Replace Map with Dictionary

src/Compiler/Checking/import.fs

@@ -5,6 +5,7 @@ module internal FSharp.Compiler.Import
 
 open System.Collections.Concurrent
 open System.Collections.Generic
+open System.Collections.Immutable
 open Internal.Utilities.Library
 open Internal.Utilities.Library.Extras
 open FSharp.Compiler 
@@ -586,25 +587,60 @@ let ImportILAssemblyTypeDefs (amap, m, auxModLoader, aref, mainmod: ILModuleDef)
     CombineCcuContentFragments m (mainmod :: mtypsForExportedTypes)
 
 /// Import the type forwarder table for an IL assembly
-let ImportILAssemblyTypeForwarders (amap, m, exportedTypes: ILExportedTypesAndForwarders) = 
-    // Note 'td' may be in another module or another assembly!
-    // Note: it is very important that we call auxModLoader lazily
-    [ //printfn "reading forwarders..." 
-        for exportedType in exportedTypes.AsList() do 
+let ImportILAssemblyTypeForwarders (amap, m, exportedTypes: ILExportedTypesAndForwarders): CcuTypeForwarderTable =            
+    let rec addToTree tree path item value =
+        match path with
+        | [] ->
+            { tree with
+                Children =
+                    tree.Children.Add(
+                        item,
+                        { Value = Some value
+                          Children = ImmutableDictionary.Empty }
+                    ) }
+        | nodeKey :: rest ->
+            match tree.Children.TryGetValue(nodeKey) with
+            | true, subTree -> { tree with Children = tree.Children.SetItem(nodeKey, addToTree subTree rest item value) }
+            | false, _ -> { tree with Children = tree.Children.Add(nodeKey, mkTreeWith rest item value) }
+
+    and mkTreeWith path item value =
+        match path with
+        | [] ->
+            { Value = None
+              Children =
+                ImmutableDictionary.Empty.Add(
+                    item,
+                    { Value = Some value
+                      Children = ImmutableDictionary.Empty }
+                ) }
+        | nodeKey :: rest ->
+            { Value = None
+              Children = ImmutableDictionary.Empty.Add(nodeKey, mkTreeWith rest item value) }
+
+    let rec addNested
+        (exportedType: ILExportedTypeOrForwarder)
+        (nets: ILNestedExportedTypes)
+        (enc: string list)
+        (tree: CcuTypeForwarderTree<string, Lazy<EntityRef>>)
+        : CcuTypeForwarderTree<string, Lazy<EntityRef>> =
+        (tree, nets.AsList())
+        ||> List.fold(fun tree net ->
+            let tcref = lazy ImportILTypeRefUncached (amap ()) m (ILTypeRef.Create(exportedType.ScopeRef, enc, net.Name))
+            addToTree tree enc exportedType.Name tcref
+            |> addNested exportedType net.Nested [yield! enc; yield net.Name])
+
+    match exportedTypes.AsList() with
+    | [] -> CcuTypeForwarderTable.Empty
+    | rootTypes ->
+        ({ Value = None; Children = ImmutableDictionary.Empty } , rootTypes)
+        ||> List.fold(fun tree exportedType ->
             let ns, n = splitILTypeName exportedType.Name
-            //printfn "found forwarder for %s..." n
-            let tcref = lazy ImportILTypeRefUncached (amap()) m (ILTypeRef.Create(exportedType.ScopeRef, [], exportedType.Name))
-            yield (Array.ofList ns, n), tcref
-            let rec nested (nets: ILNestedExportedTypes) enc = 
-                [ for net in nets.AsList() do 
-
-                    //printfn "found nested forwarder for %s..." net.Name
-                    let tcref = lazy ImportILTypeRefUncached (amap()) m (ILTypeRef.Create (exportedType.ScopeRef, enc, net.Name))
-                    yield (Array.ofList enc, exportedType.Name), tcref 
-                    yield! nested net.Nested (enc @ [ net.Name ]) ]
-            yield! nested exportedType.Nested (ns@[n]) 
-    ] |> Map.ofList
-
+            let tcref = lazy ImportILTypeRefUncached (amap ()) m (ILTypeRef.Create(exportedType.ScopeRef, [], exportedType.Name))
+            addToTree tree ns n tcref
+            |> addNested exportedType exportedType.Nested [yield! ns; yield n]
+        )
+        |> fun root -> { Root = root }
+
 /// Import an IL assembly as a new TAST CCU
 let ImportILAssembly(amap: unit -> ImportMap, m, auxModuleLoader, xmlDocInfoLoader: IXmlDocumentationInfoLoader option, ilScopeRef, sourceDir, fileName, ilModule: ILModuleDef, invalidateCcu: IEvent<string>) = 
     invalidateCcu |> ignore
@@ -616,7 +652,7 @@ let ImportILAssembly(amap: unit -> ImportMap, m, auxModuleLoader, xmlDocInfoLoad
     let mty = ImportILAssemblyTypeDefs(amap, m, auxModuleLoader, aref, ilModule)
     let forwarders = 
         match ilModule.Manifest with 
-        | None -> Map.empty
+        | None -> CcuTypeForwarderTable.Empty
         | Some manifest -> ImportILAssemblyTypeForwarders(amap, m, manifest.ExportedTypes)
 
     let ccuData: CcuData = 

src/Compiler/Checking/import.fsi

@@ -3,6 +3,7 @@
 /// Functions to import .NET binary metadata as TAST objects
 module internal FSharp.Compiler.Import
 
+open System.Collections.Immutable
 open Internal.Utilities.Library
 open FSharp.Compiler.AbstractIL.IL
 open FSharp.Compiler.TcGlobals
@@ -96,7 +97,7 @@ val internal ImportILAssembly:
 
 /// Import the type forwarder table for an IL assembly
 val internal ImportILAssemblyTypeForwarders:
-    (unit -> ImportMap) * range * ILExportedTypesAndForwarders -> Map<string array * string, Lazy<EntityRef>>
+    (unit -> ImportMap) * range * ILExportedTypesAndForwarders -> CcuTypeForwarderTable
 
 /// Import an IL type as an F# type, first rescoping to view the metadata from the current assembly
 /// being compiled. importInst gives the context for interpreting type variables.

src/Compiler/Driver/CompilerImports.fs

@@ -6,6 +6,7 @@ module internal FSharp.Compiler.CompilerImports
 
 open System
 open System.Collections.Generic
+open System.Collections.Immutable
 open System.Diagnostics
 open System.IO
 
@@ -1114,7 +1115,7 @@ and [<Sealed>] TcImports(tcConfigP: TcConfigProvider, initialResolutions: TcAsse
                 MemberSignatureEquality = (fun ty1 ty2 -> typeEquivAux EraseAll g ty1 ty2)
                 ImportProvidedType = (fun ty -> ImportProvidedType (tcImports.GetImportMap()) m ty)
                 TryGetILModuleDef = (fun () -> Some ilModule)
-                TypeForwarders = Map.empty
+                TypeForwarders = CcuTypeForwarderTable.Empty
                 XmlDocumentationInfo =
                     match tcConfig.xmlDocInfoLoader with
                     | Some xmlDocInfoLoader -> xmlDocInfoLoader.TryLoad(fileName)

src/Compiler/Driver/ParseAndCheckInputs.fs

@@ -5,6 +5,7 @@ module internal FSharp.Compiler.ParseAndCheckInputs
 
 open System
 open System.IO
+open System.Collections.Generic
 
 open Internal.Utilities.Collections
 open Internal.Utilities.Library
@@ -727,7 +728,7 @@ let CheckSimulateException(tcConfig: TcConfig) =
     | Some("tc-oe") -> raise(OverflowException())
     | Some("tc-atmm") -> raise(ArrayTypeMismatchException())
     | Some("tc-bif") -> raise(BadImageFormatException())
-    | Some("tc-knf") -> raise(System.Collections.Generic.KeyNotFoundException())
+    | Some("tc-knf") -> raise(KeyNotFoundException())
     | Some("tc-ior") -> raise(IndexOutOfRangeException())
     | Some("tc-ic") -> raise(InvalidCastException())
     | Some("tc-ip") -> raise(InvalidProgramException())
@@ -808,7 +809,7 @@ let GetInitialTcState(m, ccuName, tcConfig: TcConfig, tcGlobals, tcImports: TcIm
           ILScopeRef=ILScopeRef.Local
           Contents=ccuContents
           MemberSignatureEquality= typeEquivAux EraseAll tcGlobals
-          TypeForwarders=Map.empty
+          TypeForwarders= CcuTypeForwarderTable.Empty
           XmlDocumentationInfo = None }
 
     let ccu = CcuThunk.Create(ccuName, ccuData)

src/Compiler/TypedTree/TypedTree.fs

@@ -4,7 +4,8 @@
 module internal rec FSharp.Compiler.TypedTree 
 
 open System
-open System.Collections.Generic 
+open System.Collections.Generic
+open System.Collections.Immutable
 open System.Diagnostics
 open System.Reflection
 
@@ -5291,8 +5292,39 @@ type CcuData =
 
     override x.ToString() = sprintf "CcuData(%A)" x.FileName
 
+type CcuTypeForwarderTree<'TKey, 'TValue> =
+    {
+        Value : 'TValue option
+        Children : ImmutableDictionary<'TKey, CcuTypeForwarderTree<'TKey, 'TValue>>
+    }
+
+    static member Empty = { Value = None; Children = ImmutableDictionary.Empty }
+
+module CcuTypeForwarderTable =
+    let rec findInTree (remainingPath: ArraySegment<string>) (finalKey : string) (tree:CcuTypeForwarderTree<string, Lazy<EntityRef>>): Lazy<EntityRef> option =
+        let nodes = tree.Children
+        let searchTerm =
+            if remainingPath.Count = 0 then
+                finalKey
+            else
+                remainingPath.Array.[remainingPath.Offset]
+        match nodes.TryGetValue searchTerm with
+        | true, innerTree ->
+            if remainingPath.Count = 0 then
+                innerTree.Value
+            else
+                 findInTree (ArraySegment<string>(remainingPath.Array, remainingPath.Offset + 1, remainingPath.Count - 1)) finalKey innerTree
+        | false, _ -> None
+
 /// Represents a table of .NET CLI type forwarders for an assembly
-type CcuTypeForwarderTable = Map<string[] * string, Lazy<EntityRef>>
+type CcuTypeForwarderTable =
+    {
+        Root : CcuTypeForwarderTree<string, Lazy<EntityRef>>
+    }
+
+    static member Empty : CcuTypeForwarderTable = { Root = CcuTypeForwarderTree<_,_>.Empty }   
+    member this.TryGetValue (path:string array) (item:string): Lazy<EntityRef> option =
+        CcuTypeForwarderTable.findInTree (ArraySegment path) item this.Root
 
 type CcuReference = string // ILAssemblyRef
 
@@ -5381,7 +5413,7 @@ type CcuThunk =
     member ccu.Contents = ccu.Deref.Contents
 
     /// The table of type forwarders for this assembly
-    member ccu.TypeForwarders: Map<string[] * string, Lazy<EntityRef>> = ccu.Deref.TypeForwarders
+    member ccu.TypeForwarders: CcuTypeForwarderTable = ccu.Deref.TypeForwarders
 
     /// The table of modules and namespaces at the "root" of the assembly
     member ccu.RootModulesAndNamespaces = ccu.Contents.ModuleOrNamespaceType.ModuleAndNamespaceDefinitions
@@ -5418,10 +5450,8 @@ type CcuThunk =
     /// Try to resolve a path into the CCU by referencing the .NET/CLI type forwarder table of the CCU
     member ccu.TryForward(nlpath: string[], item: string) : EntityRef option = 
         ccu.EnsureDerefable nlpath
-        let key = nlpath, item
-        match ccu.TypeForwarders.TryGetValue key with
-        | true, entity -> Some(entity.Force())
-        | _ -> None
+        ccu.TypeForwarders.TryGetValue nlpath item
+        |> Option.map (fun entity -> entity.Force())
 
     /// Used to make forward calls into the type/assembly loader when comparing member signatures during linking
     member ccu.MemberSignatureEquality(ty1: TType, ty2: TType) = 

tests/benchmarks/FCSSourceFiles/FCSSourceFiles.fsproj

@@ -0,0 +1,20 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net6.0</TargetFramework>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <Compile Include="Program.fs" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <PackageReference Include="BenchmarkDotNet" Version="0.13.1" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\..\..\src\Compiler\FSharp.Compiler.Service.fsproj" />
+  </ItemGroup>
+
+</Project>