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[Wasm RyuJit] Slightly smaller code for switches #122198

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Merged
AndyAyersMS merged 2 commits into from
Dec 9, 2025
Merged

[Wasm RyuJit] Slightly smaller code for switches #122198

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[Wasm RyuJit] Slightly better code for switches
AndyAyersMS Dec 4, 2025
b0a5843
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AndyAyersMS Dec 4, 2025
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10 changes: 3 additions & 7 deletions src/coreclr/jit/codegenwasm.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -328,14 +328,10 @@ void CodeGen::genTableBasedSwitch(GenTree* treeNode)
BBswtDesc* const desc = block->GetSwitchTargets();
unsigned const caseCount = desc->GetCaseCount();

// TODO-WASM: update lowering not to peel off the default
// We don't expect degenerate or default-less switches
//
assert(!desc->HasDefaultCase());

if (caseCount == 0)
{
return;
}
assert(caseCount > 0);
assert(desc->HasDefaultCase());

GetEmitter()->emitIns_I(INS_br_table, EA_4BYTE, caseCount);

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4 changes: 4 additions & 0 deletions src/coreclr/jit/fgopt.cpp
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Expand Up @@ -1657,7 +1657,11 @@ bool Compiler::fgOptimizeSwitchBranches(BasicBlock* block)
blockRange = &LIR::AsRange(block);
switchTree = blockRange->LastNode();

#ifdef TARGET_WASM
assert(switchTree->OperIs(GT_SWITCH));
#else
assert(switchTree->OperIs(GT_SWITCH_TABLE));
#endif
}
else
{
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10 changes: 3 additions & 7 deletions src/coreclr/jit/fgwasm.cpp
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Expand Up @@ -1144,7 +1144,6 @@ PhaseStatus Compiler::fgWasmControlFlow()
}

// Branch to next needs no block, unless this is a switch
// (eventually when we leave the default on the switch we can remove this).
//
if ((succNum == (cursor + 1)) && !block->KindIs(BBJ_SWITCH))
{
Expand Down Expand Up @@ -1623,13 +1622,10 @@ void Compiler::fgDumpWasmControlFlow()
BBswtDesc* const desc = block->GetSwitchTargets();
unsigned const caseCount = desc->GetCaseCount();

// BR_TABLE supports a default case, so we need to ensure
// that wasm lower does not remove it.
// BR_TABLE supports a default case.
// Wasm lower should not remove it.
//
// For now, we expect non-wasm lower has made the default case check explicit
// and so our BR_TABLE emission is deficient.
//
assert(!desc->HasDefaultCase());
assert(desc->HasDefaultCase());

if (caseCount == 0)
{
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6 changes: 6 additions & 0 deletions src/coreclr/jit/lower.cpp
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Expand Up @@ -891,6 +891,12 @@ GenTree* Lowering::LowerSwitch(GenTree* node)

noway_assert(jumpCnt >= 2);

#ifdef TARGET_WASM
// Wasm's br_table maps exactly to GT_SWITCH
//
return node->gtNext;
#endif // TARGET_WASM

// Spill the argument to the switch node into a local so that it can be used later.
LIR::Use use(switchBBRange, &(node->AsOp()->gtOp1), node);
ReplaceWithLclVar(use);
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