[llvm] X86: Remove stale EFLAGS live range when converting ADD to LEA (PR #222029)

[Matt Arsenault via llvm-commits]

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@@ -2042,7 +2046,11 @@ MachineInstr *X86InstrInfo::convertToThreeAddress(MachineInstr &MI,
   MBB.insert(MI.getIterator(), NewMI); // Insert the new inst
 
   if (LIS) {
+    // The replacement does not define EFLAGS; drop the dead EFLAGS def MI had.
+    SlotIndex Idx = LIS->getInstructionIndex(MI);
     LIS->ReplaceMachineInstrInMaps(MI, *NewMI);
+
+    LIS->removePhysRegDefAt(X86::EFLAGS, Idx.getRegSlot());
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arsenm wrote:

Yes, if there's no def removePhysRegDefAt ignores it 

https://github.com/llvm/llvm-project/pull/222029