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[SYCL][ESIMD] Rework -O0 behavior #12612

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merged 4 commits into from
Feb 28, 2024
Merged

[SYCL][ESIMD] Rework -O0 behavior #12612

merged 4 commits into from
Feb 28, 2024

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sarnex
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@sarnex sarnex commented Feb 5, 2024

Let me first say I don't like this change and I wish we didn't have to do this, and it should only be temporary.

The root need is that the IGC VC backend does not support O0 code. It gets miscompiled and produces wrong answers and crashes. The team acknowledges this issue but does not have the resources to fix this at the moment.

From the ESIMD user POV, this is really frustrating. We decided it would be okay if they lost debuggability of device code (but retained it for host code) as long as their program runs and they get the right answer.

So the overall approach is to optimize ESIMD(Not SYCL!!) code even in O0 mode. We are actually already doing this, but this change extends it a bit.

So there are a few main changes in this PR:

  1. Don't pass -O0 to sycl-post-link. Note this option has absolutely no effect on SYCL code today, it is only checked in the ESIMD lowering code in sycl-post-link.
  2. Add a new pass to remove optnone/noinline early for ESIMD code in O0.
  3. Remove optnone/noinline from all functions if we split out ESIMD/SYCL code, and if we don't don't touch it.

All three of these steps are required to fix the tests failing with O0, if we remove any one of them we see many failures.

When running all ESIMD tests with O0, we see the following improvements:

Linux:
Today: 97 failures
With this change: 23 failures, with ~3 root causes. There are no regressions. I'll look into these later.
Windows: 
Today: 38 failures
With this change: 10 failures. There are no regressions. I'll look into these later.

Once IGC VC can actually correctly compile non-optimized code, we should revert this change.

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github-actions bot commented Feb 7, 2024

✅ With the latest revision this PR passed the C/C++ code formatter.

@sarnex
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sarnex commented Feb 7, 2024

Linux Gen12 failure is not related, failing everywhere:

Failed Tests (1):
  SYCL :: ESIMD/aot_mixed.cpp

@sarnex sarnex marked this pull request as ready for review February 7, 2024 21:14
@sarnex sarnex requested review from a team as code owners February 7, 2024 21:14
@@ -955,6 +955,8 @@ void EmitAssemblyHelper::RunOptimizationPipeline(
PB.registerPipelineStartEPCallback([&](ModulePassManager &MPM,
OptimizationLevel Level) {
MPM.addPass(ESIMDVerifierPass(LangOpts.SYCLESIMDForceStatelessMem));
if (Level == OptimizationLevel::O0)
MPM.addPass(ESIMDRemoveOptnoneNoinlinePass());
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I am okay with this ESIMD change.

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@premanandrao premanandrao left a comment

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FE changes are okay with me.

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sarnex commented Feb 21, 2024

@intel/dpcpp-esimd-reviewers @intel/dpcpp-tools-reviewers Ping, thanks!

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@maksimsab maksimsab left a comment

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LGTM.

llvm/lib/SYCLLowerIR/ESIMD/ESIMDRemoveOptnoneNoinline.cpp Outdated Show resolved Hide resolved
@@ -1834,6 +1834,15 @@ bool SYCLLowerESIMDPass::prepareForAlwaysInliner(Module &M) {
continue;
}

// If we are splitting by ESIMD, we are guarenteed the entire
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Is this code still needed after adding the special pass that remove those 2 attributes?

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Yes, I tested many combinations of with/without different changes in this PR and everything we currently have is required.

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sarnex commented Feb 28, 2024

Windows fail is not related

@sarnex sarnex merged commit 00749b1 into intel:sycl Feb 28, 2024
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6 participants