[llvm-branch-commits] [llvm] PeepholeOpt: Fix losing subregister indexes on full copies (PR #161310)

[Jay Foad via llvm-branch-commits]

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@@ -1905,7 +1905,28 @@ ValueTrackerResult ValueTracker::getNextSourceFromCopy() {
   const MachineOperand &Src = Def->getOperand(1);
   if (Src.isUndef())
     return ValueTrackerResult();
-  return ValueTrackerResult(Src.getReg(), Src.getSubReg());
+
+  Register SrcReg = Src.getReg();
+  unsigned SubReg = Src.getSubReg();
+  if (DefSubReg) {
+    const TargetRegisterInfo *TRI = MRI.getTargetRegisterInfo();
+    SubReg = TRI->composeSubRegIndices(SubReg, DefSubReg);
+    if (SubReg) {
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jayfoad wrote:

I don't think SubReg can ever be 0 here, since you previously checked that DefSubReg is not 0.

https://github.com/llvm/llvm-project/pull/161310