[PATCH] D96336: [AMDGPU] Save VGPR of whole wave when spilling

[Sebastian Neubauer via Phabricator via llvm-commits]

sebastian-ne updated this revision to Diff 335796.
sebastian-ne added a comment.

Merged with D96517 <https://reviews.llvm.org/D96517> and rewritten.
I hope the new version is easier to understand and creates better code.

I tried using scavengeRegisterBackwards, but it turned out that the RegScavenger is in forward mode, so we would need to switch back and forth. Also, scavenging backwards does not necessarily coincide with the liveness information, which was the main point of using the scavenger here.

The largest performance hit of this change is the s_waitcnt after restoring the temporary VGPR.
We do need to add a use of the load somewhere, otherwise it can be eliminated. I tried marking the load as volatile, which prevents it from being removed, but that also adds an s_waitcnt straight after the load.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D96336/new/

https://reviews.llvm.org/D96336

Files:
  llvm/lib/Target/AMDGPU/GCNSubtarget.h
  llvm/lib/Target/AMDGPU/SIFrameLowering.cpp
  llvm/lib/Target/AMDGPU/SIMachineFunctionInfo.cpp
  llvm/lib/Target/AMDGPU/SIMachineFunctionInfo.h
  llvm/lib/Target/AMDGPU/SIRegisterInfo.cpp
  llvm/lib/Target/AMDGPU/SIRegisterInfo.h
  llvm/test/CodeGen/AMDGPU/control-flow-fastregalloc.ll
  llvm/test/CodeGen/AMDGPU/frame-setup-without-sgpr-to-vgpr-spills.ll
  llvm/test/CodeGen/AMDGPU/partial-sgpr-to-vgpr-spills.ll
  llvm/test/CodeGen/AMDGPU/sgpr-spill.mir
  llvm/test/CodeGen/AMDGPU/si-spill-sgpr-stack.ll
  llvm/test/CodeGen/AMDGPU/spill-m0.ll
  llvm/test/CodeGen/AMDGPU/spill-scavenge-offset.ll
  llvm/test/CodeGen/AMDGPU/spill-special-sgpr.mir

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