| commit | 2254755d65a4b8c9bcce6489de9dee5233ac3077 | [log] [tgz] |
|---|---|---|
| author | Nate Biggs <natebiggs@google.com> | Thu Jul 24 11:07:58 2025 -0700 |
| committer | Commit Queue <dart-scoped@luci-project-accounts.iam.gserviceaccount.com> | Thu Jul 24 11:07:58 2025 -0700 |
| tree | 27cb0c2ec2e43ec6713998f36dd63ace4dfcde6f | |
| parent | 02ea7d0b142025cb51b89ed6835b1c94da685cd5 [diff] |
[dart2wasm] Generate br_table for some switch statements. Often switches over enums are exhaustive or nearly exhaustive. The current generator uses identity for the enum values which requires iterating over each value to compare it to the test expression. So each time the switch body is entered is an O(n) operation (where is n is the # of case expressions). This now generates a br_table using the index of the enum and jumps directly to the correct clause, effectively an O(1) operation. A similar approach is taken for switches over an integer range. If the range of case expresison values is close in size to the # of values, it is advantageous to normalize the range around 0 and treat the values themselves as table indices. This approach will also save code size when the index range is dense as the br_table is more compact than the identity/br_if checks. For sparse ranges this may produce a bit more code though only on the order of a few bytes per value in the range. I've added a denseness heuristic to decide when to revert to the current strategy to avoid the code size penalty. Golem benchmark: https://golem.corp.goog/Comparison?repository=dart#targetA%3Ddart2wasm-O2-d8%3BmachineTypeA%3Dlinux-x64%3BrevisionA%3D117402%3BpatchA%3Dnatebiggs-dart2wasm-switch-tables3%3BtargetB%3Ddart2wasm-O2-d8%3BmachineTypeB%3Dlinux-x64%3BrevisionB%3D117401%3BpatchB%3DNone See 100% improvement in SwitchFSM.int and 90% improvement in SwitchFSM.enum. Change-Id: Ie29e8fd59ef6235044ba5b4a4af04023d702ce57 Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/441760 Reviewed-by: Ömer Ağacan <omersa@google.com> Commit-Queue: Nate Biggs <natebiggs@google.com>
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