[PATCH] D49288: [AMDGPU] run post-RA hazard recognizer pass after memory legalizer, waitcnt passes

[Matt Arsenault via Phabricator via llvm-commits]

arsenm added inline comments.


================
Comment at: lib/Target/AMDGPU/AMDGPUTargetMachine.cpp:902
 
-  addPass(createSIMemoryLegalizerPass());
-  addPass(createSIInsertWaitcntsPass());
   addPass(createSIShrinkInstructionsPass());
   addPass(&SIInsertSkipsPassID);
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I'm surprised we run shrink after this point.

I think this can plausibly be an issue.
Suppose you had something like
%vgpr0 = V_FOO
<some hazard>
%vgpr1 = V_MOV_B32 5
%vgpr2 = V_BAR %vgpr1

The immediate materialize would eliminate a wait state that wasn't necessary, but now is since the copy is eliminated.  I think in practice the shrink pass isn't very good at folding immediates post-RA, if it even tries


https://reviews.llvm.org/D49288