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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
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@ -668,7 +668,8 @@ Value *llvm::SimplifyAddInst(Value *Op0, Value *Op1, bool isNSW, bool isNUW,
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/// follow non-inbounds geps. This allows it to remain usable for icmp ult/etc.
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/// folding.
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static Constant *stripAndComputeConstantOffsets(const DataLayout *TD,
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Value *&V) {
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Value *&V,
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bool AllowNonInbounds = false) {
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assert(V->getType()->getScalarType()->isPointerTy());
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// Without DataLayout, just be conservative for now. Theoretically, more could
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@ -685,7 +686,8 @@ static Constant *stripAndComputeConstantOffsets(const DataLayout *TD,
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Visited.insert(V);
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do {
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if (GEPOperator *GEP = dyn_cast<GEPOperator>(V)) {
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if (!GEP->isInBounds() || !GEP->accumulateConstantOffset(*TD, Offset))
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if ((!AllowNonInbounds && !GEP->isInBounds()) ||
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!GEP->accumulateConstantOffset(*TD, Offset))
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break;
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V = GEP->getPointerOperand();
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} else if (Operator::getOpcode(V) == Instruction::BitCast) {
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@ -1837,6 +1839,17 @@ static Constant *computePointerICmp(const DataLayout *TD,
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return ConstantInt::get(GetCompareTy(LHS),
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!CmpInst::isTrueWhenEqual(Pred));
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}
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// Even if an non-inbounds GEP occurs along the path we can still optimize
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// equality comparisons concerning the result. We avoid walking the whole
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// chain again by starting where the last calls to
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// stripAndComputeConstantOffsets left off and accumulate the offsets.
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Constant *LHSNoBound = stripAndComputeConstantOffsets(TD, LHS, true);
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Constant *RHSNoBound = stripAndComputeConstantOffsets(TD, RHS, true);
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if (LHS == RHS)
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return ConstantExpr::getICmp(Pred,
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ConstantExpr::getAdd(LHSOffset, LHSNoBound),
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ConstantExpr::getAdd(RHSOffset, RHSNoBound));
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}
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// Otherwise, fail.
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@ -717,3 +717,12 @@ define i1 @alloca_gep(i64 %a, i64 %b) {
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ret i1 %cmp
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; CHECK-NEXT: ret i1 false
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}
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define i1 @non_inbounds_gep_compare(i64* %a) {
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; CHECK-LABEL: @non_inbounds_gep_compare(
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; Equality compares with non-inbounds GEPs can be folded.
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%x = getelementptr i64* %a, i64 42
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%cmp = icmp eq i64* %a, %x
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ret i1 %cmp
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; CHECK-NEXT: ret i1 false
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}
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