Re-apply r175688, with the changes suggested by Jakob in PR15320.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@175809 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 15 insertions, 24 deletions

diff --git a/lib/CodeGen/ExpandPostRAPseudos.cpp b/lib/CodeGen/ExpandPostRAPseudos.cpp
index 0b9e83d6cd..1611db8d91 100644
--- a/lib/CodeGen/ExpandPostRAPseudos.cpp
+++ b/lib/CodeGen/ExpandPostRAPseudos.cpp
@@ -49,8 +49,6 @@ private:
   bool LowerSubregToReg(MachineInstr *MI);
   bool LowerCopy(MachineInstr *MI);
 
-  void TransferDeadFlag(MachineInstr *MI, unsigned DstReg,
-                        const TargetRegisterInfo *TRI);
   void TransferImplicitDefs(MachineInstr *MI);
 };
 } // end anonymous namespace
@@ -61,21 +59,6 @@ char &llvm::ExpandPostRAPseudosID = ExpandPostRA::ID;
 INITIALIZE_PASS(ExpandPostRA, "postrapseudos",
                 "Post-RA pseudo instruction expansion pass", false, false)
 
-/// TransferDeadFlag - MI is a pseudo-instruction with DstReg dead,
-/// and the lowered replacement instructions immediately precede it.
-/// Mark the replacement instructions with the dead flag.
-void
-ExpandPostRA::TransferDeadFlag(MachineInstr *MI, unsigned DstReg,
-                               const TargetRegisterInfo *TRI) {
-  for (MachineBasicBlock::iterator MII =
-        prior(MachineBasicBlock::iterator(MI)); ; --MII) {
-    if (MII->addRegisterDead(DstReg, TRI))
-      break;
-    assert(MII != MI->getParent()->begin() &&
-           "copyPhysReg output doesn't reference destination register!");
-  }
-}
-
 /// TransferImplicitDefs - MI is a pseudo-instruction, and the lowered
 /// replacement instructions immediately precede it.  Copy any implicit-def
 /// operands from MI to the replacement instruction.
@@ -114,6 +97,12 @@ bool ExpandPostRA::LowerSubregToReg(MachineInstr *MI) {
 
   DEBUG(dbgs() << "subreg: CONVERTING: " << *MI);
 
+  if (MI->allDefsAreDead()) {
+    MI->setDesc(TII->get(TargetOpcode::KILL));
+    DEBUG(dbgs() << "subreg: replaced by: " << *MI);
+    return true;
+  }
+
   if (DstSubReg == InsReg) {
     // No need to insert an identify copy instruction.
     // Watch out for case like this:
@@ -135,10 +124,6 @@ bool ExpandPostRA::LowerSubregToReg(MachineInstr *MI) {
     MachineBasicBlock::iterator CopyMI = MI;
     --CopyMI;
     CopyMI->addRegisterDefined(DstReg);
-
-    // Transfer the kill/dead flags, if needed.
-    if (MI->getOperand(0).isDead())
-      TransferDeadFlag(MI, DstSubReg, TRI);
     DEBUG(dbgs() << "subreg: " << *CopyMI);
   }
 
@@ -148,6 +133,14 @@ bool ExpandPostRA::LowerSubregToReg(MachineInstr *MI) {
 }
 
 bool ExpandPostRA::LowerCopy(MachineInstr *MI) {
+
+  if (MI->allDefsAreDead()) {
+    DEBUG(dbgs() << "dead copy: " << *MI);
+    MI->setDesc(TII->get(TargetOpcode::KILL));
+    DEBUG(dbgs() << "replaced by: " << *MI);
+    return true;
+  }
+
   MachineOperand &DstMO = MI->getOperand(0);
   MachineOperand &SrcMO = MI->getOperand(1);
 
@@ -155,7 +148,7 @@ bool ExpandPostRA::LowerCopy(MachineInstr *MI) {
     DEBUG(dbgs() << "identity copy: " << *MI);
     // No need to insert an identity copy instruction, but replace with a KILL
     // if liveness is changed.
-    if (DstMO.isDead() || SrcMO.isUndef() || MI->getNumOperands() > 2) {
+    if (SrcMO.isUndef() || MI->getNumOperands() > 2) {
       // We must make sure the super-register gets killed. Replace the
       // instruction with KILL.
       MI->setDesc(TII->get(TargetOpcode::KILL));
@@ -171,8 +164,6 @@ bool ExpandPostRA::LowerCopy(MachineInstr *MI) {
   TII->copyPhysReg(*MI->getParent(), MI, MI->getDebugLoc(),
                    DstMO.getReg(), SrcMO.getReg(), SrcMO.isKill());
 
-  if (DstMO.isDead())
-    TransferDeadFlag(MI, DstMO.getReg(), TRI);
   if (MI->getNumOperands() > 2)
     TransferImplicitDefs(MI);
   DEBUG({