Revert r314879 "[UnreachableBlockElim] Use COPY if PHI input is undef"

Build-bots broke on the new testcase. I'll investigate and fix.

llvm-svn: 314880

1 files changed, 2 insertions, 3 deletions

diff --git a/llvm/lib/CodeGen/UnreachableBlockElim.cpp b/llvm/lib/CodeGen/UnreachableBlockElim.cpp
index bdd25f29aea..407fd9b162e 100644
--- a/llvm/lib/CodeGen/UnreachableBlockElim.cpp
+++ b/llvm/lib/CodeGen/UnreachableBlockElim.cpp
@@ -207,12 +207,11 @@ bool UnreachableMachineBlockElim::runOnMachineFunction(MachineFunction &F) {
           MachineRegisterInfo &MRI = F.getRegInfo();
           unsigned InputSub = Input.getSubReg();
           if (InputSub == 0 &&
-              MRI.constrainRegClass(InputReg, MRI.getRegClass(OutputReg)) &&
-              !Input.isUndef()) {
+              MRI.constrainRegClass(InputReg, MRI.getRegClass(OutputReg))) {
             MRI.replaceRegWith(OutputReg, InputReg);
           } else {
             // The input register to the PHI has a subregister or it can't be
-            // constrained to the proper register class or it is undef:
+            // constrained to the proper register class:
             // insert a COPY instead of simply replacing the output
             // with the input.
             const TargetInstrInfo *TII = F.getSubtarget().getInstrInfo();