Use new Cache api in various places #18872

majocha · 2025-08-29T09:10:40Z

implicitYieldExpressions, argInfoCache, typeDefinitelySubsumesNoCoerceCache, typeFeasibleEquivCache

github-actions · 2025-08-29T09:11:22Z

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Change path	Release notes path	Description
`src/Compiler`	docs/release-notes/.FSharp.Compiler.Service/10.0.100.md	No release notes found or release notes format is not correct
`vsintegration/src`	docs/release-notes/.VisualStudio/18.0.md	No release notes found or release notes format is not correct

majocha · 2025-08-29T09:23:15Z

src/Compiler/Optimize/Optimizer.fs

        // Is it quadratic or quasi-quadratic?
-        if ValueIsUsedOrHasEffect cenv (fun () -> (freeInExpr (CollectLocalsWithStackGuard()) bodyR).FreeLocals) (bindR, bindingInfo) then
+        let collect expr = (freeInExpr (CollectLocalsWithStackGuard()) expr).FreeLocals
+        if ValueIsUsedOrHasEffect cenv (fun () -> (getFreeLocalsCache cenv).GetOrAdd(bodyR, collect)) (bindR, bindingInfo) then


This gives a modest 20% hit ratio in tests. May or may not help somewhat IRL but needs benchmarking.

Looking at Optimization times when building FCS I don't see any speedup.

majocha · 2025-08-29T09:25:59Z

src/Compiler/Utilities/lib.fs

+    /// Usage:
+    ///   let getValueFor = WeakMap.getOrCreate (fun () -> expensiveInit())
+    ///   let v = getValueFor someKey
+    let getOrCreate valueFactory =


Allows to quickly and and-hoc attach a cache instance in various places. Currently we thread various caches along with context objects / records which is not that convenient when testing things out.

auduchinok · 2025-08-29T13:05:54Z

src/Compiler/Checking/Expressions/CheckExpressions.fs

+let getArgInfoCache =
+    let options = Caches.CacheOptions.getDefault() |> Caches.CacheOptions.withNoEviction
+    let factory _ = new Caches.Cache<_, ArgReprInfo>(options, "argInfoCache")
+    WeakMap.getOrCreate factory


Are these caches going to be cleared when asking FCS to clear its caches?

Currently not, I think since they're weakly attached to higher lever stuff, they'll just get GC'd with it. I captured some telemetry and the caches get disposed quite often during the test run.

majocha · 2025-08-30T07:40:18Z

Ahh, there's that memory leak in vs tests, again 😔

T-Gro · 2025-09-04T12:27:08Z

src/Compiler/Checking/Expressions/CheckExpressions.fs

-        env.eCachedImplicitYieldExpressions.Add(synExpr1.Range, (synExpr1, expr1Ty, cachedExpr))
-        try TcExpr cenv overallTy env tpenv otherExpr
-        finally env.eCachedImplicitYieldExpressions.Remove synExpr1.Range
+        (getImplicitYieldExpressionsCache cenv).AddOrUpdate(synExpr1, (expr1Ty, cachedExpr))


The semantics w.r.t. to error handling is different now, aren't they?

Also it feels like the previous version had a race condition (FindAll and later Add), possibly the Multi map was chosen to workaround it by storing a list and not a single value?

Previous version had some concurrency problems, because Vlad at some point added ConcurrentDictionary as HashMultiMap backing store to fix them.

Semantics are different. Originally this just always removed the value in finally. I have to revisit this, I remember the change made sense to me but I forgot why, oh lol. I guess my thinking was eviction will be sufficient here. Now I also notice this was attached to env, not cenv.

This is not really tested in the test suite but there is a benchmark. I'll run it later to see if this still works.

This reverts commit 689112d.

majocha · 2025-09-11T17:17:27Z

I'm trying to identify places that could benefit from memoization or better caching.

Here are some suggestions by Copilot:

InfoReader: immediate members for a type

What: Cache “immediate” metadata enumerations per type:

GetImmediateIntrinsicMethInfosOfTypeAux, GetImmediateIntrinsicPropInfosOfTypeAux

GetImmediateIntrinsicILFieldsOfType, ComputeImmediateIntrinsicEventsOfType

Why: We repeatedly re-enumerate IL metadata and F# members by name for the same types inside hierarchy folds and during overload resolution.

Where: src/Compiler/Checking/InfoReader.fs

Key:

(TypeStructure, optional name filter) for the raw unfiltered enumeration.

Do NOT key by AccessorDomain; cache the raw list and filter per call (Is*Accessible).

Cache result:

MethInfo list (per name or “all”); PropInfo list; ILFieldInfo list; EventInfo list.

Notes:

Factor the existing “…Uncached” helpers to call cached “get all by name” then filter.

Works well for IL types; for F# types, MemberInfo is stable after typecheck.

Method/Property sets along hierarchy

What: Cache folded results:

GetIntrinsicMethodSetsUncached / GetIntrinsicPropertySetsUncached (and named variants)

Why: Same fold gets repeated across overload/resolution passes and “most specific” filtering.

Where: src/Compiler/Checking/InfoReader.fs

Key:

(TypeStructure, optional name, AllowMultiIntfInstantiations) → list<list>

Keep raw sets; filter by AccessorDomain and “most specific” per call.

Notes:

Avoid duplicating per‑call sorting by signature; cache canonicalized lists and reuse.

“Most specific” and equivalence checks for methods

What: Memoize expensive equivalence/specificity predicates:

MethInfosEquivByPartialSig, PropInfosEquivByNameAndPartialSig, GetMostSpecificItemsByType

Why: These perform lots of structural type/equivalence checks in nested loops.

Where: src/Compiler/Checking/InfoReader.fs

Key:

Pairwise (minfo1, minfo2) plus Erasure mode → bool

Notes:

Use a scoped LRU per compilation to avoid unbounded growth.

NameResolution: type lookup tables

What: Cache per‑type “named items” aggregation:

GetIntrinsicNamedItemsUncached

Why: It collects methods, properties, fields, events, traits by name and folds the hierarchy.

Where: src/Compiler/Checking/InfoReader.fs / NameResolution.fs

Key:

(TypeStructure, name) → HierarchyItem

Notes:

Again, filter accessibility at call sites.

I also notice the existing caching in InfoReader seem to exclude generic types. This can't be good. I wonder if it is possible to improve with similar approach to keys / hashing like in type subsumption cache.

majocha · 2025-09-11T21:21:47Z

With aditional type relations caches there seem to be a slight speedup against main:

DecentlySizedStandAloneFileBenchmark

cache-2

| Method | Mean     | Error    | StdDev   | Gen0      | Gen1      | Gen2      | Allocated |
|------- |---------:|---------:|---------:|----------:|----------:|----------:|----------:|
| Run    | 184.8 ms | 10.26 ms | 29.76 ms | 2000.0000 | 1000.0000 | 1000.0000 | 227.98 MB |

| Method | Mean     | Error    | StdDev   | Gen0      | Gen1      | Gen2      | Allocated |
|------- |---------:|---------:|---------:|----------:|----------:|----------:|----------:|
| Run    | 192.5 ms | 10.54 ms | 31.07 ms | 2000.0000 | 1000.0000 | 1000.0000 | 227.95 MB |

| Method | Mean     | Error    | StdDev   | Gen0      | Gen1      | Gen2      | Allocated |
|------- |---------:|---------:|---------:|----------:|----------:|----------:|----------:|
| Run    | 189.5 ms | 10.63 ms | 30.84 ms | 2000.0000 | 1000.0000 | 1000.0000 |    228 MB |

main

| Method | Mean     | Error   | StdDev   | Gen0      | Gen1      | Gen2      | Allocated |
|------- |---------:|--------:|---------:|----------:|----------:|----------:|----------:|
| Run    | 203.5 ms | 8.23 ms | 24.01 ms | 3000.0000 | 2000.0000 | 1000.0000 | 227.19 MB |

| Method | Mean     | Error   | StdDev   | Gen0      | Gen1      | Gen2      | Allocated |
|------- |---------:|--------:|---------:|----------:|----------:|----------:|----------:|
| Run    | 204.7 ms | 8.61 ms | 24.99 ms | 3000.0000 | 2000.0000 | 1000.0000 |    227 MB |

github-project-automation bot added this to F# Compiler and Tooling Aug 29, 2025

github-project-automation bot moved this to New in F# Compiler and Tooling Aug 29, 2025

majocha commented Aug 29, 2025

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auduchinok reviewed Aug 29, 2025

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majocha force-pushed the cache-2 branch from 3c7d950 to 0bd3211 Compare August 29, 2025 17:47

majocha mentioned this pull request Aug 30, 2025

Type subsumption cache, fix keys to reduce memory use #18875

Merged

majocha added 2 commits September 3, 2025 15:48

optimizer

6b0f7d5

argInfo + implicit yield

208362a

majocha force-pushed the cache-2 branch from 476dcb6 to 208362a Compare September 3, 2025 13:50

majocha added 2 commits September 4, 2025 09:35

fix comment

4925224

Merge branch 'main' into cache-2

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T-Gro reviewed Sep 4, 2025

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majocha added 12 commits September 4, 2025 17:30

Merge branch 'main' into cache-2

bd5a72f

see if this helps

8d32412

wip

689112d

Revert "wip"

13d4dd1

This reverts commit 689112d.

log min threads

7543b43

?

859fdac

force immediate eviction in some test runs

873a945

.

03a606d

Merge branch 'main' into cache-2

dedb3ee

.

e6fc866

format

4d69ae5

.

942640b

majocha force-pushed the cache-2 branch from 94879d3 to 942640b Compare September 5, 2025 15:40

majocha added 2 commits September 8, 2025 21:53

Merge branch 'main' into cache-2

d3fd87b

add a test

aac2a46

majocha added 3 commits September 9, 2025 21:09

restore optimizer

57c8f3f

additional type rel caches

078b49f

Merge branch 'main' into cache-2

e4d45f4

majocha added 4 commits September 14, 2025 22:39

while loop

128e847

Merge branch 'main' into cache-2

3d6c92c

Merge branch 'main' into cache-2

d3dbcd1

Merge branch 'main' into cache-2

14a7822

majocha force-pushed the cache-2 branch from 3033da3 to 14a7822 Compare September 17, 2025 13:46

majocha added 8 commits September 17, 2025 17:28

don't unload ad

f6c3319

server gc in netcore tests

62dc77f

collect stats better

930d871

show stats in vs output pane

af601bb

fix method missing at runtime - ns2.0 haha

66a5ba7

format

bd7c24d

Merge branch 'main' into cache-2

8f550ae

write cache stats to console with --times

ee47601

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