
atomic/store
atomic/atomicrmw.
- Must happen before
the following
atomicrmw.
- Ensures that all
memory operations
to local have
completed before
performing the
atomicrmw that is
being released.
2. flat_atomic
3. s_waitcnt lgkmcnt(0)
- If OpenCL, omit.
- Must happen before
any following
global/generic
load/load
atomic/store/store
atomic/atomicrmw.
- Ensures any
following global
data read is no
older than the load
atomic value being
acquired.
atomicrmw acq_rel - agent - global 1. s_waitcnt lgkmcnt(0) &
- system vmcnt(0)
- If OpenCL, omit
lgkmcnt(0).
- Could be split into
separate s_waitcnt
vmcnt(0) and
s_waitcnt
lgkmcnt(0) to allow
them to be
independently moved
according to the
following rules.
- s_waitcnt vmcnt(0)
must happen after
any preceding
global/generic
load/store/load
atomic/store
atomic/atomicrmw.
- s_waitcnt lgkmcnt(0)
must happen after
any preceding
local/generic
load/store/load
atomic/store
atomic/atomicrmw.
- Must happen before
the following
atomicrmw.
- Ensures that all
memory operations
to global have
completed before
performing the
atomicrmw that is
being released.
2. buffer/global/flat_atomic
3. s_waitcnt vmcnt(0)
- Must happen before
following
buffer_wbinvl1_vol.
- Ensures the
atomicrmw has
completed before
invalidating the
cache.
4. buffer_wbinvl1_vol
- Must happen before
any following
global/generic
load/load
atomic/atomicrmw.
- Ensures that
following loads
will not see stale
global data.
atomicrmw acq_rel - agent - generic 1. s_waitcnt lgkmcnt(0) &
- system vmcnt(0)
- If OpenCL, omit
lgkmcnt(0).
- Could be split into
separate s_waitcnt
vmcnt(0) and
s_waitcnt
lgkmcnt(0) to allow
them to be
independently moved
according to the
following rules.
- s_waitcnt vmcnt(0)
must happen after
any preceding
global/generic
load/store/load
atomic/store
atomic/atomicrmw.
- s_waitcnt lgkmcnt(0)
must happen after
any preceding
local/generic
load/store/load
atomic/store
atomic/atomicrmw.
- Must happen before
the following
atomicrmw.
- Ensures that all
memory operations
to global have
completed before
performing the
atomicrmw that is
being released.
2. flat_atomic
3. s_waitcnt vmcnt(0) &
lgkmcnt(0)
- If OpenCL, omit
lgkmcnt(0).
- Must happen before
following
buffer_wbinvl1_vol.
- Ensures the
atomicrmw has
completed before
invalidating the
cache.
4. buffer_wbinvl1_vol
- Must happen before
any following
global/generic
load/load
atomic/atomicrmw.
- Ensures that
following loads
will not see stale
global data.
fence acq_rel - singlethread *none* *none*
- wavefront
fence acq_rel - workgroup *none* 1. s_waitcnt lgkmcnt(0)
- If OpenCL and
address space is
not generic, omit.
- However,
since LLVM
currently has no
address space on
the fence need to
conservatively
always generate
(see comment for
previous fence).
- Must happen after
any preceding
local/generic
load/load
atomic/store/store
atomic/atomicrmw.
- Must happen before
any following
global/generic
load/load
atomic/store/store
atomic/atomicrmw.
- Ensures that all
memory operations
to local have
completed before
performing any
following global
memory operations.
- Ensures that the
preceding
local/generic load
atomic/atomicrmw
with an equal or
wider sync scope
and memory ordering
stronger than
unordered (this is
termed the
acquire-fence-paired-atomic
) has completed
before following
global memory
operations. This
satisfies the
requirements of
acquire.
- Ensures that all
previous memory
operations have
completed before a
following
local/generic store
atomic/atomicrmw
with an equal or
wider sync scope
and memory ordering
stronger than
unordered (this is
termed the
release-fence-paired-atomic
). This satisfies the
requirements of
release.
fence acq_rel - agent *none* 1. s_waitcnt lgkmcnt(0) &
- system vmcnt(0)
- If OpenCL and
address space is
not generic, omit
lgkmcnt(0).
- However, since LLVM
currently has no
address space on
the fence need to
conservatively
always generate
(see comment for
previous fence).
- Could be split into
separate s_waitcnt
vmcnt(0) and
s_waitcnt
lgkmcnt(0) to allow
them to be
independently moved
according to the
following rules.
- s_waitcnt vmcnt(0)
must happen after
any preceding
global/generic
load/store/load
atomic/store
atomic/atomicrmw.
- s_waitcnt lgkmcnt(0)
must happen after
any preceding
local/generic
load/store/load
atomic/store
atomic/atomicrmw.
- Must happen before
the following
buffer_wbinvl1_vol.
- Ensures that the
preceding
global/local/generic
load
atomic/atomicrmw
with an equal or
wider sync scope
and memory ordering
stronger than
unordered (this is
termed the
acquire-fence-paired-atomic
) has completed
before invalidating
the cache. This
satisfies the
requirements of
acquire.
- Ensures that all
previous memory
operations have
completed before a
following
global/local/generic
store
atomic/atomicrmw
with an equal or
wider sync scope
and memory ordering
stronger than
unordered (this is
termed the
release-fence-paired-atomic
). This satisfies the
requirements of
release.
2. buffer_wbinvl1_vol
- Must happen before
any following
global/generic
load/load
atomic/store/store
atomic/atomicrmw.
- Ensures that
following loads
will not see stale
global data. This
satisfies the
requirements of
acquire.
**Sequential Consistent Atomic**
-----------------------------------------------------------------------------------
load atomic seq_cst - singlethread - global *Same as corresponding
- wavefront - local load atomic acquire,
- generic except must generated
all instructions even
for OpenCL.*
load atomic seq_cst - workgroup - global 1. s_waitcnt lgkmcnt(0)
- generic
- Must
happen after
preceding
global/generic load
atomic/store
atomic/atomicrmw
with memory
ordering of seq_cst
and with equal or
wider sync scope.
(Note that seq_cst
fences have their
own s_waitcnt
lgkmcnt(0) and so do
not need to be
considered.)
- Ensures any
preceding
sequential
consistent local
memory instructions
have completed
before executing
this sequentially
consistent
instruction. This
prevents reordering
a seq_cst store
followed by a
seq_cst load. (Note
that seq_cst is
stronger than
acquire/release as
the reordering of
load acquire
followed by a store
release is
prevented by the
waitcnt of
the release, but
there is nothing
preventing a store
release followed by
load acquire from
competing out of
order.)
2. *Following
instructions same as
corresponding load
atomic acquire,
except must generated
all instructions even
for OpenCL.*
load atomic seq_cst - workgroup - local *Same as corresponding
load atomic acquire,
except must generated
all instructions even
for OpenCL.*
load atomic seq_cst - agent - global 1. s_waitcnt lgkmcnt(0) &
- system - generic vmcnt(0)
- Could be split into
separate s_waitcnt
vmcnt(0)
and s_waitcnt
lgkmcnt(0) to allow
them to be
independently moved
according to the
following rules.
- waitcnt lgkmcnt(0)
must happen after
preceding
global/generic load
atomic/store
atomic/atomicrmw
with memory
ordering of seq_cst
and with equal or
wider sync scope.
(Note that seq_cst
fences have their
own s_waitcnt
lgkmcnt(0) and so do
not need to be
considered.)
- waitcnt vmcnt(0)
must happen after
preceding
global/generic load
atomic/store
atomic/atomicrmw
with memory
ordering of seq_cst
and with equal or
wider sync scope.
(Note that seq_cst
fences have their
own s_waitcnt
vmcnt(0) and so do
not need to be
considered.)
- Ensures any
preceding
sequential
consistent global
memory instructions
have completed
before executing
this sequentially
consistent
instruction. This
prevents reordering
a seq_cst store
followed by a
seq_cst load. (Note
that seq_cst is
stronger than
acquire/release as
the reordering of
load acquire
followed by a store
release is
prevented by the
waitcnt of
the release, but
there is nothing
preventing a store
release followed by
load acquire from
competing out of
order.)
2. *Following
instructions same as
corresponding load
atomic acquire,
except must generated
all instructions even
for OpenCL.*
store atomic seq_cst - singlethread - global *Same as corresponding
- wavefront - local store atomic release,
- workgroup - generic except must generated
all instructions even
for OpenCL.*
store atomic seq_cst - agent - global *Same as corresponding
- system - generic store atomic release,
except must generated
all instructions even
for OpenCL.*
atomicrmw seq_cst - singlethread - global *Same as corresponding
- wavefront - local atomicrmw acq_rel,
- workgroup - generic except must generated
all instructions even
for OpenCL.*
atomicrmw seq_cst - agent - global *Same as corresponding
- system - generic atomicrmw acq_rel,
except must generated
all instructions even
for OpenCL.*
fence seq_cst - singlethread *none* *Same as corresponding
- wavefront fence acq_rel,
- workgroup except must generated
- agent all instructions even
- system for OpenCL.*
============ ============ ============== ========== ===============================
The memory order also adds the single thread optimization constrains defined in
table
:ref:`amdgpu-amdhsa-memory-model-single-thread-optimization-constraints-gfx6-gfx9-table`.
.. table:: AMDHSA Memory Model Single Thread Optimization Constraints GFX6-GFX9
:name: amdgpu-amdhsa-memory-model-single-thread-optimization-constraints-gfx6-gfx9-table
============ ==============================================================
LLVM Memory Optimization Constraints
Ordering
============ ==============================================================
unordered *none*
monotonic *none*
acquire - If a load atomic/atomicrmw then no following load/load
atomic/store/ store atomic/atomicrmw/fence instruction can
be moved before the acquire.
- If a fence then same as load atomic, plus no preceding
associated fence-paired-atomic can be moved after the fence.
release - If a store atomic/atomicrmw then no preceding load/load
atomic/store/ store atomic/atomicrmw/fence instruction can
be moved after the release.
- If a fence then same as store atomic, plus no following
associated fence-paired-atomic can be moved before the
fence.
acq_rel Same constraints as both acquire and release.
seq_cst - If a load atomic then same constraints as acquire, plus no
preceding sequentially consistent load atomic/store
atomic/atomicrmw/fence instruction can be moved after the
seq_cst.
- If a store atomic then the same constraints as release, plus
no following sequentially consistent load atomic/store
atomic/atomicrmw/fence instruction can be moved before the
seq_cst.
- If an atomicrmw/fence then same constraints as acq_rel.
============ ==============================================================
Trap Handler ABI
~~~~~~~~~~~~~~~~
For code objects generated by AMDGPU backend for HSA [HSA]_ compatible runtimes
(such as ROCm [AMD-ROCm]_), the runtime installs a trap handler that supports
the ``s_trap`` instruction with the following usage:
.. table:: AMDGPU Trap Handler for AMDHSA OS
:name: amdgpu-trap-handler-for-amdhsa-os-table
=================== =============== =============== =======================
Usage Code Sequence Trap Handler Description
Inputs
=================== =============== =============== =======================
reserved ``s_trap 0x00`` Reserved by hardware.
``debugtrap(arg)`` ``s_trap 0x01`` ``SGPR0-1``: Reserved for HSA
``queue_ptr`` ``debugtrap``
``VGPR0``: intrinsic (not
``arg`` implemented).
``llvm.trap`` ``s_trap 0x02`` ``SGPR0-1``: Causes dispatch to be
``queue_ptr`` terminated and its
associated queue put
into the error state.
``llvm.debugtrap`` ``s_trap 0x03`` ``SGPR0-1``: If debugger not
``queue_ptr`` installed handled
same as ``llvm.trap``.
debugger breakpoint ``s_trap 0x07`` Reserved for debugger
breakpoints.
debugger ``s_trap 0x08`` Reserved for debugger.
debugger ``s_trap 0xfe`` Reserved for debugger.
debugger ``s_trap 0xff`` Reserved for debugger.
=================== =============== =============== =======================
Unspecified OS
--------------
This section provides code conventions used when the target triple OS is
empty (see :ref:`amdgpu-target-triples`).
Trap Handler ABI
~~~~~~~~~~~~~~~~
For code objects generated by AMDGPU backend for non-amdhsa OS, the runtime does
not install a trap handler. The ``llvm.trap`` and ``llvm.debugtrap``
instructions are handled as follows:
.. table:: AMDGPU Trap Handler for Non-AMDHSA OS
:name: amdgpu-trap-handler-for-non-amdhsa-os-table
=============== =============== ===========================================
Usage Code Sequence Description
=============== =============== ===========================================
llvm.trap s_endpgm Causes wavefront to be terminated.
llvm.debugtrap *none* Compiler warning given that there is no
trap handler installed.
=============== =============== ===========================================
Source Languages
================
.. _amdgpu-opencl:
OpenCL
------
When generating code for the OpenCL language the target triple environment
should be ``opencl`` or ``amdgizcl`` (see :ref:`amdgpu-target-triples`).
When the language is OpenCL the following differences occur:
1. The OpenCL memory model is used (see :ref:`amdgpu-amdhsa-memory-model`).
2. The AMDGPU backend adds additional arguments to the kernel.
3. Additional metadata is generated
(:ref:`amdgpu-amdhsa-hsa-code-object-metadata`).
.. TODO
Specify what affect this has. Hidden arguments added. Additional metadata
generated.
.. _amdgpu-hcc:
HCC
---
When generating code for the OpenCL language the target triple environment
should be ``hcc`` (see :ref:`amdgpu-target-triples`).
When the language is OpenCL the following differences occur:
1. The HSA memory model is used (see :ref:`amdgpu-amdhsa-memory-model`).
.. TODO
Specify what affect this has.
Assembler
---------
AMDGPU backend has LLVM-MC based assembler which is currently in development.
It supports AMDGCN GFX6-GFX8.
This section describes general syntax for instructions and operands. For more
information about instructions, their semantics and supported combinations of
operands, refer to one of instruction set architecture manuals
[AMD-GCN-GFX6]_, [AMD-GCN-GFX7]_, [AMD-GCN-GFX8]_ and [AMD-GCN-GFX9]_.
An instruction has the following syntax (register operands are normally
comma-separated while extra operands are space-separated):
*<opcode> <register_operand0>, ... <extra_operand0> ...*
Operands
~~~~~~~~
The following syntax for register operands is supported:
* SGPR registers: s0, ... or s[0], ...
* VGPR registers: v0, ... or v[0], ...
* TTMP registers: ttmp0, ... or ttmp[0], ...
* Special registers: exec (exec_lo, exec_hi), vcc (vcc_lo, vcc_hi), flat_scratch (flat_scratch_lo, flat_scratch_hi)
* Special trap registers: tba (tba_lo, tba_hi), tma (tma_lo, tma_hi)
* Register pairs, quads, etc: s[2:3], v[10:11], ttmp[5:6], s[4:7], v[12:15], ttmp[4:7], s[8:15], ...
* Register lists: [s0, s1], [ttmp0, ttmp1, ttmp2, ttmp3]
* Register index expressions: v[2*2], s[1-1:2-1]
* 'off' indicates that an operand is not enabled
The following extra operands are supported:
* offset, offset0, offset1
* idxen, offen bits
* glc, slc, tfe bits
* waitcnt: integer or combination of counter values
* VOP3 modifiers:
- abs (\| \|), neg (\-)
* DPP modifiers:
- row_shl, row_shr, row_ror, row_rol
- row_mirror, row_half_mirror, row_bcast
- wave_shl, wave_shr, wave_ror, wave_rol, quad_perm
- row_mask, bank_mask, bound_ctrl
* SDWA modifiers:
- dst_sel, src0_sel, src1_sel (BYTE_N, WORD_M, DWORD)
- dst_unused (UNUSED_PAD, UNUSED_SEXT, UNUSED_PRESERVE)
- abs, neg, sext
Instruction Examples
~~~~~~~~~~~~~~~~~~~~
DS
~~
.. code-block:: nasm
ds_add_u32 v2, v4 offset:16
ds_write_src2_b64 v2 offset0:4 offset1:8
ds_cmpst_f32 v2, v4, v6
ds_min_rtn_f64 v[8:9], v2, v[4:5]
For full list of supported instructions, refer to "LDS/GDS instructions" in ISA Manual.
FLAT
++++
.. code-block:: nasm
flat_load_dword v1, v[3:4]
flat_store_dwordx3 v[3:4], v[5:7]
flat_atomic_swap v1, v[3:4], v5 glc
flat_atomic_cmpswap v1, v[3:4], v[5:6] glc slc
flat_atomic_fmax_x2 v[1:2], v[3:4], v[5:6] glc
For full list of supported instructions, refer to "FLAT instructions" in ISA Manual.
MUBUF
+++++
.. code-block:: nasm
buffer_load_dword v1, off, s[4:7], s1
buffer_store_dwordx4 v[1:4], v2, ttmp[4:7], s1 offen offset:4 glc tfe
buffer_store_format_xy v[1:2], off, s[4:7], s1
buffer_wbinvl1
buffer_atomic_inc v1, v2, s[8:11], s4 idxen offset:4 slc
For full list of supported instructions, refer to "MUBUF Instructions" in ISA Manual.
SMRD/SMEM
+++++++++
.. code-block:: nasm
s_load_dword s1, s[2:3], 0xfc
s_load_dwordx8 s[8:15], s[2:3], s4
s_load_dwordx16 s[88:103], s[2:3], s4
s_dcache_inv_vol
s_memtime s[4:5]
For full list of supported instructions, refer to "Scalar Memory Operations" in ISA Manual.
SOP1
++++
.. code-block:: nasm
s_mov_b32 s1, s2
s_mov_b64 s[0:1], 0x80000000
s_cmov_b32 s1, 200
s_wqm_b64 s[2:3], s[4:5]
s_bcnt0_i32_b64 s1, s[2:3]
s_swappc_b64 s[2:3], s[4:5]
s_cbranch_join s[4:5]
For full list of supported instructions, refer to "SOP1 Instructions" in ISA Manual.
SOP2
++++
.. code-block:: nasm
s_add_u32 s1, s2, s3
s_and_b64 s[2:3], s[4:5], s[6:7]
s_cselect_b32 s1, s2, s3
s_andn2_b32 s2, s4, s6
s_lshr_b64 s[2:3], s[4:5], s6
s_ashr_i32 s2, s4, s6
s_bfm_b64 s[2:3], s4, s6
s_bfe_i64 s[2:3], s[4:5], s6
s_cbranch_g_fork s[4:5], s[6:7]
For full list of supported instructions, refer to "SOP2 Instructions" in ISA Manual.
SOPC
++++
.. code-block:: nasm
s_cmp_eq_i32 s1, s2
s_bitcmp1_b32 s1, s2
s_bitcmp0_b64 s[2:3], s4
s_setvskip s3, s5
For full list of supported instructions, refer to "SOPC Instructions" in ISA Manual.
SOPP
++++
.. code-block:: nasm
s_barrier
s_nop 2
s_endpgm
s_waitcnt 0 ; Wait for all counters to be 0
s_waitcnt vmcnt(0) & expcnt(0) & lgkmcnt(0) ; Equivalent to above
s_waitcnt vmcnt(1) ; Wait for vmcnt counter to be 1.
s_sethalt 9
s_sleep 10
s_sendmsg 0x1
s_sendmsg sendmsg(MSG_INTERRUPT)
s_trap 1
For full list of supported instructions, refer to "SOPP Instructions" in ISA Manual.
Unless otherwise mentioned, little verification is performed on the operands
of SOPP Instructions, so it is up to the programmer to be familiar with the
range or acceptable values.
VALU
++++
For vector ALU instruction opcodes (VOP1, VOP2, VOP3, VOPC, VOP_DPP, VOP_SDWA),
the assembler will automatically use optimal encoding based on its operands.
To force specific encoding, one can add a suffix to the opcode of the instruction:
* _e32 for 32-bit VOP1/VOP2/VOPC
* _e64 for 64-bit VOP3
* _dpp for VOP_DPP
* _sdwa for VOP_SDWA
VOP1/VOP2/VOP3/VOPC examples:
.. code-block:: nasm
v_mov_b32 v1, v2
v_mov_b32_e32 v1, v2
v_nop
v_cvt_f64_i32_e32 v[1:2], v2
v_floor_f32_e32 v1, v2
v_bfrev_b32_e32 v1, v2
v_add_f32_e32 v1, v2, v3
v_mul_i32_i24_e64 v1, v2, 3
v_mul_i32_i24_e32 v1, -3, v3
v_mul_i32_i24_e32 v1, -100, v3
v_addc_u32 v1, s[0:1], v2, v3, s[2:3]
v_max_f16_e32 v1, v2, v3
VOP_DPP examples:
.. code-block:: nasm
v_mov_b32 v0, v0 quad_perm:[0,2,1,1]
v_sin_f32 v0, v0 row_shl:1 row_mask:0xa bank_mask:0x1 bound_ctrl:0
v_mov_b32 v0, v0 wave_shl:1
v_mov_b32 v0, v0 row_mirror
v_mov_b32 v0, v0 row_bcast:31
v_mov_b32 v0, v0 quad_perm:[1,3,0,1] row_mask:0xa bank_mask:0x1 bound_ctrl:0
v_add_f32 v0, v0, |v0| row_shl:1 row_mask:0xa bank_mask:0x1 bound_ctrl:0
v_max_f16 v1, v2, v3 row_shl:1 row_mask:0xa bank_mask:0x1 bound_ctrl:0
VOP_SDWA examples:
.. code-block:: nasm
v_mov_b32 v1, v2 dst_sel:BYTE_0 dst_unused:UNUSED_PRESERVE src0_sel:DWORD
v_min_u32 v200, v200, v1 dst_sel:WORD_1 dst_unused:UNUSED_PAD src0_sel:BYTE_1 src1_sel:DWORD
v_sin_f32 v0, v0 dst_unused:UNUSED_PAD src0_sel:WORD_1
v_fract_f32 v0, |v0| dst_sel:DWORD dst_unused:UNUSED_PAD src0_sel:WORD_1
v_cmpx_le_u32 vcc, v1, v2 src0_sel:BYTE_2 src1_sel:WORD_0
For full list of supported instructions, refer to "Vector ALU instructions".
HSA Code Object Directives
~~~~~~~~~~~~~~~~~~~~~~~~~~
AMDGPU ABI defines auxiliary data in output code object. In assembly source,
one can specify them with assembler directives.
.hsa_code_object_version major, minor
+++++++++++++++++++++++++++++++++++++
*major* and *minor* are integers that specify the version of the HSA code
object that will be generated by the assembler.
.hsa_code_object_isa [major, minor, stepping, vendor, arch]
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
*major*, *minor*, and *stepping* are all integers that describe the instruction
set architecture (ISA) version of the assembly program.
*vendor* and *arch* are quoted strings. *vendor* should always be equal to
"AMD" and *arch* should always be equal to "AMDGPU".
By default, the assembler will derive the ISA version, *vendor*, and *arch*
from the value of the -mcpu option that is passed to the assembler.
.amdgpu_hsa_kernel (name)
+++++++++++++++++++++++++
This directives specifies that the symbol with given name is a kernel entry point
(label) and the object should contain corresponding symbol of type STT_AMDGPU_HSA_KERNEL.
.amd_kernel_code_t
++++++++++++++++++
This directive marks the beginning of a list of key / value pairs that are used
to specify the amd_kernel_code_t object that will be emitted by the assembler.
The list must be terminated by the *.end_amd_kernel_code_t* directive. For
any amd_kernel_code_t values that are unspecified a default value will be
used. The default value for all keys is 0, with the following exceptions:
- *kernel_code_version_major* defaults to 1.
- *machine_kind* defaults to 1.
- *machine_version_major*, *machine_version_minor*, and
*machine_version_stepping* are derived from the value of the -mcpu option
that is passed to the assembler.
- *kernel_code_entry_byte_offset* defaults to 256.
- *wavefront_size* defaults to 6.
- *kernarg_segment_alignment*, *group_segment_alignment*, and
*private_segment_alignment* default to 4. Note that alignments are specified
as a power of two, so a value of **n** means an alignment of 2^ **n**.
The *.amd_kernel_code_t* directive must be placed immediately after the
function label and before any instructions.
For a full list of amd_kernel_code_t keys, refer to AMDGPU ABI document,
comments in lib/Target/AMDGPU/AmdKernelCodeT.h and test/CodeGen/AMDGPU/hsa.s.
Here is an example of a minimal amd_kernel_code_t specification:
.. code-block:: none
.hsa_code_object_version 1,0
.hsa_code_object_isa
.hsatext
.globl hello_world
.p2align 8
.amdgpu_hsa_kernel hello_world
hello_world:
.amd_kernel_code_t
enable_sgpr_kernarg_segment_ptr = 1
is_ptr64 = 1
compute_pgm_rsrc1_vgprs = 0
compute_pgm_rsrc1_sgprs = 0
compute_pgm_rsrc2_user_sgpr = 2
kernarg_segment_byte_size = 8
wavefront_sgpr_count = 2
workitem_vgpr_count = 3
.end_amd_kernel_code_t
s_load_dwordx2 s[0:1], s[0:1] 0x0
v_mov_b32 v0, 3.14159
s_waitcnt lgkmcnt(0)
v_mov_b32 v1, s0
v_mov_b32 v2, s1
flat_store_dword v[1:2], v0
s_endpgm
.Lfunc_end0:
.size hello_world, .Lfunc_end0-hello_world
Additional Documentation
========================
.. [AMD-RADEON-HD-2000-3000] `AMD R6xx shader ISA <http://developer.amd.com/wordpress/media/2012/10/R600_Instruction_Set_Architecture.pdf>`__
.. [AMD-RADEON-HD-4000] `AMD R7xx shader ISA <http://developer.amd.com/wordpress/media/2012/10/R700-Family_Instruction_Set_Architecture.pdf>`__
.. [AMD-RADEON-HD-5000] `AMD Evergreen shader ISA <http://developer.amd.com/wordpress/media/2012/10/AMD_Evergreen-Family_Instruction_Set_Architecture.pdf>`__
.. [AMD-RADEON-HD-6000] `AMD Cayman/Trinity shader ISA <http://developer.amd.com/wordpress/media/2012/10/AMD_HD_6900_Series_Instruction_Set_Architecture.pdf>`__
.. [AMD-GCN-GFX6] `AMD Southern Islands Series ISA <http://developer.amd.com/wordpress/media/2012/12/AMD_Southern_Islands_Instruction_Set_Architecture.pdf>`__
.. [AMD-GCN-GFX7] `AMD Sea Islands Series ISA <http://developer.amd.com/wordpress/media/2013/07/AMD_Sea_Islands_Instruction_Set_Architecture.pdf>`_
.. [AMD-GCN-GFX8] `AMD GCN3 Instruction Set Architecture <http://amd-dev.wpengine.netdna-cdn.com/wordpress/media/2013/12/AMD_GCN3_Instruction_Set_Architecture_rev1.1.pdf>`__
.. [AMD-GCN-GFX9] `AMD "Vega" Instruction Set Architecture <http://developer.amd.com/wordpress/media/2013/12/Vega_Shader_ISA_28July2017.pdf>`__
.. [AMD-OpenCL_Programming-Guide] `AMD Accelerated Parallel Processing OpenCL Programming Guide <http://developer.amd.com/download/AMD_Accelerated_Parallel_Processing_OpenCL_Programming_Guide.pdf>`_
.. [AMD-APP-SDK] `AMD Accelerated Parallel Processing APP SDK Documentation <http://developer.amd.com/tools/heterogeneous-computing/amd-accelerated-parallel-processing-app-sdk/documentation/>`__
.. [AMD-ROCm] `ROCm: Open Platform for Development, Discovery and Education Around GPU Computing <http://gpuopen.com/compute-product/rocm/>`__
.. [AMD-ROCm-github] `ROCm github <http://github.com/RadeonOpenCompute>`__
.. [HSA] `Heterogeneous System Architecture (HSA) Foundation <http://www.hsafoundation.com/>`__
.. [ELF] `Executable and Linkable Format (ELF) <http://www.sco.com/developers/gabi/>`__
.. [DWARF] `DWARF Debugging Information Format <http://dwarfstd.org/>`__
.. [YAML] `YAML Ain't Markup Language (YAML™) Version 1.2 <http://www.yaml.org/spec/1.2/spec.html>`__
.. [OpenCL] `The OpenCL Specification Version 2.0 <http://www.khronos.org/registry/cl/specs/opencl-2.0.pdf>`__
.. [HRF] `Heterogeneous-race-free Memory Models <http://benedictgaster.org/wp-content/uploads/2014/01/asplos269-FINAL.pdf>`__
.. [AMD-AMDGPU-Compute-Application-Binary-Interface] `AMDGPU Compute Application Binary Interface <https://github.com/RadeonOpenCompute/ROCm-ComputeABI-Doc/blob/master/AMDGPU-ABI.md>`__
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