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JIT: Avoid creating impossible equality assertions #118586

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Aug 11, 2025
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JIT: Avoid creating impossible equality assertions #118586

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13 changes: 11 additions & 2 deletions src/coreclr/jit/assertionprop.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1232,9 +1232,18 @@ AssertionIndex Compiler::optCreateAssertion(GenTree* op1, GenTree* op2, optAsser
if (op2->OperIs(GT_CNS_INT))
{
ssize_t iconVal = op2->AsIntCon()->IconValue();
if (varTypeIsSmall(lclVar) && op1->OperIs(GT_STORE_LCL_VAR))
if (varTypeIsSmall(lclVar))
{
iconVal = optCastConstantSmall(iconVal, lclVar->TypeGet());
ssize_t truncatedIconVal = optCastConstantSmall(iconVal, lclVar->TypeGet());
if (!op1->OperIs(GT_STORE_LCL_VAR) && (truncatedIconVal != iconVal))
{
// This assertion would be saying that a small local is equal to a value
// outside its range. It means this block is unreachable. Avoid creating
// such impossible assertions which can hit assertions in other places.
goto DONE_ASSERTION;
}

iconVal = truncatedIconVal;
if (!optLocalAssertionProp)
{
assertion.op2.vn = vnStore->VNForIntCon(static_cast<int>(iconVal));
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