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Improve morphing of bit comparisons to constant 0/1 #73120

Merged
merged 12 commits into from
Sep 6, 2022
Merged

Improve morphing of bit comparisons to constant 0/1 #73120

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9e9f6d4
Morph `(x >> y & 1) NE/EQ 0/1` into `(x & (1 << y)) NE/EQ 0`
dubiousconst282 Jul 31, 2022
b777d6f
Fix cond reversing
dubiousconst282 Jul 31, 2022
2994226
Transform TEST_NE(x, 1) into AND(x, 1)
dubiousconst282 Jul 31, 2022
256eb9f
Recalculate containment when changing TEST to AND
dubiousconst282 Jul 31, 2022
28985b7
Fix formatting
dubiousconst282 Jul 31, 2022
fcf122f
Update node flags when changing operands
dubiousconst282 Aug 1, 2022
8072f4d
Check heuristic before morphing
dubiousconst282 Aug 1, 2022
8504793
Revert TEST_NE -> AND, do it earlier and check for LSH
dubiousconst282 Aug 2, 2022
f366510
Use SetAllEffectsFlags() instead of manual bit ops
dubiousconst282 Aug 2, 2022
991ff69
Fix formatting
dubiousconst282 Aug 2, 2022
7fef935
Remove unnecessary check
dubiousconst282 Aug 3, 2022
5a0585a
Merge branch 'main' into bt-shift-morph
dubiousconst282 Aug 27, 2022
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47 changes: 21 additions & 26 deletions src/coreclr/jit/lower.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -2850,38 +2850,33 @@ GenTree* Lowering::OptimizeConstCompare(GenTree* cmp)
GenTree* andOp1 = op1->gtGetOp1();
GenTree* andOp2 = op1->gtGetOp2();

if (op2Value != 0)
//
// If we don't have a 0 compare we can get one by transforming ((x AND mask) EQ|NE mask)
// into ((x AND mask) NE|EQ 0) when mask is a single bit.
//
if ((op2Value != 0) && isPow2(static_cast<target_size_t>(op2Value)) && andOp2->IsIntegralConst(op2Value))
{
op2Value = 0;
op2->SetIconValue(0);
cmp->SetOperRaw(GenTree::ReverseRelop(cmp->OperGet()));
}

// Transform ((x AND 1) NE 0) into (x AND 1)
// The compiler requires jumps to have relop operands, so we do not fold that case.
if ((op2Value == 0) && cmp->OperIs(GT_NE) && andOp2->IsIntegralConst(1))
{
// Optimizes (X & 1) == 1 to (X & 1)
// The compiler requires jumps to have relop operands, so we do not fold that case.
LIR::Use cmpUse;
if ((op2Value == 1) && cmp->OperIs(GT_EQ))
if ((genActualType(op1) == cmp->TypeGet()) && BlockRange().TryGetUse(cmp, &cmpUse) &&
!cmpUse.User()->OperIs(GT_JTRUE) && !cmpUse.User()->OperIsConditional())
{
if (andOp2->IsIntegralConst(1) && (genActualType(op1) == cmp->TypeGet()) &&
BlockRange().TryGetUse(cmp, &cmpUse) && !cmpUse.User()->OperIs(GT_JTRUE) &&
!cmpUse.User()->OperIsConditional())
{
GenTree* next = cmp->gtNext;
GenTree* next = cmp->gtNext;

cmpUse.ReplaceWith(op1);
cmpUse.ReplaceWith(op1);

BlockRange().Remove(cmp->gtGetOp2());
BlockRange().Remove(cmp);

return next;
}
}

//
// If we don't have a 0 compare we can get one by transforming ((x AND mask) EQ|NE mask)
// into ((x AND mask) NE|EQ 0) when mask is a single bit.
//
BlockRange().Remove(cmp->gtGetOp2());
BlockRange().Remove(cmp);

if (isPow2<target_size_t>(static_cast<target_size_t>(op2Value)) && andOp2->IsIntegralConst(op2Value))
{
op2Value = 0;
op2->SetIconValue(0);
cmp->SetOperRaw(GenTree::ReverseRelop(cmp->OperGet()));
return next;
}
}

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83 changes: 45 additions & 38 deletions src/coreclr/jit/morph.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -11978,77 +11978,84 @@ GenTree* Compiler::fgOptimizeEqualityComparisonWithConst(GenTreeOp* cmp)
//
// Now we check for a compare with the result of an '&' operator
//
// Here we look for the following transformation:
// Here we look for the following transformation (canonicalization):
//
// EQ/NE EQ/NE
// / \ / \.
// AND CNS 0/1 -> AND CNS 0
// / \ / \.
// RSZ/RSH CNS 1 x CNS (1 << y)
// / \.
// x CNS_INT +y
// RSZ/RSH CNS 1 x LSH (folded if 'y' is constant)
// / \ / \.
// x y 1 y

if (fgGlobalMorph && op1->OperIs(GT_AND) && op1->AsOp()->gtGetOp1()->OperIs(GT_RSZ, GT_RSH))
{
GenTreeOp* andOp = op1->AsOp();
GenTreeOp* rshiftOp = andOp->gtGetOp1()->AsOp();

if (!rshiftOp->gtGetOp2()->IsCnsIntOrI())
{
goto SKIP;
}

ssize_t shiftAmount = rshiftOp->gtGetOp2()->AsIntCon()->IconValue();

if (shiftAmount < 0)
{
goto SKIP;
}

if (!andOp->gtGetOp2()->IsIntegralConst(1))
{
goto SKIP;
}

GenTreeIntConCommon* andMask = andOp->gtGetOp2()->AsIntConCommon();

if (andOp->TypeIs(TYP_INT))
// If the shift is constant, we can fold the mask and delete the shift node:
// -> AND(x, CNS(1 << y)) EQ/NE 0
if (rshiftOp->gtGetOp2()->IsCnsIntOrI())
{
if (shiftAmount > 31)
ssize_t shiftAmount = rshiftOp->gtGetOp2()->AsIntCon()->IconValue();

if (shiftAmount < 0)
{
goto SKIP;
}

andMask->SetIconValue(static_cast<int32_t>(1 << shiftAmount));
GenTreeIntConCommon* andMask = andOp->gtGetOp2()->AsIntConCommon();

// Reverse the condition if necessary.
if (op2Value == 1)
if (andOp->TypeIs(TYP_INT) && shiftAmount < 32)
{
andMask->SetIconValue(static_cast<int32_t>(1 << shiftAmount));
}
else if (andOp->TypeIs(TYP_LONG) && shiftAmount < 64)
{
gtReverseCond(cmp);
op2->SetIconValue(0);
andMask->SetLngValue(1LL << shiftAmount);
}
else
{
goto SKIP; // Unsupported type or invalid shift amount.
}
andOp->gtOp1 = rshiftOp->gtGetOp1();

DEBUG_DESTROY_NODE(rshiftOp->gtGetOp2());
DEBUG_DESTROY_NODE(rshiftOp);
}
else if (andOp->TypeIs(TYP_LONG))
// Otherwise, if the shift is not constant, just rewire the nodes and reverse the shift op:
// AND(RSH(x, y), 1) -> AND(x, LSH(1, y))
//
// On ARM/BMI2 the original pattern should result in smaller code when comparing to non-zero,
// the other case where this transform is worth is if the compare is being used by a jump.
//
else
{
if (shiftAmount > 63)
if (!(cmp->gtFlags & GTF_RELOP_JMP_USED) &&
((op2Value == 0 && cmp->OperIs(GT_NE)) || (op2Value == 1 && cmp->OperIs(GT_EQ))))
{
goto SKIP;
}

andMask->SetLngValue(1ll << shiftAmount);
andOp->gtOp1 = rshiftOp->gtGetOp1();
rshiftOp->gtOp1 = andOp->gtGetOp2();
andOp->gtOp2 = rshiftOp;

// Reverse the cond if necessary
if (op2Value == 1)
{
gtReverseCond(cmp);
op2->SetLngValue(0);
}
rshiftOp->SetAllEffectsFlags(rshiftOp->gtGetOp1(), rshiftOp->gtGetOp2());
rshiftOp->SetOper(GT_LSH);
}

andOp->gtOp1 = rshiftOp->gtGetOp1();

DEBUG_DESTROY_NODE(rshiftOp->gtGetOp2());
DEBUG_DESTROY_NODE(rshiftOp);
// Reverse the condition if necessary.
if (op2Value == 1)
{
gtReverseCond(cmp);
op2->SetIntegralValue(0);
}
}
}

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