1 files changed, 16 insertions, 2 deletions
diff --git a/llvm/lib/CodeGen/RegisterCoalescer.cpp b/llvm/lib/CodeGen/RegisterCoalescer.cpp
index c067d87a9fd8..c1af37c8510f 100644
--- a/llvm/lib/CodeGen/RegisterCoalescer.cpp
+++ b/llvm/lib/CodeGen/RegisterCoalescer.cpp
@@ -1201,6 +1201,8 @@ bool RegisterCoalescer::removePartialRedundancy(const CoalescerPair &CP,
                       << printMBBReference(MBB) << '\t' << CopyMI);
   }
 
+  const bool IsUndefCopy = CopyMI.getOperand(1).isUndef();
+
   // Remove CopyMI.
   // Note: This is fine to remove the copy before updating the live-ranges.
   // While updating the live-ranges, we only look at slot indices and
@@ -1214,6 +1216,19 @@ bool RegisterCoalescer::removePartialRedundancy(const CoalescerPair &CP,
   LIS->pruneValue(*static_cast<LiveRange *>(&IntB), CopyIdx.getRegSlot(),
                   &EndPoints);
   BValNo->markUnused();
+
+  if (IsUndefCopy) {
+    // We're introducing an undef phi def, and need to set undef on any users of
+    // the previously local def to avoid artifically extending the lifetime
+    // through the block.
+    for (MachineOperand &MO : MRI->use_nodbg_operands(IntB.reg())) {
+      const MachineInstr &MI = *MO.getParent();
+      SlotIndex UseIdx = LIS->getInstructionIndex(MI);
+      if (!IntB.liveAt(UseIdx))
+        MO.setIsUndef(true);
+    }
+  }
+
   // Extend IntB to the EndPoints of its original live interval.
   LIS->extendToIndices(IntB, EndPoints);
 
@@ -1596,8 +1611,7 @@ bool RegisterCoalescer::reMaterializeTrivialDef(const CoalescerPair &CP,
         LR->createDeadDef(NewMIIdx.getRegSlot(), LIS->getVNInfoAllocator());
   }
 
-  if (NewMI.getOperand(0).getSubReg())
-    NewMI.getOperand(0).setIsUndef();
+  NewMI.setRegisterDefReadUndef(NewMI.getOperand(0).getReg());
 
   // Transfer over implicit operands to the rematerialized instruction.
   for (MachineOperand &MO : ImplicitOps)