Proof of concept: reusing typecheck results by psfinaki · Pull Request #18354 · dotnet/fsharp

psfinaki · 2025-03-03T15:50:46Z

This a POC for this feature: #17260
Design doc is here: https://github.com/dotnet/fsharp/blob/main/docs/reusing-typechecking-results.md

The PR shows that the idea is viable, the tests contain examples of the feature working even for multiple files, where changed files use the results of the previous compilation for dependencies.

However, this is far from a proper implementation and, as of now, is supposed to take more time than we can give it. Therefore the effort will be hanging here for a while, welcoming any help to push it through.

See TODOs, comments and other notes. The testing is in place. An overview of big things not implemented yet:

a mechanism to create and merge state deltas
caching and restoring compiler global state, most importantly stamps
pickling and unpickling of tycon references (tcref) without StackOverflows
reduce the cached data size (now about 40 MB for each input and each state)

Also there are some seemingly unrelated old tests failing, needs investigation as well.

github-actions · 2025-03-03T15:51:30Z

⚠️ Release notes required, but author opted out

Warning

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

psfinaki · 2025-03-03T16:02:52Z

src/Compiler/AbstractIL/il.fs


    member _.MetadataIndex = metadataIndex

+    member _.Flags = additionalFlags


This is expected, basic APIs will likely have to increase their surface to make them accessible to the new pickling code.

psfinaki · 2025-03-03T16:04:15Z

src/Compiler/Driver/ParseAndCheckInputs.fs

+
+    let mutable state = tcState
+
+    let results =


So this is apparently a very dumb mechanism of collecting states. Instead, the state "deltas" should be collected and merged here.

psfinaki · 2025-03-03T16:05:16Z

src/Compiler/Driver/ParseAndCheckInputs.fsi

    eagerFormat: (PhasedDiagnostic -> PhasedDiagnostic) *
    inputs: ParsedInput list ->
-        TcState * TopAttribs * CheckedImplFile list * TcEnv
+        TcState * TopAttribs * CheckedImplFile list * TcEnv * TcState list


Also note, TcState list includes the first state. I just kept the first state separately here to decrease the change surface a bit for now.

psfinaki · 2025-03-03T16:05:36Z

src/Compiler/Driver/ReuseTcResults/CachingDriver.fs

@@ -0,0 +1,355 @@
+module internal FSharp.Compiler.ReuseTcResults.CachingDriver
+
+#nowarn "3261"


Nullness warning, don't remove it, just fix it.

psfinaki · 2025-03-03T16:06:10Z

src/Compiler/Driver/ReuseTcResults/CachingDriver.fs

+type CachingDriver(tcConfig: TcConfig) =
+
+    let outputDir = tcConfig.outputDir |> Option.defaultValue ""
+    let tcDataFilePath = Path.Combine(outputDir, "tcComplilationData")


A bunch of files... should eventually have some better structure and naming.

psfinaki · 2025-03-03T16:06:55Z

src/Compiler/Driver/ReuseTcResults/TcResultsImport.fs

+
+let GetSharedData (file, ilScopeRef, ilModule, byteReaderA, byteReaderB) =
+
+    let memA = byteReaderA ()


This is really just copypaste from existing imports... we likely don't need to byte readers and all that stuff can be simplified.

psfinaki · 2025-03-03T16:09:53Z

src/Compiler/Driver/ReuseTcResults/TcResultsPickle.fs

+
+let p_stamp_map pv = p_Map p_stamp pv 
+
+let p_non_null_slot f (x: 'a | null) st =


This is a terrible hack based on top of another terrible hack of even having these slots. This should be eliminated.
It's current used to artificially "backfill" the bindings, instead they should be also cached and restored normally.

It's not that easy to do though. That often leads to SO due to recursion here, or too much data stored - and so on.

psfinaki · 2025-03-03T16:10:12Z

src/Compiler/Driver/ReuseTcResults/TcResultsPickle.fs

+let p_ILTypeDef (x: ILTypeDef) st = 
+    p_string x.Name st
+    //p_type_attributes x.Attributes
+    //p_il_type_def_layout x.Layout


Eventually commented things here should be also pickled and unpickled.

psfinaki · 2025-03-03T16:12:02Z

src/Compiler/Driver/ReuseTcResults/TcResultsPickle.fs

+        (p_tcref "ucref") 
+        p_string 
+        (p_non_null_slot p_entity_spec_new)
+        (a, b, a.binding) 


As noted earlier, bindings should not be pickled separately... instead, the type references should be pickled in a way that they contain all the necessary information to auto-restore the bindings.

psfinaki · 2025-03-03T16:15:28Z

src/Compiler/Driver/ReuseTcResults/TcResultsPickle.fs

+        let tyconRef, typeInstantiation, nullness, binding =
+            u_tup4
+                u_tcref
+                u_tys_new


That's really very, very hard. I haven't come up with a mechanism to properly cache and restore tcref. The compiler needs different info about the entity on different stages (optimizations, tail call checks, code gen, whatever...). And goes through things like typar solutions and referenced entities. But storing it all fully leads to StackOverflows usually...

psfinaki · 2025-03-03T16:16:33Z

src/Compiler/Driver/fsc.fs

        disposables: DisposablesTracker
    ) =

+    CompilerGlobalState.stampCount <- 0L


Horrible hack to keep stamps in tact... instead, the whole state should be cached at the right moment and restored along with the stamps.

psfinaki · 2025-03-03T16:26:35Z

src/Compiler/TypedTree/TypedTreePickle.fs

      if not (inMap.IsLinked n) then
-        warning(Error(FSComp.SR.pickleMissingDefinition (i, inMap.Name, ilscope.QualifiedName), range0))
+
+        // TODO: do not disable


This otherwise creates thousands of warnings... should be fixed properly.

psfinaki · 2025-03-03T16:26:59Z

src/Compiler/TypedTree/TypedTreePickle.fsi

Deleted temporarily just to not fill in all the signatures...

psfinaki · 2025-03-03T16:27:41Z

src/Compiler/FSharp.Compiler.Service.fsproj

    <Content Include="Driver\GraphChecking\Docs.md" />
    <Compile Include="Driver\ParseAndCheckInputs.fsi" />
    <Compile Include="Driver\ParseAndCheckInputs.fs" />
+    <Compile Include="Driver\ReuseTcResults\TcResultsPickle.fs" />


Those should have signatures as well.

psfinaki · 2025-03-04T14:33:34Z

src/Compiler/Driver/ParseAndCheckInputs.fs

+            partialResults, tcState)
+
+    // TODO: collect states here also
+    results, state, []


So yeah it doesn't work for graph checking yet. It should.

psfinaki · 2025-03-04T14:34:46Z

src/Compiler/Driver/ReuseTcResults/CachingDriver.fs

+    let getThisCompilationReferences = Seq.map formatAssemblyReference >> Seq.toArray
+
+    // TODO: don't ignore dependencies
+    let compareGraphs (inputs: ParsedInput list) thisGraph baseGraph : GraphComparisonResult =


Generally, this should be much more robust and paranoid.

psfinaki · 2025-03-04T14:36:29Z

src/Compiler/Driver/ReuseTcResults/TcResultsPickle.fs

+
+let p_tyar_specs_new = (p_list p_tyar_spec_new)
+
+let rec p_ty_new (ty: TType) st : unit =


I introduced here this _new suffix system. Helps to not get lost here, but naming should be better...

psfinaki added 6 commits February 25, 2025 15:16

Reuse typechecking results - stage 1

e31552c

Serialization and deserialization of the typechecking data (#18162)

d9e621f

Refactoring

cec8087

Store typechecking data per file (#18328)

d3788bf

Cache and restore typechecking state (#18336)

3130685

Refactoring

46ff11b

github-project-automation bot added this to F# Compiler and Tooling Mar 3, 2025

github-project-automation bot moved this to New in F# Compiler and Tooling Mar 3, 2025

psfinaki commented Mar 3, 2025

View reviewed changes

Fantomas

c053c70

psfinaki commented Mar 3, 2025

View reviewed changes

src/Compiler/TypedTree/TypedTreePickle.fsi

Copy link

Contributor Author

psfinaki Mar 3, 2025

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Deleted temporarily just to not fill in all the signatures...

psfinaki commented Mar 3, 2025

View reviewed changes

psfinaki commented Mar 4, 2025

View reviewed changes

psfinaki added 2 commits April 4, 2025 15:33

Merge branch 'main' into feature/reuse-typechecking-results

92b70d2

Post-merge

54f8221

psfinaki added the NO_RELEASE_NOTES Label for pull requests which signals, that user opted-out of providing release notes label Apr 4, 2025


		member _.MetadataIndex = metadataIndex

		member _.Flags = additionalFlags

		@@ -0,0 +1,355 @@
		module internal FSharp.Compiler.ReuseTcResults.CachingDriver

		#nowarn "3261"


		let GetSharedData (file, ilScopeRef, ilModule, byteReaderA, byteReaderB) =

		let memA = byteReaderA ()


		let p_stamp_map pv = p_Map p_stamp pv

		let p_non_null_slot f (x: 'a \| null) st =


		let p_tyar_specs_new = (p_list p_tyar_spec_new)

		let rec p_ty_new (ty: TType) st : unit =

Comments

Conversation

psfinaki commented Mar 3, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

github-actions bot commented Mar 3, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

⚠️ Release notes required, but author opted out

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

1 participant

psfinaki commented Mar 3, 2025 •

edited

Loading

github-actions bot commented Mar 3, 2025 •

edited

Loading