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JIT: Optimize bit-wise AND with a constant mask in combination with a left shift in a compare #111979

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Feb 4, 2025
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JIT: Optimize bit-wise AND with a constant mask in combination with a left shift in a compare #111979

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f9bdee6
JIT: Optimize bit-wise AND with a constant mask in combination with …
varelen Jan 29, 2025
31c3ac3
JIT: Minimize code duplicate when lowering left shift with const
varelen Jan 31, 2025
f1d8d60
JIT: Include test/eq with operands switched containing left shift in …
varelen Jan 31, 2025
5783c3c
JIT: Improve code for optimizing test/eq with a left shift op
varelen Jan 31, 2025
3dd15ef
Merge branch 'main' into jit-use-bt-instruction-for-constant-mask-iss…
varelen Jan 31, 2025
9cf8b1b
Merge branch 'main' into jit-use-bt-instruction-for-constant-mask-iss…
varelen Feb 1, 2025
e189bb5
Merge branch 'main' into jit-use-bt-instruction-for-constant-mask-iss…
varelen Feb 3, 2025
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18 changes: 13 additions & 5 deletions src/coreclr/jit/lower.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -4352,24 +4352,32 @@ GenTree* Lowering::OptimizeConstCompare(GenTree* cmp)
if (cmp->OperIs(GT_TEST_EQ, GT_TEST_NE))
{
//
// Transform TEST_EQ|NE(x, LSH(1, y)) into BT(x, y) when possible. Using BT
// Transform TEST_EQ|NE(x, LSH(1, y)) or TEST_EQ|NE(LSH(1, y), x) into BT(x, y) when possible. Using BT
// results in smaller and faster code. It also doesn't have special register
// requirements, unlike LSH that requires the shift count to be in ECX.
// Note that BT has the same behavior as LSH when the bit index exceeds the
// operand bit size - it uses (bit_index MOD bit_size).
//

GenTree* lsh = cmp->gtGetOp2();
GenTree* lsh = cmp->AsOp()->gtOp1;
GenTree* op = cmp->AsOp()->gtOp2;

if (lsh->OperIs(GT_LSH) && varTypeIsIntOrI(lsh->TypeGet()) && lsh->gtGetOp1()->IsIntegralConst(1))
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);
cmp->AsOp()->gtOp2 = lsh->gtGetOp2();
cmp->gtGetOp2()->ClearContained();

BlockRange().Remove(lsh->gtGetOp1());
BlockRange().Remove(lsh);

cmp->AsOp()->gtOp1 = op;
cmp->AsOp()->gtOp2 = lsh->gtGetOp2();
cmp->gtGetOp2()->ClearContained();

return cmp->gtNext;
}
}
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