JIT: Optimize bit-wise AND with a constant mask in combination with a left shift in a compare #111979
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…a left shift in a compare This optmizes the generated code when having a pattern like '(SomeConstant & (1 << value)) != 0' which was previously only optimized for '(variable & (1 << value)) != 0'. Fix dotnet#111554
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Tagging subscribers to this area: @JulieLeeMSFT, @jakobbotsch |
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jakobbotsch
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Jan 30, 2025
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| GenTree* lshRight = cmp->gtGetOp2(); | ||
| GenTree* lshLeft = cmp->gtGetOp1(); | ||
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| if (lsh->OperIs(GT_LSH) && varTypeIsIntOrI(lsh->TypeGet()) && lsh->gtGetOp1()->IsIntegralConst(1)) | ||
| if (lshRight->OperIs(GT_LSH) && varTypeIsIntOrI(lshRight->TypeGet()) && lshRight->gtGetOp1()->IsIntegralConst(1)) | ||
| { | ||
| cmp->SetOper(cmp->OperIs(GT_TEST_EQ) ? GT_BITTEST_EQ : GT_BITTEST_NE); | ||
| cmp->AsOp()->gtOp2 = lsh->gtGetOp2(); | ||
| cmp->AsOp()->gtOp2 = lshRight->gtGetOp2(); | ||
| cmp->gtGetOp2()->ClearContained(); | ||
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| BlockRange().Remove(lsh->gtGetOp1()); | ||
| BlockRange().Remove(lsh); | ||
| BlockRange().Remove(lshRight->gtGetOp1()); | ||
| BlockRange().Remove(lshRight); | ||
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| return cmp->gtNext; | ||
| } | ||
| else if (lshLeft->OperIs(GT_LSH) && varTypeIsIntOrI(lshLeft->TypeGet()) && lshLeft->gtGetOp1()->IsIntegralConst(1)) | ||
| { | ||
| cmp->SetOper(cmp->OperIs(GT_TEST_EQ) ? GT_BITTEST_EQ : GT_BITTEST_NE); | ||
| cmp->AsOp()->gtOp1 = cmp->AsOp()->gtOp2; | ||
| cmp->AsOp()->gtOp2 = lshLeft->gtGetOp2(); | ||
| cmp->gtGetOp2()->ClearContained(); | ||
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| BlockRange().Remove(lshLeft->gtGetOp1()); | ||
| BlockRange().Remove(lshLeft); |
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Can the duplication be avoided?
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I could minimize it using a helper method. Can I just put the method in lower.h with the body in the header like ReplaceWithLclVar or differently?
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I would suggest maybe just doing something like:
GenTree** lsh = &cmp->AsOp()->gtOp1;
GenTree** op = &cmp->AsOp()->gtOp2;
if (!(*lsh)->OperIs(GT_LSH))
std::swap(lsh, op);
if ((*lsh)->OperIs(GT_LSH) && varTypeIsIntOrI(*lsh) && (*lsh)->gtGetOp1()->IsIntegralConst(1))
{
cmp->SetOper(cmp->OperIs(GT_TEST_EQ) ? GT_BITTEST_EQ : GT_BITTEST_NE);
*lsh = (*lsh)->gtGetOp2();
...
}
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This resolves #111554.
C# code (example code from the issue):
x64 (before):
x64 (after):