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[MicroPerf] Eliminate closure allocations in well-known-attribute queries - #20423

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t-gro-attr-query-closures
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[MicroPerf] Eliminate closure allocations in well-known-attribute queries#20423
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t-gro-attr-query-closures

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@T-Gro T-Gro commented Sep 2, 2026

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Well-known-attribute queries partially applied computeEntityWellKnownFlags g / computeValWellKnownFlags g to non-inline caching methods, so each query heap-allocated an FSharpFunc even on a cache hit. The queries now test a function-free NeedsCompute bit and compute (on a miss only) with a fully-applied call; an inline Array.tryPick twin folds the remaining lambda.

Closure allocation eliminated — gc-verbose sampled, fsc self-compiling the 455-file FSharp.Compiler.Service (Release/net11):

closure site before after
tryFindILAttribByFlag@204 87.6 MB 0
EntityTryGetBoolAttribute@734 55.2 MB 0
ArgReprInfoHasWellKnownAttribute@716 31.0 MB 0
check result
closure classes in emitted FSharp.Compiler.Service.dll 3 on main → 0 here
FSharp.Compiler.Service.dll size −21,504 bytes
diff +63 / −73, 7 files
behaviour cached flag values identical; attribute/accessibility ComponentTests pass

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T-Gro requested a review from a team as a code owner September 2, 2026 10:33
@T-Gro T-Gro added Theme-Performance NO_RELEASE_NOTES Label for pull requests which signals, that user opted-out of providing release notes labels Sep 2, 2026
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T-Gro requested a review from abonie September 2, 2026 10:33
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⚠️ Release notes required, but author opted out

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Author opted out of release notes, check is disabled for this pull request.
cc @dotnet/fsharp-team-msft

@github-actions github-actions Bot added the AI-Tooling-Check-Bypassed Tooling check: non-fork PR, not diff-analyzed label Sep 2, 2026
auduchinok
auduchinok reviewed Sep 2, 2026
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Comment thread src/Compiler/TypedTree/TypedTreeOps.Attributes.fs Outdated
perf-bundle and others added 2 commits September 7, 2026 14:47
perf-bundle
Eliminate closure allocations in well-known-attribute queries
c2f078d 
The well-known-attribute query helpers partially applied computeXxx g to
non-inline caching methods (CheckFlag / HasWellKnownAttribute(flag,compute)),
allocating a closure on every query even on cache hits. Replace that with a
two-phase form: test a function-free NeedsCompute bit, and on a miss classify
with a fully-applied computeXxx g attribs (a plain call, no closure), store,
then do function-free bit tests. Also add an inline Array.tryPick twin in
Internal.Utilities.Library that shadows FSharp.Core's at tryFindILAttribByFlag,
folding that lambda closure. Behavior is unchanged (per-entity/val caching
still lives in the flag bitfield). Removes the now-dead CheckFlag /
compute-overload methods.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
perf-bundle
Deduplicate well-known value attribute caching
8501fde 
Use an inline helper with an InlineIfLambda setter so Val and argument queries share cache initialization without reintroducing closure allocations.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
@T-Gro
T-Gro force-pushed the t-gro-attr-query-closures branch from 9dcc9f3 to 8501fde Compare September 7, 2026 12:50
@T-Gro
T-Gro enabled auto-merge (squash) September 8, 2026 07:45
@github-project-automation github-project-automation Bot moved this from New to In Progress in F# Compiler and Tooling Sep 9, 2026
@T-Gro
T-Gro merged commit 2ef03e9 into main Sep 9, 2026
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bartelink pushed a commit to bartelink/fsharp that referenced this pull request Oct 7, 2026
@T-Gro perf-bundle
@bartelink
[MicroPerf] Eliminate closure allocations in well-known-attribute que…
896dce2 
…ries (dotnet#20423)

* Eliminate closure allocations in well-known-attribute queries

The well-known-attribute query helpers partially applied computeXxx g to
non-inline caching methods (CheckFlag / HasWellKnownAttribute(flag,compute)),
allocating a closure on every query even on cache hits. Replace that with a
two-phase form: test a function-free NeedsCompute bit, and on a miss classify
with a fully-applied computeXxx g attribs (a plain call, no closure), store,
then do function-free bit tests. Also add an inline Array.tryPick twin in
Internal.Utilities.Library that shadows FSharp.Core's at tryFindILAttribByFlag,
folding that lambda closure. Behavior is unchanged (per-entity/val caching
still lives in the flag bitfield). Removes the now-dead CheckFlag /
compute-overload methods.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

* Deduplicate well-known value attribute caching

Use an inline helper with an InlineIfLambda setter so Val and argument queries share cache initialization without reintroducing closure allocations.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

---------

Co-authored-by: perf-bundle <perf@local>
Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
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