1 files changed, 5 insertions, 1 deletions
diff --git a/llvm/lib/CodeGen/OptimizePHIs.cpp b/llvm/lib/CodeGen/OptimizePHIs.cpp
index c05be130ec61..85fa04180088 100644
--- a/llvm/lib/CodeGen/OptimizePHIs.cpp
+++ b/llvm/lib/CodeGen/OptimizePHIs.cpp
@@ -165,7 +165,11 @@ bool OptimizePHIs::OptimizeBB(MachineBasicBlock &MBB) {
     InstrSet PHIsInCycle;
     if (IsSingleValuePHICycle(MI, SingleValReg, PHIsInCycle) &&
         SingleValReg != 0) {
-      MRI->replaceRegWith(MI->getOperand(0).getReg(), SingleValReg);
+      unsigned OldReg = MI->getOperand(0).getReg();
+      if (!MRI->constrainRegClass(SingleValReg, MRI->getRegClass(OldReg)))
+        continue;
+
+      MRI->replaceRegWith(OldReg, SingleValReg);
       MI->eraseFromParent();
       ++NumPHICycles;
       Changed = true;