/// follow non-inbounds geps. This allows it to remain usable for icmp ult/etc.
/// folding.
static Constant *stripAndComputeConstantOffsets(const DataLayout *TD,
- Value *&V) {
+ Value *&V,
+ bool AllowNonInbounds = false) {
assert(V->getType()->getScalarType()->isPointerTy());
// Without DataLayout, just be conservative for now. Theoretically, more could
Visited.insert(V);
do {
if (GEPOperator *GEP = dyn_cast<GEPOperator>(V)) {
- if (!GEP->isInBounds() || !GEP->accumulateConstantOffset(*TD, Offset))
+ if ((!AllowNonInbounds && !GEP->isInBounds()) ||
+ !GEP->accumulateConstantOffset(*TD, Offset))
break;
V = GEP->getPointerOperand();
} else if (Operator::getOpcode(V) == Instruction::BitCast) {
return ConstantInt::get(GetCompareTy(LHS),
!CmpInst::isTrueWhenEqual(Pred));
}
+
+ // Even if an non-inbounds GEP occurs along the path we can still optimize
+ // equality comparisons concerning the result. We avoid walking the whole
+ // chain again by starting where the last calls to
+ // stripAndComputeConstantOffsets left off and accumulate the offsets.
+ Constant *LHSNoBound = stripAndComputeConstantOffsets(TD, LHS, true);
+ Constant *RHSNoBound = stripAndComputeConstantOffsets(TD, RHS, true);
+ if (LHS == RHS)
+ return ConstantExpr::getICmp(Pred,
+ ConstantExpr::getAdd(LHSOffset, LHSNoBound),
+ ConstantExpr::getAdd(RHSOffset, RHSNoBound));
}
// Otherwise, fail.
ret i1 %cmp
; CHECK-NEXT: ret i1 false
}
+
+define i1 @non_inbounds_gep_compare(i64* %a) {
+; CHECK-LABEL: @non_inbounds_gep_compare(
+; Equality compares with non-inbounds GEPs can be folded.
+ %x = getelementptr i64* %a, i64 42
+ %cmp = icmp eq i64* %a, %x
+ ret i1 %cmp
+; CHECK-NEXT: ret i1 false
+}