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[InstCombine] Don't miscompile safe increment idiom
We cleverly handle cases where computation done in one argument of a select instruction is suitable for the other operand, thus obviating the need of the select and the comparison. However, the other operand cannot have flags. This fixes PR23757. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@239115 91177308-0d34-0410-b5e6-96231b3b80d8
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@@ -292,10 +292,28 @@ static Value *SimplifyWithOpReplaced(Value *V, Value *Op, Value *RepOp,
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// If this is a binary operator, try to simplify it with the replaced op.
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if (BinaryOperator *B = dyn_cast<BinaryOperator>(I)) {
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Value *Simplified = nullptr;
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if (B->getOperand(0) == Op)
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return SimplifyBinOp(B->getOpcode(), RepOp, B->getOperand(1), DL, TLI);
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if (B->getOperand(1) == Op)
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return SimplifyBinOp(B->getOpcode(), B->getOperand(0), RepOp, DL, TLI);
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Simplified =
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SimplifyBinOp(B->getOpcode(), RepOp, B->getOperand(1), DL, TLI);
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if (!Simplified && B->getOperand(1) == Op)
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Simplified =
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SimplifyBinOp(B->getOpcode(), B->getOperand(0), RepOp, DL, TLI);
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if (Simplified) {
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// Consider:
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// %cmp = icmp eq i32 %x, 2147483647
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// %add = add nsw i32 %x, 1
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// %sel = select i1 %cmp, i32 -2147483648, i32 %add
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//
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// We can't replace %sel with %add unless we strip away the flags.
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if (isa<OverflowingBinaryOperator>(B)) {
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B->setHasNoSignedWrap(false);
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B->setHasNoUnsignedWrap(false);
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}
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if (isa<PossiblyExactOperator>(B))
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B->setIsExact(false);
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}
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return Simplified;
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}
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// Same for CmpInsts.
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