Teach MachineLICM and MachineSink how to clear kill flags conservatively

when they move instructions.

llvm-svn: 103737

3 files changed, 27 insertions, 1 deletions

diff --git a/llvm/lib/CodeGen/MachineInstr.cpp b/llvm/lib/CodeGen/MachineInstr.cpp
index 99b5beb1365..d909fb0ef3e 100644
--- a/llvm/lib/CodeGen/MachineInstr.cpp
+++ b/llvm/lib/CodeGen/MachineInstr.cpp
@@ -938,6 +938,16 @@ isRegTiedToDefOperand(unsigned UseOpIdx, unsigned *DefOpIdx) const {
   return true;
 }
 
+/// clearKillInfo - Clears kill flags on all operands.
+///
+void MachineInstr::clearKillInfo() {
+  for (unsigned i = 0, e = getNumOperands(); i != e; ++i) {
+    MachineOperand &MO = getOperand(i);
+    if (MO.isReg() && MO.isUse())
+      MO.setIsKill(false);
+  }
+}
+
 /// copyKillDeadInfo - Copies kill / dead operand properties from MI.
 ///
 void MachineInstr::copyKillDeadInfo(const MachineInstr *MI) {
diff --git a/llvm/lib/CodeGen/MachineLICM.cpp b/llvm/lib/CodeGen/MachineLICM.cpp
index b2e757d8d65..61206173e64 100644
--- a/llvm/lib/CodeGen/MachineLICM.cpp
+++ b/llvm/lib/CodeGen/MachineLICM.cpp
@@ -738,8 +738,10 @@ bool MachineLICM::EliminateCSE(MachineInstr *MI,
              "Instructions with different phys regs are not identical!");
 
       if (MO.isReg() && MO.isDef() &&
-          !TargetRegisterInfo::isPhysicalRegister(MO.getReg()))
+          !TargetRegisterInfo::isPhysicalRegister(MO.getReg())) {
         RegInfo->replaceRegWith(MO.getReg(), Dup->getOperand(i).getReg());
+        RegInfo->clearKillFlags(Dup->getOperand(i).getReg());
+      }
     }
     MI->eraseFromParent();
     ++NumCSEed;
@@ -784,6 +786,15 @@ void MachineLICM::Hoist(MachineInstr *MI) {
     // Otherwise, splice the instruction to the preheader.
     CurPreheader->splice(CurPreheader->getFirstTerminator(),MI->getParent(),MI);
 
+    // Clear the kill flags of any register this instruction defines,
+    // since they may need to be live throughout the entire loop
+    // rather than just live for part of it.
+    for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
+      MachineOperand &MO = MI->getOperand(i);
+      if (MO.isReg() && MO.isDef() && !MO.isDead())
+        RegInfo->clearKillFlags(MO.getReg());
+    }
+
     // Add to the CSE map.
     if (CI != CSEMap.end())
       CI->second.push_back(MI);
diff --git a/llvm/lib/CodeGen/MachineSink.cpp b/llvm/lib/CodeGen/MachineSink.cpp
index ef489dc5560..1610e6c9610 100644
--- a/llvm/lib/CodeGen/MachineSink.cpp
+++ b/llvm/lib/CodeGen/MachineSink.cpp
@@ -314,5 +314,10 @@ bool MachineSinking::SinkInstruction(MachineInstr *MI, bool &SawStore) {
   // Move the instruction.
   SuccToSinkTo->splice(InsertPos, ParentBlock, MI,
                        ++MachineBasicBlock::iterator(MI));
+
+  // Conservatively, clear any kill flags, since it's possible that
+  // they are no longer correct.
+  MI->clearKillInfo();
+
   return true;
 }