================
@@ -54,9 +54,34 @@ const MachineBasicBlock
*MachineSSAContext::getDefBlock(Register value) const {
return F->getRegInfo().getVRegDef(value)->getParent();
}
+static bool isUndef(const MachineInstr &MI) {
+ return MI.getOpcode() == TargetOpcode::G_IMPLICIT_DEF ||
+ MI.getOpcode() == TargetOpcode::IMPLICIT_DEF;
+}
+
+/// MachineInstr equivalent of PHINode::hasConstantOrUndefValue() for G_PHI.
template <>
bool MachineSSAContext::isConstantOrUndefValuePhi(const MachineInstr &Phi) {
- return Phi.isConstantValuePHI();
+ if (!Phi.isPHI())
+ return false;
+
+ // In later passes PHI may appear with an undef operand, getVRegDef can fail.
+ if (Phi.getOpcode() == TargetOpcode::PHI)
+ return Phi.isConstantValuePHI();
+
+ // For G_PHI we do equivalent of PHINode::hasConstantOrUndefValue().
+ const MachineRegisterInfo &MRI = Phi.getMF()->getRegInfo();
+ Register This = Phi.getOperand(0).getReg();
+ Register ConstantValue;
+ for (unsigned i = 1, e = Phi.getNumOperands(); i < e; i += 2) {
+ Register Incoming = Phi.getOperand(i).getReg();
+ if (Incoming != This && !isUndef(*MRI.getVRegDef(Incoming))) {
+ if (ConstantValue && ConstantValue != Incoming)
+ return false;
+ ConstantValue = Incoming;
+ }
+ }
----------------
nhaehnle wrote:
I don't understand this logic. Why are you looking at operand 0? What's the
meaning of `This` vs. `ConstantValue`? This looks very fishy.
https://github.com/llvm/llvm-project/pull/112866
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