Summary:
This intrinsic lets us set inactive lanes to an identity value when
implementing wavefront reductions. In combination with Whole Wavefront
Mode, it lets inactive lanes be skipped over as required by GLSL/Vulkan.
Lowering the intrinsic needs to happen post-RA so that RA knows that the
destination isn't completely overwritten due to the EXEC shenanigans, so
we need another pseudo-instruction to represent the un-lowered
intrinsic.
Reviewers: tstellar, arsenm
Subscribers: kzhuravl, wdng, nhaehnle, yaxunl, dstuttard, tpr, t-tye
Differential Revision: https://reviews.llvm.org/D34719
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@310088 91177308-0d34-0410-b5e6-96231b3b80d8
Summary:
Whole Wavefront Wode (WWM) is similar to WQM, except that all of the
lanes are always enabled, regardless of control flow. This is required
for implementing wavefront reductions in non-uniform control flow, where
we need to use the inactive lanes to propagate intermediate results, so
they need to be enabled. We need to propagate WWM to uses (unless
they're explicitly marked as exact) so that they also propagate
intermediate results correctly. We do the analysis and exec mask munging
during the WQM pass, since there are interactions with WQM for things
that require both WQM and WWM. For simplicity, WWM is entirely
block-local -- blocks are never WWM on entry or exit of a block, and WWM
is not propagated to the block level. This means that computations
involving WWM cannot involve control flow, but we only ever plan to use
WWM for a few limited purposes (none of which involve control flow)
anyways.
Shaders can ask for WWM using the @llvm.amdgcn.wwm intrinsic. There
isn't yet a way to turn WWM off -- that will be added in a future
change.
Finally, it turns out that turning on inactive lanes causes a number of
problems with register allocation. While the best long-term solution
seems like teaching LLVM's register allocator about predication, for now
we need to add some hacks to prevent ourselves from getting into trouble
due to constraints that aren't currently expressed in LLVM. For the gory
details, see the comments at the top of SIFixWWMLiveness.cpp.
Reviewers: arsenm, nhaehnle, tpr
Subscribers: kzhuravl, wdng, mgorny, yaxunl, dstuttard, t-tye, llvm-commits
Differential Revision: https://reviews.llvm.org/D35524
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@310087 91177308-0d34-0410-b5e6-96231b3b80d8
Summary:
Previously, we assumed that certain types of instructions needed WQM in
pixel shaders, particularly DS instructions and image sampling
instructions. This was ok because with OpenGL, the assumption was
correct. But we want to start using DPP instructions for derivatives as
well as other things, so the assumption that we can infer whether to use
WQM based on the instruction won't continue to hold. This intrinsic lets
frontends like Mesa indicate what things need WQM based on their
knowledge of the API, rather than second-guessing them in the backend.
We need to keep around the old method of enabling WQM, but eventually we
should remove it once Mesa catches up. For now, this will let us use DPP
instructions for computing derivatives correctly.
Reviewers: arsenm, tpr, nhaehnle
Subscribers: kzhuravl, wdng, yaxunl, dstuttard, llvm-commits, t-tye
Differential Revision: https://reviews.llvm.org/D35167
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@310085 91177308-0d34-0410-b5e6-96231b3b80d8
An encoding does not allow to use SDWA in an instruction with
scalar operands, either literals or SGPRs. That is however possible
to copy these operands into a VGPR first.
Several copies of the value are produced if multiple SDWA conversions
were done. To cleanup MachineLICM (to hoist copies out of loops),
MachineCSE (to remove duplicate copies) and SIFoldOperands (to replace
SGPR to VGPR copy with immediate copy right to the VGPR) runs are added
after the SDWA pass.
Differential Revision: https://reviews.llvm.org/D33583
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@304219 91177308-0d34-0410-b5e6-96231b3b80d8
This allows us to ensure that 0 is never a valid pointer
to a user object, and ensures that the offset is always legal
without needing a register to access it. This comes at the cost
of usable offsets and wasted stack space.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@295877 91177308-0d34-0410-b5e6-96231b3b80d8
addSchedBarrierDeps() is supposed to add use operands to the ExitSU
node. The current implementation adds uses for calls/barrier instruction
and the MBB live-outs in all other cases. The use
operands of conditional jump instructions were missed.
Also added code to macrofusion to set the latencies between nodes to
zero to avoid problems with the fusing nodes lingering around in the
pending list now.
Differential Revision: https://reviews.llvm.org/D25140
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@286544 91177308-0d34-0410-b5e6-96231b3b80d8
The comment explaining why this was necessary is incorrect
in its description of v_cmp's behavior for inactive workitems.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@286134 91177308-0d34-0410-b5e6-96231b3b80d8
It's possible to have a use of the private resource descriptor or
scratch wave offset registers even though there are no allocated
stack objects. This would result in continuing to use the maximum
number reserved registers. This could go over the number of SGPRs
available on VI, or violate the SGPR limit requested by
the function attributes.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@285435 91177308-0d34-0410-b5e6-96231b3b80d8
Summary:
This contains two changes that reduce the time spent in WQM, with the
intention of reducing bandwidth required by VMEM loads:
1. Sampling instructions by themselves don't need to run in WQM, only their
coordinate inputs need it (unless of course there is a dependent sampling
instruction). The initial scanInstructions step is modified accordingly.
2. When switching back from WQM to Exact, switch back as soon as possible.
This affects the logic in processBlock.
This should always be a win or at best neutral.
There are also some cleanups (e.g. remove unused ExecExports) and some new
debugging output.
Reviewers: arsenm, tstellarAMD, mareko
Subscribers: arsenm, llvm-commits, kzhuravl
Differential Revision: http://reviews.llvm.org/D22092
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@280590 91177308-0d34-0410-b5e6-96231b3b80d8
Summary:
This fixes a rare bug in polygon stippling with non-monolithic pixel shaders.
The underlying problem is as follows: the prolog part contains the polygon
stippling sequence, i.e. a kill. The main part then enables WQM based on the
_reduced_ exec mask, effectively undoing most of the polygon stippling.
Since we cannot know whether polygon stippling will be used, the main part
of a non-monolithic shader must always return to exact mode to fix this
problem.
Reviewers: arsenm, tstellarAMD, mareko
Subscribers: arsenm, llvm-commits, kzhuravl
Differential Revision: https://reviews.llvm.org/D23131
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@280589 91177308-0d34-0410-b5e6-96231b3b80d8
Summary:
We need to use floating-point compares to ensure that s_cbranch_vcc*
instructions are always generated. With integer compares, future
optimizations could cause s_cbranch_scc* to be generated instead.
Reviewers: arsenm, nhaehnle
Subscribers: llvm-commits, kzhuravl
Differential Revision: https://reviews.llvm.org/D23401
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@279148 91177308-0d34-0410-b5e6-96231b3b80d8
If a loop is not rotated (for example when optimizing for size), the latch is not the backedge. If we promote an expression to post-inc form, we not only increase register pressure and add a COPY for that IV expression but for all IVs!
Motivating testcase:
void f(float *a, float *b, float *c, int n) {
while (n-- > 0)
*c++ = *a++ + *b++;
}
It's imperative that the pointer increments be located in the latch block and not the header block; if not, we cannot use post-increment loads and stores and we have to keep both the post-inc and pre-inc values around until the end of the latch which bloats register usage.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@278658 91177308-0d34-0410-b5e6-96231b3b80d8
Insert before the skip branch if one is created.
This is a somewhat more natural placement relative
to the skip branches, and makes it possible to implement
analyzeBranch for skip blocks.
The test changes are mostly due to a quirk where
the block label is not emitted if there is a terminator
that is not also a branch.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@278273 91177308-0d34-0410-b5e6-96231b3b80d8
Summary:
Two types of stores are possible in pixel shaders: stores to memory that are
explicitly requested at the API level, and stores that are an implementation
detail of register spilling or lowering of arrays.
For the first kind of store, we must ensure that helper pixels have no effect
and hence WQM must be disabled. The second kind of store must always be
executed, because the written value may be loaded again in a way that is
relevant for helper pixels as well -- and there are no externally visible
effects anyway.
This is a candidate for the 3.9 release branch.
Reviewers: arsenm, tstellarAMD, mareko
Subscribers: arsenm, kzhuravl, llvm-commits
Differential Revision: https://reviews.llvm.org/D22675
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@277504 91177308-0d34-0410-b5e6-96231b3b80d8
Summary:
There are cases where uniform branch conditions are computed in VGPRs, and
we didn't correctly mark those as WQM.
The stray change in basic-branch.ll is because invoking the LiveIntervals
analysis leads to the detection of a dead register that would otherwise not
be seen at -O0.
This is a candidate for the 3.9 branch, as it fixes a possible hang.
Reviewers: arsenm, tstellarAMD, mareko
Subscribers: arsenm, llvm-commits, kzhuravl
Differential Revision: https://reviews.llvm.org/D22673
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@277500 91177308-0d34-0410-b5e6-96231b3b80d8
The main sin this was committing was using terminator
instructions in the middle of the block, and then
not updating the block successors / predecessors.
Split the blocks up to avoid this and introduce new
pseudo instructions for branches taken with exec masking.
Also use a pseudo instead of emitting s_endpgm and erasing
it in the special case of a non-void return.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@273467 91177308-0d34-0410-b5e6-96231b3b80d8
Summary:
The presence of this attribute indicates that VGPR outputs should be computed
in whole quad mode. This will be used by Mesa for prolog pixel shaders, so
that derivatives can be taken of shader inputs computed by the prolog, fixing
a bug.
The generated code could certainly be improved: if a prolog pixel shader is
used (which isn't common in modern OpenGL - they're used for gl_Color, polygon
stipples, and forcing per-sample interpolation), Mesa will use this attribute
unconditionally, because it has to be conservative. So WQM may be used in the
prolog when it isn't really needed, and furthermore a silly back-and-forth
switch is likely to happen at the boundary between prolog and main shader
parts.
Fixing this is a bit involved: we'd first have to add a mechanism by which
LLVM writes the WQM-related input requirements to the main shader part binary,
and then Mesa specializes the prolog part accordingly. At that point, we may
as well just compile a monolithic shader...
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=95130
Reviewers: arsenm, tstellarAMD, mareko
Subscribers: arsenm, llvm-commits, kzhuravl
Differential Revision: http://reviews.llvm.org/D20839
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@272063 91177308-0d34-0410-b5e6-96231b3b80d8
Allocating larger register classes first should give better allocation
results (and more importantly for myself, make the lit tests more stable
with respect to scheduler changes).
Patch by Matthias Braun
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@270312 91177308-0d34-0410-b5e6-96231b3b80d8
Summary:
Whole quad mode is already enabled for pixel shaders that compute
derivatives, but it must be suspended for instructions that cause a
shader to have side effects (i.e. stores and atomics).
This pass addresses the issue by storing the real (initial) live mask
in a register, masking EXEC before instructions that require exact
execution and (re-)enabling WQM where required.
This pass is run before register coalescing so that we can use
machine SSA for analysis.
The changes in this patch expose a problem with the second machine
scheduling pass: target independent instructions like COPY implicitly
use EXEC when they operate on VGPRs, but this fact is not encoded in
the MIR. This can lead to miscompilation because instructions are
moved past changes to EXEC.
This patch fixes the problem by adding use-implicit operands to
target independent instructions. Some general codegen passes are
relaxed to work with such implicit use operands.
Reviewers: arsenm, tstellarAMD, mareko
Subscribers: MatzeB, arsenm, llvm-commits
Differential Revision: http://reviews.llvm.org/D18162
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@263982 91177308-0d34-0410-b5e6-96231b3b80d8
