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Move some folding for add/sub to gtFoldExpr #128200

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Move some folding for add/sub to gtFoldExpr #128200

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92dcd3a
Move some GT_SUB simplifications from morph to gtFoldExpr
tannergooding May 14, 2026
1f91448
Move some GT_ADD simplifications from morph to gtFoldExpr
tannergooding May 14, 2026
302fada
Don't fold for T0 opts
tannergooding May 17, 2026
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82 changes: 81 additions & 1 deletion src/coreclr/jit/gentree.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -15097,12 +15097,92 @@ GenTree* Compiler::gtFoldExprBinary(GenTreeOp* tree)
return gtFoldExprSpecial(tree);
}
}
else if (tree->OperIsCompare())

genTreeOps oper = tree->OperGet();

if (GenTree::OperIsCompare(oper))
{
// comparisons of two local variables can sometimes be folded
return gtFoldExprCompare(tree);
}

if (!opts.OptimizationEnabled())
{
return tree;
}
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switch (oper)
{
case GT_ADD:
{
if (tree->gtOverflow())
{
break;
}

if (op1->OperIs(GT_NEG))
{
JITDUMP("Folding (-a) + b => b - a\n")

tree->gtOp1 = op2;
tree->gtOp2 = op1->gtGetOp1();

tree->SetOper(GT_SUB, GenTree::PRESERVE_VN);
tree->ToggleReverseOp();

return tree;
}

if (op2->OperIs(GT_NEG))
{
JITDUMP("Folding a + (-b) => a - b\n")

tree->gtOp2 = op2->gtGetOp1();
tree->SetOper(GT_SUB, GenTree::PRESERVE_VN);

return tree;
}
break;
}

case GT_SUB:
{
if (tree->gtOverflow())
{
break;
}

if (op2->OperIs(GT_NEG))
{
if (op1->OperIs(GT_NEG))
{
JITDUMP("Folding (-a) - (-b) => b - a\n")

tree->gtOp1 = op2->gtGetOp1();
tree->gtOp2 = op1->gtGetOp1();

tree->ToggleReverseOp();
return tree;
}
else
{
JITDUMP("Folding a - (-b) => a + b\n")

tree->gtOp2 = op2->gtGetOp1();
tree->SetOper(GT_ADD, GenTree::PRESERVE_VN);

return tree;
}
}
break;
}

default:
{
break;
}
}

return tree;
}

Expand Down
5 changes: 5 additions & 0 deletions src/coreclr/jit/gentree.h
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Expand Up @@ -2265,6 +2265,11 @@ struct GenTree
gtFlags &= ~GTF_REVERSE_OPS;
}

void ToggleReverseOp()
{
gtFlags ^= GTF_REVERSE_OPS;
}

#if defined(TARGET_XARCH)
void SetDontExtend()
{
Expand Down
78 changes: 0 additions & 78 deletions src/coreclr/jit/morph.cpp
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Expand Up @@ -8003,59 +8003,6 @@ GenTree* Compiler::fgMorphSmpOp(GenTree* tree, bool* optAssertionPropDone)
goto CM_ADD_OP;
}
}

// Skip optimization if non-NEG operand is constant.
// Both op1 and op2 are not constant because it was already checked above.
if (opts.OptimizationEnabled())
{
if (!op2->OperIs(GT_NEG))
{
break;
}

if (op1->OperIs(GT_NEG) && gtCanSwapOrder(op1, op2))
{
// -a - -b = > b - a
// SUB(NEG(a), NEG(b)) => SUB(b, a)

// tree: SUB
// op1: NEG
// op1Child: a
// op2: NEG
// op2Child: b

GenTree* op1Child = op1->AsOp()->gtOp1; // a
GenTree* op2Child = op2->AsOp()->gtOp1; // b
tree->AsOp()->gtOp1 = op2Child;
tree->AsOp()->gtOp2 = op1Child;

DEBUG_DESTROY_NODE(op1);
DEBUG_DESTROY_NODE(op2);

op1 = op2Child;
op2 = op1Child;
}
else
{
// a - -b = > a + b
// SUB(a, NEG(b)) => ADD(a, b)

// tree: SUB
// op1: a
// op2: NEG
// op2Child: b

GenTree* op2Child = op2->AsOp()->gtOp1; // b
oper = GT_ADD;
tree->SetOper(oper, GenTree::PRESERVE_VN);
tree->AsOp()->gtOp2 = op2Child;

DEBUG_DESTROY_NODE(op2);

op2 = op2Child;
}
}

break;

case GT_DIV:
Expand Down Expand Up @@ -10618,31 +10565,6 @@ GenTree* Compiler::fgOptimizeAddition(GenTreeOp* add)
return fgMorphTree(add);
}
}

// - a + b => b - a
// ADD(NEG(a), b) => SUB(b, a)
// Do not do this if "op2" is constant for canonicalization purposes.
if (!op2->IsIntegralConst() && gtCanSwapOrder(op1, op2))
{
add->SetOper(GT_SUB);
add->gtOp1 = op2;
add->gtOp2 = op1->AsOp()->gtGetOp1();

DEBUG_DESTROY_NODE(op1);
return add;
}
}

// a + -b = > a - b
// ADD(a, NEG(b)) => SUB(a, b)
if (!op1->OperIs(GT_NEG) && op2->OperIs(GT_NEG))
{
add->SetOper(GT_SUB);
add->gtOp2 = op2->AsOp()->gtGetOp1();

DEBUG_DESTROY_NODE(op2);

return add;
}

// Fold (~x + 1) to -x.
Expand Down
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