[llvm] [PHIElimination] Reuse existing COPY in predecessor basic block (PR #131837)

[Mikael Holmén via llvm-commits]

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@@ -581,6 +581,15 @@ void PHIEliminationImpl::LowerPHINode(MachineBasicBlock &MBB,
       continue;
     }
 
+    // Reuse an existing copy in the block if possible.
+    if (MachineInstr *DefMI = MRI->getUniqueVRegDef(SrcReg)) {
+      if (DefMI->isCopy() && DefMI->getParent() == &opBlock &&
+          MRI->use_empty(SrcReg)) {
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mikaelholmen wrote:

@guy-david 
Can you please do take care of this?

We don't want the presence of debug instructions to affect code generation.

https://github.com/llvm/llvm-project/pull/131837