JIT: Only optimize out integral casts for returned fields (#118593)

jakobbotsch · web-flow · commit f30c40e179a6 · 2025-08-11T22:39:38.000+02:00
diff --git a/src/coreclr/jit/lower.cpp b/src/coreclr/jit/lower.cpp
@@ -5320,7 +5320,7 @@ void Lowering::LowerFieldListToFieldListOfRegisters(GenTreeFieldList*   fieldLis
             // 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()) &&
-                   (genTypeSize(regType) <= genTypeSize(node->CastToType())))
+                   varTypeUsesIntReg(node->CastFromType()) && (genTypeSize(regType) <= genTypeSize(node->CastToType())))
             {
                 GenTree* op = node->AsCast()->CastOp();
                 regEntry->SetNode(op);

Original file line number	Diff line number	Diff line change
`@@ -5320,7 +5320,7 @@ void Lowering::LowerFieldListToFieldListOfRegisters(GenTreeFieldList* fieldLis`
`5320`	`5320`	`// then it can be removed. Those bits are undefined in all our ABIs`
`5321`	`5321`	`// for structs.`
`5322`	`5322`	`while (node->OperIs(GT_CAST) && !node->gtOverflow() && varTypeUsesIntReg(node->CastToType()) &&`
`5323`		`- (genTypeSize(regType) <= genTypeSize(node->CastToType())))`
	`5323`	`+ varTypeUsesIntReg(node->CastFromType()) && (genTypeSize(regType) <= genTypeSize(node->CastToType())))`
`5324`	`5324`	`{`
`5325`	`5325`	`GenTree* op = node->AsCast()->CastOp();`
`5326`	`5326`	`regEntry->SetNode(op);`