mirror of
https://github.com/RPCSX/llvm.git
synced 2024-12-05 02:16:46 +00:00
0aeea88439
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@247005 91177308-0d34-0410-b5e6-96231b3b80d8
496 lines
14 KiB
ReStructuredText
496 lines
14 KiB
ReStructuredText
========================================
|
|
Machine IR (MIR) Format Reference Manual
|
|
========================================
|
|
|
|
.. contents::
|
|
:local:
|
|
|
|
.. warning::
|
|
This is a work in progress.
|
|
|
|
Introduction
|
|
============
|
|
|
|
This document is a reference manual for the Machine IR (MIR) serialization
|
|
format. MIR is a human readable serialization format that is used to represent
|
|
LLVM's :ref:`machine specific intermediate representation
|
|
<machine code representation>`.
|
|
|
|
The MIR serialization format is designed to be used for testing the code
|
|
generation passes in LLVM.
|
|
|
|
Overview
|
|
========
|
|
|
|
The MIR serialization format uses a YAML container. YAML is a standard
|
|
data serialization language, and the full YAML language spec can be read at
|
|
`yaml.org
|
|
<http://www.yaml.org/spec/1.2/spec.html#Introduction>`_.
|
|
|
|
A MIR file is split up into a series of `YAML documents`_. The first document
|
|
can contain an optional embedded LLVM IR module, and the rest of the documents
|
|
contain the serialized machine functions.
|
|
|
|
.. _YAML documents: http://www.yaml.org/spec/1.2/spec.html#id2800132
|
|
|
|
MIR Testing Guide
|
|
=================
|
|
|
|
You can use the MIR format for testing in two different ways:
|
|
|
|
- You can write MIR tests that invoke a single code generation pass using the
|
|
``run-pass`` option in llc.
|
|
|
|
- You can use llc's ``stop-after`` option with existing or new LLVM assembly
|
|
tests and check the MIR output of a specific code generation pass.
|
|
|
|
Testing Individual Code Generation Passes
|
|
-----------------------------------------
|
|
|
|
The ``run-pass`` option in llc allows you to create MIR tests that invoke
|
|
just a single code generation pass. When this option is used, llc will parse
|
|
an input MIR file, run the specified code generation pass, and print the
|
|
resulting MIR to the standard output stream.
|
|
|
|
You can generate an input MIR file for the test by using the ``stop-after``
|
|
option in llc. For example, if you would like to write a test for the
|
|
post register allocation pseudo instruction expansion pass, you can specify
|
|
the machine copy propagation pass in the ``stop-after`` option, as it runs
|
|
just before the pass that we are trying to test:
|
|
|
|
``llc -stop-after machine-cp bug-trigger.ll > test.mir``
|
|
|
|
After generating the input MIR file, you'll have to add a run line that uses
|
|
the ``-run-pass`` option to it. In order to test the post register allocation
|
|
pseudo instruction expansion pass on X86-64, a run line like the one shown
|
|
below can be used:
|
|
|
|
``# RUN: llc -run-pass postrapseudos -march=x86-64 %s -o /dev/null | FileCheck %s``
|
|
|
|
The MIR files are target dependent, so they have to be placed in the target
|
|
specific test directories. They also need to specify a target triple or a
|
|
target architecture either in the run line or in the embedded LLVM IR module.
|
|
|
|
Limitations
|
|
-----------
|
|
|
|
Currently the MIR format has several limitations in terms of which state it
|
|
can serialize:
|
|
|
|
- The target-specific state in the target-specific ``MachineFunctionInfo``
|
|
subclasses isn't serialized at the moment.
|
|
|
|
- The target-specific ``MachineConstantPoolValue`` subclasses (in the ARM and
|
|
SystemZ backends) aren't serialized at the moment.
|
|
|
|
- The ``MCSymbol`` machine operands are only printed, they can't be parsed.
|
|
|
|
- A lot of the state in ``MachineModuleInfo`` isn't serialized - only the CFI
|
|
instructions and the variable debug information from MMI is serialized right
|
|
now.
|
|
|
|
These limitations impose restrictions on what you can test with the MIR format.
|
|
For now, tests that would like to test some behaviour that depends on the state
|
|
of certain ``MCSymbol`` operands or the exception handling state in MMI, can't
|
|
use the MIR format. As well as that, tests that test some behaviour that
|
|
depends on the state of the target specific ``MachineFunctionInfo`` or
|
|
``MachineConstantPoolValue`` subclasses can't use the MIR format at the moment.
|
|
|
|
High Level Structure
|
|
====================
|
|
|
|
.. _embedded-module:
|
|
|
|
Embedded Module
|
|
---------------
|
|
|
|
When the first YAML document contains a `YAML block literal string`_, the MIR
|
|
parser will treat this string as an LLVM assembly language string that
|
|
represents an embedded LLVM IR module.
|
|
Here is an example of a YAML document that contains an LLVM module:
|
|
|
|
.. code-block:: llvm
|
|
|
|
--- |
|
|
define i32 @inc(i32* %x) {
|
|
entry:
|
|
%0 = load i32, i32* %x
|
|
%1 = add i32 %0, 1
|
|
store i32 %1, i32* %x
|
|
ret i32 %1
|
|
}
|
|
...
|
|
|
|
.. _YAML block literal string: http://www.yaml.org/spec/1.2/spec.html#id2795688
|
|
|
|
Machine Functions
|
|
-----------------
|
|
|
|
The remaining YAML documents contain the machine functions. This is an example
|
|
of such YAML document:
|
|
|
|
.. code-block:: llvm
|
|
|
|
---
|
|
name: inc
|
|
tracksRegLiveness: true
|
|
liveins:
|
|
- { reg: '%rdi' }
|
|
body: |
|
|
bb.0.entry:
|
|
liveins: %rdi
|
|
|
|
%eax = MOV32rm %rdi, 1, _, 0, _
|
|
%eax = INC32r killed %eax, implicit-def dead %eflags
|
|
MOV32mr killed %rdi, 1, _, 0, _, %eax
|
|
RETQ %eax
|
|
...
|
|
|
|
The document above consists of attributes that represent the various
|
|
properties and data structures in a machine function.
|
|
|
|
The attribute ``name`` is required, and its value should be identical to the
|
|
name of a function that this machine function is based on.
|
|
|
|
The attribute ``body`` is a `YAML block literal string`_. Its value represents
|
|
the function's machine basic blocks and their machine instructions.
|
|
|
|
Machine Instructions Format Reference
|
|
=====================================
|
|
|
|
The machine basic blocks and their instructions are represented using a custom,
|
|
human readable serialization language. This language is used in the
|
|
`YAML block literal string`_ that corresponds to the machine function's body.
|
|
|
|
A source string that uses this language contains a list of machine basic
|
|
blocks, which are described in the section below.
|
|
|
|
Machine Basic Blocks
|
|
--------------------
|
|
|
|
A machine basic block is defined in a single block definition source construct
|
|
that contains the block's ID.
|
|
The example below defines two blocks that have an ID of zero and one:
|
|
|
|
.. code-block:: llvm
|
|
|
|
bb.0:
|
|
<instructions>
|
|
bb.1:
|
|
<instructions>
|
|
|
|
A machine basic block can also have a name. It should be specified after the ID
|
|
in the block's definition:
|
|
|
|
.. code-block:: llvm
|
|
|
|
bb.0.entry: ; This block's name is "entry"
|
|
<instructions>
|
|
|
|
The block's name should be identical to the name of the IR block that this
|
|
machine block is based on.
|
|
|
|
Block References
|
|
^^^^^^^^^^^^^^^^
|
|
|
|
The machine basic blocks are identified by their ID numbers. Individual
|
|
blocks are referenced using the following syntax:
|
|
|
|
.. code-block:: llvm
|
|
|
|
%bb.<id>[.<name>]
|
|
|
|
Examples:
|
|
|
|
.. code-block:: llvm
|
|
|
|
%bb.0
|
|
%bb.1.then
|
|
|
|
Successors
|
|
^^^^^^^^^^
|
|
|
|
The machine basic block's successors have to be specified before any of the
|
|
instructions:
|
|
|
|
.. code-block:: llvm
|
|
|
|
bb.0.entry:
|
|
successors: %bb.1.then, %bb.2.else
|
|
<instructions>
|
|
bb.1.then:
|
|
<instructions>
|
|
bb.2.else:
|
|
<instructions>
|
|
|
|
The branch weights can be specified in brackets after the successor blocks.
|
|
The example below defines a block that has two successors with branch weights
|
|
of 32 and 16:
|
|
|
|
.. code-block:: llvm
|
|
|
|
bb.0.entry:
|
|
successors: %bb.1.then(32), %bb.2.else(16)
|
|
|
|
.. _bb-liveins:
|
|
|
|
Live In Registers
|
|
^^^^^^^^^^^^^^^^^
|
|
|
|
The machine basic block's live in registers have to be specified before any of
|
|
the instructions:
|
|
|
|
.. code-block:: llvm
|
|
|
|
bb.0.entry:
|
|
liveins: %edi, %esi
|
|
|
|
The list of live in registers and successors can be empty. The language also
|
|
allows multiple live in register and successor lists - they are combined into
|
|
one list by the parser.
|
|
|
|
Miscellaneous Attributes
|
|
^^^^^^^^^^^^^^^^^^^^^^^^
|
|
|
|
The attributes ``IsAddressTaken``, ``IsLandingPad`` and ``Alignment`` can be
|
|
specified in brackets after the block's definition:
|
|
|
|
.. code-block:: llvm
|
|
|
|
bb.0.entry (address-taken):
|
|
<instructions>
|
|
bb.2.else (align 4):
|
|
<instructions>
|
|
bb.3(landing-pad, align 4):
|
|
<instructions>
|
|
|
|
.. TODO: Describe the way the reference to an unnamed LLVM IR block can be
|
|
preserved.
|
|
|
|
Machine Instructions
|
|
--------------------
|
|
|
|
A machine instruction is composed of a name,
|
|
:ref:`machine operands <machine-operands>`,
|
|
:ref:`instruction flags <instruction-flags>`, and machine memory operands.
|
|
|
|
The instruction's name is usually specified before the operands. The example
|
|
below shows an instance of the X86 ``RETQ`` instruction with a single machine
|
|
operand:
|
|
|
|
.. code-block:: llvm
|
|
|
|
RETQ %eax
|
|
|
|
However, if the machine instruction has one or more explicitly defined register
|
|
operands, the instruction's name has to be specified after them. The example
|
|
below shows an instance of the AArch64 ``LDPXpost`` instruction with three
|
|
defined register operands:
|
|
|
|
.. code-block:: llvm
|
|
|
|
%sp, %fp, %lr = LDPXpost %sp, 2
|
|
|
|
The instruction names are serialized using the exact definitions from the
|
|
target's ``*InstrInfo.td`` files, and they are case sensitive. This means that
|
|
similar instruction names like ``TSTri`` and ``tSTRi`` represent different
|
|
machine instructions.
|
|
|
|
.. _instruction-flags:
|
|
|
|
Instruction Flags
|
|
^^^^^^^^^^^^^^^^^
|
|
|
|
The flag ``frame-setup`` can be specified before the instruction's name:
|
|
|
|
.. code-block:: llvm
|
|
|
|
%fp = frame-setup ADDXri %sp, 0, 0
|
|
|
|
.. _registers:
|
|
|
|
Registers
|
|
---------
|
|
|
|
Registers are one of the key primitives in the machine instructions
|
|
serialization language. They are primarly used in the
|
|
:ref:`register machine operands <register-operands>`,
|
|
but they can also be used in a number of other places, like the
|
|
:ref:`basic block's live in list <bb-liveins>`.
|
|
|
|
The physical registers are identified by their name. They use the following
|
|
syntax:
|
|
|
|
.. code-block:: llvm
|
|
|
|
%<name>
|
|
|
|
The example below shows three X86 physical registers:
|
|
|
|
.. code-block:: llvm
|
|
|
|
%eax
|
|
%r15
|
|
%eflags
|
|
|
|
The virtual registers are identified by their ID number. They use the following
|
|
syntax:
|
|
|
|
.. code-block:: llvm
|
|
|
|
%<id>
|
|
|
|
Example:
|
|
|
|
.. code-block:: llvm
|
|
|
|
%0
|
|
|
|
The null registers are represented using an underscore ('``_``'). They can also be
|
|
represented using a '``%noreg``' named register, although the former syntax
|
|
is preferred.
|
|
|
|
.. _machine-operands:
|
|
|
|
Machine Operands
|
|
----------------
|
|
|
|
There are seventeen different kinds of machine operands, and all of them, except
|
|
the ``MCSymbol`` operand, can be serialized. The ``MCSymbol`` operands are
|
|
just printed out - they can't be parsed back yet.
|
|
|
|
Immediate Operands
|
|
^^^^^^^^^^^^^^^^^^
|
|
|
|
The immediate machine operands are untyped, 64-bit signed integers. The
|
|
example below shows an instance of the X86 ``MOV32ri`` instruction that has an
|
|
immediate machine operand ``-42``:
|
|
|
|
.. code-block:: llvm
|
|
|
|
%eax = MOV32ri -42
|
|
|
|
.. TODO: Describe the CIMM (Rare) and FPIMM immediate operands.
|
|
|
|
.. _register-operands:
|
|
|
|
Register Operands
|
|
^^^^^^^^^^^^^^^^^
|
|
|
|
The :ref:`register <registers>` primitive is used to represent the register
|
|
machine operands. The register operands can also have optional
|
|
:ref:`register flags <register-flags>`,
|
|
:ref:`a subregister index <subregister-indices>`,
|
|
and a reference to the tied register operand.
|
|
The full syntax of a register operand is shown below:
|
|
|
|
.. code-block:: llvm
|
|
|
|
[<flags>] <register> [ :<subregister-idx-name> ] [ (tied-def <tied-op>) ]
|
|
|
|
This example shows an instance of the X86 ``XOR32rr`` instruction that has
|
|
5 register operands with different register flags:
|
|
|
|
.. code-block:: llvm
|
|
|
|
dead %eax = XOR32rr undef %eax, undef %eax, implicit-def dead %eflags, implicit-def %al
|
|
|
|
.. _register-flags:
|
|
|
|
Register Flags
|
|
~~~~~~~~~~~~~~
|
|
|
|
The table below shows all of the possible register flags along with the
|
|
corresponding internal ``llvm::RegState`` representation:
|
|
|
|
.. list-table::
|
|
:header-rows: 1
|
|
|
|
* - Flag
|
|
- Internal Value
|
|
|
|
* - ``implicit``
|
|
- ``RegState::Implicit``
|
|
|
|
* - ``implicit-def``
|
|
- ``RegState::ImplicitDefine``
|
|
|
|
* - ``def``
|
|
- ``RegState::Define``
|
|
|
|
* - ``dead``
|
|
- ``RegState::Dead``
|
|
|
|
* - ``killed``
|
|
- ``RegState::Kill``
|
|
|
|
* - ``undef``
|
|
- ``RegState::Undef``
|
|
|
|
* - ``internal``
|
|
- ``RegState::InternalRead``
|
|
|
|
* - ``early-clobber``
|
|
- ``RegState::EarlyClobber``
|
|
|
|
* - ``debug-use``
|
|
- ``RegState::Debug``
|
|
|
|
.. _subregister-indices:
|
|
|
|
Subregister Indices
|
|
~~~~~~~~~~~~~~~~~~~
|
|
|
|
The register machine operands can reference a portion of a register by using
|
|
the subregister indices. The example below shows an instance of the ``COPY``
|
|
pseudo instruction that uses the X86 ``sub_8bit`` subregister index to copy 8
|
|
lower bits from the 32-bit virtual register 0 to the 8-bit virtual register 1:
|
|
|
|
.. code-block:: llvm
|
|
|
|
%1 = COPY %0:sub_8bit
|
|
|
|
The names of the subregister indices are target specific, and are typically
|
|
defined in the target's ``*RegisterInfo.td`` file.
|
|
|
|
Global Value Operands
|
|
^^^^^^^^^^^^^^^^^^^^^
|
|
|
|
The global value machine operands reference the global values from the
|
|
:ref:`embedded LLVM IR module <embedded-module>`.
|
|
The example below shows an instance of the X86 ``MOV64rm`` instruction that has
|
|
a global value operand named ``G``:
|
|
|
|
.. code-block:: llvm
|
|
|
|
%rax = MOV64rm %rip, 1, _, @G, _
|
|
|
|
The named global values are represented using an identifier with the '@' prefix.
|
|
If the identifier doesn't match the regular expression
|
|
`[-a-zA-Z$._][-a-zA-Z$._0-9]*`, then this identifier must be quoted.
|
|
|
|
The unnamed global values are represented using an unsigned numeric value with
|
|
the '@' prefix, like in the following examples: ``@0``, ``@989``.
|
|
|
|
.. TODO: Describe the parsers default behaviour when optional YAML attributes
|
|
are missing.
|
|
.. TODO: Describe the syntax for the bundled instructions.
|
|
.. TODO: Describe the syntax for virtual register YAML definitions.
|
|
.. TODO: Describe the machine function's YAML flag attributes.
|
|
.. TODO: Describe the syntax for the external symbol and register
|
|
mask machine operands.
|
|
.. TODO: Describe the frame information YAML mapping.
|
|
.. TODO: Describe the syntax of the stack object machine operands and their
|
|
YAML definitions.
|
|
.. TODO: Describe the syntax of the constant pool machine operands and their
|
|
YAML definitions.
|
|
.. TODO: Describe the syntax of the jump table machine operands and their
|
|
YAML definitions.
|
|
.. TODO: Describe the syntax of the block address machine operands.
|
|
.. TODO: Describe the syntax of the CFI index machine operands.
|
|
.. TODO: Describe the syntax of the metadata machine operands, and the
|
|
instructions debug location attribute.
|
|
.. TODO: Describe the syntax of the target index machine operands.
|
|
.. TODO: Describe the syntax of the register live out machine operands.
|
|
.. TODO: Describe the syntax of the machine memory operands.
|