[llvm] [MachineCopyPropagation] Recognise and delete no-op moves produced after forwarded uses (PR #129889)

[Philip Reames via llvm-commits]

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@@ -971,6 +971,18 @@ void MachineCopyPropagation::ForwardCopyPropagateBlock(MachineBasicBlock &MBB) {
 
     forwardUses(MI);
 
+    // It's possible that the previous transformation has resulted in a no-op
+    // register move (i.e. one where source and destination registers are the
+    // same). If so, delete it.
+    CopyOperands = isCopyInstr(MI, *TII, UseCopyInstr);
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preames wrote:

Placement wise, I think this works better as an if before the existing !TRI->regsOverlap(RegDef, RegSrc) check specific for copies above.  Purely a stylistic comment.

https://github.com/llvm/llvm-project/pull/129889