[Wasm RyuJit] Slightly smaller code for switches #122198
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Wasm switches (`br_table`) have a default case, so take advantage of this and stop peeling off the default case in lower.
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@dotnet/jit-contrib PTAL |
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Pull request overview
This PR optimizes WebAssembly switch statement code generation by leveraging the native default case support in Wasm's br_table instruction. Previously, the JIT would peel off the default case during lowering; this change preserves it for Wasm targets, resulting in smaller generated code.
Key changes:
- Modified switch lowering to skip default case peeling for Wasm targets
- Updated assertions and comments throughout to reflect that Wasm switches now retain their default cases
- Adjusted optimization passes to handle the different switch IR representation on Wasm (GT_SWITCH vs GT_SWITCH_TABLE)
Reviewed changes
Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.
| File | Description |
|---|---|
| src/coreclr/jit/lower.cpp | Added early return for TARGET_WASM in LowerSwitch to prevent default case peeling |
| src/coreclr/jit/fgwasm.cpp | Updated comments and changed assertion from !HasDefaultCase() to HasDefaultCase() to reflect new behavior |
| src/coreclr/jit/fgopt.cpp | Added TARGET_WASM conditional for switchTree operator assertion (GT_SWITCH vs GT_SWITCH_TABLE) |
| src/coreclr/jit/codegenwasm.cpp | Updated assertion to expect default case and added assertion for empty switch fallthrough case |
This was referenced Dec 5, 2025
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adamperlin
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Dec 8, 2025
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This looks good to me! It's neat we can completely map GT_SWITCH -> br_table
This was referenced Dec 9, 2025
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Tagging subscribers to 'arch-wasm': @lewing, @pavelsavara |
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Wasm switches (
br_table) have a default case, so take advantage of this and stop peeling off the default case in lower.