InstSimplify: Fold equality comparisons between non-inbounds GEPs.
Overflow doesn't affect the correctness of equalities. Computing this is cheap,
we just reuse the computation for the inbounds case and try to peel of more
non-inbounds GEPs. This pattern is unlikely to ever appear in code generated by
Clang, but SCEV occasionally produces it.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@191200 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Analysis/InstructionSimplify.cpp b/lib/Analysis/InstructionSimplify.cpp
index 4b29824..af65cb7 100644
--- a/lib/Analysis/InstructionSimplify.cpp
+++ b/lib/Analysis/InstructionSimplify.cpp
@@ -668,7 +668,8 @@
/// 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
@@ -685,7 +686,8 @@
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) {
@@ -1837,6 +1839,17 @@
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.