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InstCombine: Don't fold (X <<s log(INT_MIN)) /s INT_MIN to X
Consider the case where X is 2. (2 <<s 31)/s-2147483648 is zero but we would fold to X. Note that this is valid when we are in the unsigned domain because we require NUW: 2 <<u 31 results in poison. This fixes PR21245. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@219568 91177308-0d34-0410-b5e6-96231b3b80d8
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@ -762,7 +762,8 @@ Instruction *InstCombiner::commonIDivTransforms(BinaryOperator &I) {
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}
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}
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if ((IsSigned && match(LHS, m_NSWShl(m_Value(X), m_APInt(C1)))) ||
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if ((IsSigned && match(LHS, m_NSWShl(m_Value(X), m_APInt(C1))) &&
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*C1 != C1->getBitWidth() - 1) ||
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(!IsSigned && match(LHS, m_NUWShl(m_Value(X), m_APInt(C1))))) {
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APInt Quotient(C1->getBitWidth(), /*Val=*/0ULL, IsSigned);
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APInt C1Shifted = APInt::getOneBitSet(
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@ -247,3 +247,20 @@ define i32 @test28(i32 %a) {
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; CHECK-NEXT: %div = mul nuw i32 %a, 12
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; CHECK-NEXT: ret i32 %div
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}
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define i32 @test29(i32 %a) {
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%mul = shl nsw i32 %a, 31
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%div = sdiv i32 %mul, -2147483648
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ret i32 %div
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; CHECK-LABEL: @test29(
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; CHECK-NEXT: %[[and:.*]] = and i32 %a, 1
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; CHECK-NEXT: ret i32 %[[and]]
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}
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define i32 @test30(i32 %a) {
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%mul = shl nuw i32 %a, 31
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%div = udiv i32 %mul, -2147483648
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ret i32 %div
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; CHECK-LABEL: @test30(
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; CHECK-NEXT: ret i32 %a
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}
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