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Allow gtFoldExprSpecial to handle side effects (#103382)
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* Allow gtFoldExprSpecial to handle side effects

* Ensure that return expressions are properly treated as having side effects
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@tannergooding
tannergooding authored Jun 13, 2024
1 parent 0afabfb commit daf6cdc
Showing 1 changed file with 65 additions and 40 deletions.
105 changes: 65 additions & 40 deletions src/coreclr/jit/gentree.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -14327,15 +14327,12 @@ GenTree* Compiler::gtFoldExprSpecial(GenTree* tree)

val = cons->AsIntConCommon()->IconValue();

// Transforms that would drop op cannot be performed if op has side effects
bool opHasSideEffects = (op->gtFlags & GTF_SIDE_EFFECT) != 0;

// Helper function that creates a new IntCon node and morphs it, if required
auto NewMorphedIntConNode = [&](int value) -> GenTreeIntCon* {
GenTreeIntCon* icon = gtNewIconNode(value);
if (fgGlobalMorph)
{
fgMorphTreeDone(icon);
INDEBUG(icon->gtDebugFlags |= GTF_DEBUG_NODE_MORPHED);
}
return icon;
};
Expand Down Expand Up @@ -14370,43 +14367,52 @@ GenTree* Compiler::gtFoldExprSpecial(GenTree* tree)
switch (oper)
{
case GT_LE:
if (tree->IsUnsigned() && (val == 0) && (op1 == cons) && !opHasSideEffects)
{
if (tree->IsUnsigned() && (val == 0) && (op1 == cons))
{
// unsigned (0 <= x) is always true
op = NewMorphedIntConNode(1);
op = gtWrapWithSideEffects(NewMorphedIntConNode(1), op, GTF_ALL_EFFECT);
goto DONE_FOLD;
}
break;
}

case GT_GE:
if (tree->IsUnsigned() && (val == 0) && (op2 == cons) && !opHasSideEffects)
{
if (tree->IsUnsigned() && (val == 0) && (op2 == cons))
{
// unsigned (x >= 0) is always true
op = NewMorphedIntConNode(1);
op = gtWrapWithSideEffects(NewMorphedIntConNode(1), op, GTF_ALL_EFFECT);
goto DONE_FOLD;
}
break;
}

case GT_LT:
if (tree->IsUnsigned() && (val == 0) && (op2 == cons) && !opHasSideEffects)
{
if (tree->IsUnsigned() && (val == 0) && (op2 == cons))
{
// unsigned (x < 0) is always false
op = NewMorphedIntConNode(0);
op = gtWrapWithSideEffects(NewMorphedIntConNode(0), op, GTF_ALL_EFFECT);
goto DONE_FOLD;
}
break;
}

case GT_GT:
if (tree->IsUnsigned() && (val == 0) && (op1 == cons) && !opHasSideEffects)
{
if (tree->IsUnsigned() && (val == 0) && (op1 == cons))
{
// unsigned (0 > x) is always false
op = NewMorphedIntConNode(0);
op = gtWrapWithSideEffects(NewMorphedIntConNode(0), op, GTF_ALL_EFFECT);
goto DONE_FOLD;
}
}
FALLTHROUGH;

case GT_EQ:
case GT_NE:

{
// Optimize boxed value classes; these are always false. This IL is
// generated when a generic value is tested against null:
// <T> ... foo(T x) { ... if ((object)x == null) ...
Expand Down Expand Up @@ -14468,57 +14474,59 @@ GenTree* Compiler::gtFoldExprSpecial(GenTree* tree)
{
return gtFoldBoxNullable(tree);
}

break;
}

case GT_ADD:
{
if (val == 0)
{
goto DONE_FOLD;
}
break;
}

case GT_MUL:
{
if (val == 1)
{
goto DONE_FOLD;
}
else if (val == 0)
{
/* Multiply by zero - return the 'zero' node, but not if side effects */
if (!opHasSideEffects)
{
op = cons;
goto DONE_FOLD;
}
// Multiply by zero - return the 'zero' node
op = gtWrapWithSideEffects(cons, op, GTF_ALL_EFFECT);
goto DONE_FOLD;
}
break;
}

case GT_DIV:
case GT_UDIV:
{
if ((op2 == cons) && (val == 1) && !op1->OperIsConst())
{
goto DONE_FOLD;
}
break;
}

case GT_SUB:
{
if ((op2 == cons) && (val == 0) && !op1->OperIsConst())
{
goto DONE_FOLD;
}
break;
}

case GT_AND:
{
if (val == 0)
{
/* AND with zero - return the 'zero' node, but not if side effects */

if (!opHasSideEffects)
{
op = cons;
goto DONE_FOLD;
}
// AND with zero - return the 'zero' node
op = gtWrapWithSideEffects(cons, op, GTF_ALL_EFFECT);
goto DONE_FOLD;
}
else if (val == 0xFF)
{
Expand Down Expand Up @@ -14551,8 +14559,10 @@ GenTree* Compiler::gtFoldExprSpecial(GenTree* tree)
}
}
break;
}

case GT_OR:
{
if (val == 0)
{
goto DONE_FOLD;
Expand All @@ -14563,34 +14573,33 @@ GenTree* Compiler::gtFoldExprSpecial(GenTree* tree)

assert(val == 1);

/* OR with one - return the 'one' node, but not if side effects */

if (!opHasSideEffects)
{
op = cons;
goto DONE_FOLD;
}
// OR with one - return the 'one' node
op = gtWrapWithSideEffects(cons, op, GTF_ALL_EFFECT);
goto DONE_FOLD;
}
break;
}

case GT_LSH:
case GT_RSH:
case GT_RSZ:
case GT_ROL:
case GT_ROR:
{
if (val == 0)
{
if (op2 == cons)
{
goto DONE_FOLD;
}
else if (!opHasSideEffects)
else
{
op = cons;
op = gtWrapWithSideEffects(cons, op, GTF_ALL_EFFECT);
goto DONE_FOLD;
}
}
break;
}

case GT_QMARK:
{
Expand All @@ -14613,9 +14622,8 @@ GenTree* Compiler::gtFoldExprSpecial(GenTree* tree)
{
fgWalkTreePre(&op, gtClearColonCond);
}
}

goto DONE_FOLD;
}

default:
break;
Expand All @@ -14632,6 +14640,13 @@ GenTree* Compiler::gtFoldExprSpecial(GenTree* tree)
JITDUMP("Transformed into:\n");
DISPTREE(op);

if (fgGlobalMorph)
{
// We can sometimes produce a comma over the constant if the original op
// had a side effect, so just ensure we set the flag (which will be already
// set for the operands otherwise).
INDEBUG(op->gtDebugFlags |= GTF_DEBUG_NODE_MORPHED);
}
return op;
}

Expand Down Expand Up @@ -16903,9 +16918,19 @@ bool Compiler::gtNodeHasSideEffects(GenTree* tree, GenTreeFlags flags)
// Are there only GTF_CALL side effects remaining? (and no other side effect kinds)
if (flags & GTF_CALL)
{
if (tree->OperGet() == GT_CALL)
GenTree* potentialCall = tree;

if (potentialCall->OperIs(GT_RET_EXPR))
{
// We need to preserve return expressions where the underlying call
// has side effects. Otherwise early folding can result in us dropping
// the call.
potentialCall = potentialCall->AsRetExpr()->gtInlineCandidate;
}

if (potentialCall->OperIs(GT_CALL))
{
GenTreeCall* const call = tree->AsCall();
GenTreeCall* const call = potentialCall->AsCall();
const bool ignoreExceptions = (flags & GTF_EXCEPT) == 0;
const bool ignoreCctors = (flags & GTF_IS_IN_CSE) != 0; // We can CSE helpers that run cctors.
if (!call->HasSideEffects(this, ignoreExceptions, ignoreCctors))
Expand Down

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