X86 Peephole: fix PR13475 in optimizeCompare.
It is possible that an instruction can use and update EFLAGS.
When checking the safety, we should check the usage of EFLAGS first before
declaring it is safe to optimize due to the update.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@160912 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Target/X86/X86InstrInfo.cpp b/lib/Target/X86/X86InstrInfo.cpp
index 69493bc..89a57b5 100644
--- a/lib/Target/X86/X86InstrInfo.cpp
+++ b/lib/Target/X86/X86InstrInfo.cpp
@@ -3221,12 +3221,15 @@
MachineBasicBlock::iterator E = CmpInstr->getParent()->end();
for (++I; I != E; ++I) {
const MachineInstr &Instr = *I;
- if (Instr.modifiesRegister(X86::EFLAGS, TRI)) {
+ bool ModifyEFLAGS = Instr.modifiesRegister(X86::EFLAGS, TRI);
+ bool UseEFLAGS = Instr.readsRegister(X86::EFLAGS, TRI);
+ // We should check the usage if this instruction uses and updates EFLAGS.
+ if (!UseEFLAGS && ModifyEFLAGS) {
// It is safe to remove CmpInstr if EFLAGS is updated again.
IsSafe = true;
break;
}
- if (!Instr.readsRegister(X86::EFLAGS, TRI))
+ if (!UseEFLAGS && !ModifyEFLAGS)
continue;
// EFLAGS is used by this instruction.
@@ -3281,7 +3284,8 @@
// instructions will be modified.
OpsToUpdate.push_back(std::make_pair(&*I, NewOpc));
}
- if (Instr.killsRegister(X86::EFLAGS, TRI)) {
+ if (ModifyEFLAGS || Instr.killsRegister(X86::EFLAGS, TRI)) {
+ // It is safe to remove CmpInstr if EFLAGS is updated again or killed.
IsSafe = true;
break;
}