if (!Sub)
return false;
+ bool IsSwapped = (SrcReg2 != 0 && Sub->getOperand(1).getReg() == SrcReg2 &&
+ Sub->getOperand(2).getReg() == SrcReg);
+
// Scan forward from the instruction after CmpInstr for uses of EFLAGS.
+ // It is safe to remove CmpInstr if EFLAGS is redefined or killed.
+ // If we are done with the basic block, we need to check whether EFLAGS is
+ // live-out.
+ bool IsSafe = false;
SmallVector<std::pair<MachineInstr*, unsigned /*NewOpc*/>, 4> OpsToUpdate;
MachineBasicBlock::iterator E = CmpInstr->getParent()->end();
for (++I; I != E; ++I) {
const MachineInstr &Instr = *I;
- if (Instr.modifiesRegister(X86::EFLAGS, TRI))
+ if (Instr.modifiesRegister(X86::EFLAGS, TRI)) {
// It is safe to remove CmpInstr if EFLAGS is updated again.
+ IsSafe = true;
break;
-
+ }
if (!Instr.readsRegister(X86::EFLAGS, TRI))
continue;
// EFLAGS is used by this instruction.
- if (SrcReg2 != 0 && Sub->getOperand(1).getReg() == SrcReg2 &&
- Sub->getOperand(2).getReg() == SrcReg) {
-
+ if (IsSwapped) {
// If we have SUB(r1, r2) and CMP(r2, r1), the condition code needs
// to be changed from r2 > r1 to r1 < r2, from r2 < r1 to r1 > r2, etc.
unsigned NewOpc = getSwappedConditionForSET(Instr.getOpcode());
// instructions will be modified.
OpsToUpdate.push_back(std::make_pair(&*I, NewOpc));
}
+ if (Instr.killsRegister(X86::EFLAGS, TRI)) {
+ IsSafe = true;
+ break;
+ }
+ }
+
+ // If EFLAGS is not killed nor re-defined, we should check whether it is
+ // live-out. If it is live-out, do not optimize.
+ if (IsSwapped && !IsSafe) {
+ MachineBasicBlock *MBB = CmpInstr->getParent();
+ for (MachineBasicBlock::succ_iterator SI = MBB->succ_begin(),
+ SE = MBB->succ_end(); SI != SE; ++SI)
+ if ((*SI)->isLiveIn(X86::EFLAGS))
+ return false;
}
// Make sure Sub instruction defines EFLAGS.