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Do not eliminate casts from FP types when optimizing narrow stores #53667

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kunalspathak merged 1 commit into from
Jul 13, 2021
Merged

Do not eliminate casts from FP types when optimizing narrow stores #53667

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Do not eliminate casts from FP types 
An optimization in morph was deleting casts
on the RHS of a narrow store if the cast-to-type
was wider than the type being stored. This is only
valid for casts from integral types, as the backend
does not handle "STOREIND(byte*, double)", nor is there
an instruction to go from an XMM register to a narrow
memory location on x86/x64.

The issue is not reproducible right now because
fgMorphCast wraps the casts in question, but it is
an invalid IR transformation nonetheless, and similar
code in fgMorphSmpOpOptional guards against non-integral sources.
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@SingleAccretion
SingleAccretion committed Jun 7, 2021
commit 94de26a3d610b5c8499f102205bdc39c67f2d624
9 changes: 5 additions & 4 deletions src/coreclr/jit/morph.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -13378,18 +13378,19 @@ GenTree* Compiler::fgMorphSmpOp(GenTree* tree, MorphAddrContext* mac)
tree->AsOp()->gtOp1 = op1;
}

/* If we are storing a small type, we might be able to omit a cast */
if ((effectiveOp1->gtOper == GT_IND) && varTypeIsSmall(effectiveOp1->TypeGet()))
// If we are storing a small type, we might be able to omit a cast.
if (effectiveOp1->OperIs(GT_IND) && varTypeIsSmall(effectiveOp1))
{
if (!gtIsActiveCSE_Candidate(op2) && (op2->gtOper == GT_CAST) && !op2->gtOverflow())
if (!gtIsActiveCSE_Candidate(op2) && op2->OperIs(GT_CAST) &&
varTypeIsIntegral(op2->AsCast()->CastOp()) && !op2->gtOverflow())
{
var_types castType = op2->CastToType();

// If we are performing a narrowing cast and
// castType is larger or the same as op1's type
// then we can discard the cast.

if (varTypeIsSmall(castType) && (genTypeSize(castType) >= genTypeSize(effectiveOp1->TypeGet())))
if (varTypeIsSmall(castType) && (genTypeSize(castType) >= genTypeSize(effectiveOp1)))
{
tree->AsOp()->gtOp2 = op2 = op2->AsCast()->CastOp();
}
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