2 files changed, 16 insertions, 5 deletions

diff --git a/llvm/lib/CodeGen/IfConversion.cpp b/llvm/lib/CodeGen/IfConversion.cpp
index 3ac78b25854..5df18fbe199 100644
--- a/llvm/lib/CodeGen/IfConversion.cpp
+++ b/llvm/lib/CodeGen/IfConversion.cpp
@@ -980,10 +980,10 @@ static void UpdatePredRedefs(MachineInstr *MI, LivePhysRegs &Redefs) {
 
   // Now add the implicit uses for each of the clobbered values.
   for (auto Reg : Clobbers) {
-    const MachineOperand &Op = *Reg.second;
     // FIXME: Const cast here is nasty, but better than making StepForward
     // take a mutable instruction instead of const.
-    MachineInstr *OpMI = const_cast<MachineInstr*>(Op.getParent());
+    MachineOperand &Op = const_cast<MachineOperand&>(*Reg.second);
+    MachineInstr *OpMI = Op.getParent();
     MachineInstrBuilder MIB(*OpMI->getParent()->getParent(), OpMI);
     if (Op.isRegMask()) {
       // First handle regmasks.  They clobber any entries in the mask which
@@ -999,6 +999,12 @@ static void UpdatePredRedefs(MachineInstr *MI, LivePhysRegs &Redefs) {
       continue;
     }
     assert(Op.isReg() && "Register operand required");
+    if (Op.isDead()) {
+      // If we found a dead def, but it needs to be live, then remove the dead
+      // flag.
+      if (Redefs.contains(Op.getReg()))
+        Op.setIsDead(false);
+    }
     MIB.addReg(Reg.first, RegState::Implicit | RegState::Undef);
   }
 }
diff --git a/llvm/lib/CodeGen/LivePhysRegs.cpp b/llvm/lib/CodeGen/LivePhysRegs.cpp
index b6369275051..eef7643367f 100644
--- a/llvm/lib/CodeGen/LivePhysRegs.cpp
+++ b/llvm/lib/CodeGen/LivePhysRegs.cpp
@@ -77,8 +77,9 @@ void LivePhysRegs::stepForward(const MachineInstr &MI,
       if (Reg == 0)
         continue;
       if (O->isDef()) {
-        if (!O->isDead())
-          Clobbers.push_back(std::make_pair(Reg, &*O));
+        // Note, dead defs are still recorded.  The caller should decide how to
+        // handle them.
+        Clobbers.push_back(std::make_pair(Reg, &*O));
       } else {
         if (!O->isKill())
           continue;
@@ -90,8 +91,12 @@ void LivePhysRegs::stepForward(const MachineInstr &MI,
   }
 
   // Add defs to the set.
-  for (auto Reg : Clobbers)
+  for (auto Reg : Clobbers) {
+    // Skip dead defs.  They shouldn't be added to the set.
+    if (Reg.second->isReg() && Reg.second->isDead())
+      continue;
     addReg(Reg.first);
+  }
 }
 
 /// Prin the currently live registers to OS.