[llvm] [AMDGPU] Remove redundant s_cmp_lg_* sX, 0 (PR #162352)

[via llvm-commits]

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@@ -10608,6 +10608,73 @@ bool SIInstrInfo::optimizeCompareInstr(MachineInstr &CmpInstr, Register SrcReg,
   if (SrcReg2 && !getFoldableImm(SrcReg2, *MRI, CmpValue))
     return false;
 
+  const auto optimizeCmpSelect = [&CmpInstr, SrcReg, CmpValue, MRI,
+                                  this]() -> bool {
+    if (CmpValue != 0)
+      return false;
+
+    MachineInstr *Def = MRI->getUniqueVRegDef(SrcReg);
+    if (!Def || Def->getParent() != CmpInstr.getParent())
+      return false;
+
+    if (!(Def->getOpcode() == AMDGPU::S_LSHL_B32 ||
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LU-JOHN wrote:

It should be all instructions that set SCC = DST!=0.  s_max/s_min are excluded since they set SCC but with a different condition.  I need to review the list since I missed some instructions that should be included (e.g. s_absdiff).

https://github.com/llvm/llvm-project/pull/162352