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JIT: Do not remove type changing casts in lowering optimization #118636

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Merged
jakobbotsch merged 1 commit into from
Aug 13, 2025
Merged

JIT: Do not remove type changing casts in lowering optimization #118636

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11 changes: 6 additions & 5 deletions src/coreclr/jit/lower.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -5316,11 +5316,12 @@ void Lowering::LowerFieldListToFieldListOfRegisters(GenTreeFieldList* fieldLis
if ((i == numRegs - 1) && varTypeUsesIntReg(regType))
{
GenTree* node = regEntry->GetNode();
// If this is a cast that affects only bits after the return size
// then it can be removed. Those bits are undefined in all our ABIs
// for structs.
while (node->OperIs(GT_CAST) && !node->gtOverflow() && varTypeUsesIntReg(node->CastToType()) &&
varTypeUsesIntReg(node->CastFromType()) && (genTypeSize(regType) <= genTypeSize(node->CastToType())))
// If this is a truncation that affects only bits after the return
// size then it can be removed. Those bits are undefined in all our
// ABIs for structs.
while (node->OperIs(GT_CAST) && !node->gtOverflow() && (genActualType(node->CastFromType()) == TYP_INT) &&
(genActualType(node->CastToType()) == TYP_INT) &&
(genTypeSize(regType) <= genTypeSize(node->CastToType())))
{
GenTree* op = node->AsCast()->CastOp();
regEntry->SetNode(op);
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