Stream: git-wasmtime

Topic: wasmtime / PR #13923 Cranelift: Avoid some hashmaps on th...

Wasmtime GitHub notifications bot (Jul 21 2026 at 16:21):

fitzgen opened PR #13923 from fitzgen:avoid-some-hashmaps-when-lowering to bytecodealliance:main:

This commit implements three optimizations for lowering's hot path:

• Compute instruction constants on demand instead of caching them in a hashmap. The well-predicted match on a dense dfg.insts element is cheaper than the random-access hash probe, and this also removes the cached hashmap construction at setup too.

• Make side_effect_inst_entry_colors a dense SecondaryMap<Inst, InstColor> instead of a hashmap. cur_color reaches at least 1 before processing any instruction, so the default InstColor(0) is available as a "not side-effecting" sentinel. This replaces hash probing with array indexing and lets get_value_as_source_or_const and lower_clif_block reuse one dense read for both the side-effect test and the color, dropping a redundant has_lowering_side_effect recompute per source instruction.

• Iterate the lowered block order by index in Lower::lower instead of cloning it into a SmallVec (that likely must heap allocate), removing a per-function allocation.

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Wasmtime GitHub notifications bot (Jul 21 2026 at 16:21):

fitzgen requested cfallin for a review on PR #13923.

Wasmtime GitHub notifications bot (Jul 21 2026 at 16:21):

fitzgen requested wasmtime-compiler-reviewers for a review on PR #13923.

Wasmtime GitHub notifications bot (Jul 21 2026 at 16:25):

:thumbs_up: cfallin submitted PR review:

Thanks!

Wasmtime GitHub notifications bot (Jul 21 2026 at 16:25):

:speech_balloon: cfallin created PR review comment:

Subjective style nit but: no need for the history-narrative comment here IIRC -- most of our algorithms compute what they need on demand, and caching is the exception that would need explanation.

Wasmtime GitHub notifications bot (Jul 21 2026 at 16:26):

fitzgen updated PR #13923.

Wasmtime GitHub notifications bot (Jul 21 2026 at 16:27):

fitzgen has enabled auto merge for PR #13923.

Wasmtime GitHub notifications bot (Jul 21 2026 at 16:38):

fitzgen added PR #13923 Cranelift: Avoid some hashmaps on the lowering hot path to the merge queue.

Wasmtime GitHub notifications bot (Jul 21 2026 at 17:03):

github-merge-queue[bot] removed PR #13923 Cranelift: Avoid some hashmaps on the lowering hot path from the merge queue.

Wasmtime GitHub notifications bot (Jul 21 2026 at 17:09):

fitzgen added PR #13923 Cranelift: Avoid some hashmaps on the lowering hot path to the merge queue.

Wasmtime GitHub notifications bot (Jul 21 2026 at 17:35):

:check: fitzgen merged PR #13923.

Wasmtime GitHub notifications bot (Jul 21 2026 at 17:35):

fitzgen removed PR #13923 Cranelift: Avoid some hashmaps on the lowering hot path from the merge queue.

Last updated: Jul 29 2026 at 05:03 UTC