forked from OSchip/llvm-project
[InstCombine] Don't miscompile select to poison
If we have (select a, b, c), it is sometimes valid to simplify this to a single select operand. However, doing so is only valid if the computation doesn't inject poison into the computation. It might be helpful to consider the following example: (select (icmp ne %i, INT_MAX), (add nsw %i, 1), INT_MIN) The select is equivalent to (add %i, 1) but not (add nsw %i, 1). Self hosting on x86_64 revealed that this occurs very, very rarely so bailing out is hopefully pretty reasonable. llvm-svn: 239215
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llvm
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@ -292,6 +292,19 @@ 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 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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if (BinaryOperator *B = dyn_cast<BinaryOperator>(I)) {
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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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if (B->hasNoSignedWrap() || B->hasNoUnsignedWrap())
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return nullptr;
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if (isa<PossiblyExactOperator>(B))
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if (B->isExact())
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return nullptr;
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if (B->getOperand(0) == Op)
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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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return SimplifyBinOp(B->getOpcode(), RepOp, B->getOperand(1), DL, TLI);
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if (B->getOperand(1) == Op)
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if (B->getOperand(1) == Op)
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@ -1532,3 +1532,16 @@ define i32 @test_max_of_min(i32 %a) {
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%s1 = select i1 %c1, i32 %s0, i32 -1
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%s1 = select i1 %c1, i32 %s0, i32 -1
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ret i32 %s1
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ret i32 %s1
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}
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}
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define i32 @PR23757(i32 %x) {
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; CHECK-LABEL: @PR23757
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; CHECK: %[[cmp:.*]] = icmp eq i32 %x, 2147483647
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; CHECK-NEXT: %[[add:.*]] = add nsw i32 %x, 1
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; CHECK-NEXT: %[[sel:.*]] = select i1 %[[cmp]], i32 -2147483648, i32 %[[add]]
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; CHECK-NEXT: ret i32 %[[sel]]
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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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ret i32 %sel
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}
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