[PATCH] D140546: [AMDGPU] Remove permlane discard vdst_in optimization from isel

Thu Dec 22 06:41:33 PST 2022

arsenm added inline comments.

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Comment at: llvm/test/CodeGen/AMDGPU/llvm.amdgcn.permlane.ll:853
   %tidx = call i32 @llvm.amdgcn.workitem.id.x()
-  %v = call i32 @llvm.amdgcn.permlane16(i32 12345, i32 %tidx, i32 %src1, i32 %src2, i1 1, i1 0)
+  %v = call i32 @llvm.amdgcn.permlane16(i32 undef, i32 %tidx, i32 %src1, i32 %src2, i1 1, i1 0)
   store i32 %v, ptr addrspace(1) %out
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foad wrote:
> arsenm wrote:
> > Should use poison
> Really? I read that "Most instructions return ‘poison’ when one of their arguments is ‘poison’" and that's not what I want here. Besides I am just mimicking InstCombine which still uses undef for this optimization.
undef is soft deprecated. Undef should be freeze poison

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D140546/new/

https://reviews.llvm.org/D140546