[X86] Properly check that EAX is dead when copying EFLAGS.
This fixes a bug introduced in r267623, where we got smarter and avoided to save
EAX before using it. However, we failed to check if any of the subregister of
EAX were alive and thus, missed cases where we have to save EAX before using it.
The problem may happen on every X86/i386/... platform.
This fixes llvm.org/PR27624
llvm-svn: 269115
diff --git a/llvm/lib/Target/X86/X86InstrInfo.cpp b/llvm/lib/Target/X86/X86InstrInfo.cpp
index f6c11c8..11c532c 100644
--- a/llvm/lib/Target/X86/X86InstrInfo.cpp
+++ b/llvm/lib/Target/X86/X86InstrInfo.cpp
@@ -4527,8 +4527,9 @@
// first frame index.
// See X86ISelLowering.cpp - X86::hasCopyImplyingStackAdjustment.
+ const TargetRegisterInfo *TRI = &getRegisterInfo();
MachineBasicBlock::LivenessQueryResult LQR =
- MBB.computeRegisterLiveness(&getRegisterInfo(), AX, MI);
+ MBB.computeRegisterLiveness(TRI, AX, MI);
// We do not want to save and restore AX if we do not have to.
// Moreover, if we do so whereas AX is dead, we would need to set
// an undef flag on the use of AX, otherwise the verifier will
@@ -4536,15 +4537,19 @@
// We do not want to change the behavior of the machine verifier
// as this is usually wrong to read an undef value.
if (MachineBasicBlock::LQR_Unknown == LQR) {
- LivePhysRegs LPR(&getRegisterInfo());
+ LivePhysRegs LPR(TRI);
LPR.addLiveOuts(MBB);
MachineBasicBlock::iterator I = MBB.end();
while (I != MI) {
--I;
LPR.stepBackward(*I);
}
- LQR = LPR.contains(AX) ? MachineBasicBlock::LQR_Live
- : MachineBasicBlock::LQR_Dead;
+ // AX contains the top most register in the aliasing hierarchy.
+ // It may not be live, but one of its aliases may be.
+ for (MCRegAliasIterator AI(AX, TRI, true);
+ AI.isValid() && LQR != MachineBasicBlock::LQR_Live; ++AI)
+ LQR = LPR.contains(*AI) ? MachineBasicBlock::LQR_Live
+ : MachineBasicBlock::LQR_Dead;
}
bool AXDead = (Reg == AX) || (MachineBasicBlock::LQR_Dead == LQR);
if (!AXDead)