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[RyuJit Wasm] fix off by one error for br_table #123565

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[RyuJit Wasm] fix off by one error for br_table #123565

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[RyuJit Wasm] fix off by one error for br_table
AndyAyersMS Jan 23, 2026
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AndyAyersMS Jan 24, 2026
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8 changes: 7 additions & 1 deletion src/coreclr/jit/codegenwasm.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -566,8 +566,14 @@ void CodeGen::genTableBasedSwitch(GenTree* treeNode)
assert(caseCount > 0);
assert(desc->HasDefaultCase());

GetEmitter()->emitIns_I(INS_br_table, EA_4BYTE, caseCount);
// br_table list (labelidx*) labelidx
// list is prefixed with length, which is caseCount - 1
//
GetEmitter()->emitIns_I(INS_br_table, EA_4BYTE, caseCount - 1);

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@adamperlin adamperlin Jan 23, 2026

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Can you potentially add a comment here explaining that this loop will handle emitting all the targets, including the default, even though in the above count we excluded it because of Wasm's convention? We could also consider pulling emitting the default out of the loop just to be extra clear here, though I know we also have the assert above to ensure we do have a default case.

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@AndyAyersMS AndyAyersMS Jan 24, 2026

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Yes. Take another look.

// Emit the list case targets, then default case target
// (which is always the last case in the desc).
//
for (unsigned caseNum = 0; caseNum < caseCount; caseNum++)
{
BasicBlock* const caseTarget = desc->GetCase(caseNum)->getDestinationBlock();
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