Some minor perf improvements

src/Compiler/AbstractIL/ilwrite.fs

@@ -3215,7 +3215,7 @@ let count f arr =
 module FileSystemUtilities =
     open System.Reflection
     open System.Globalization
-    let progress = try Environment.GetEnvironmentVariable("FSharp_DebugSetFilePermissions") <> null with _ -> false
+    let progress = try not (isNull (Environment.GetEnvironmentVariable("FSharp_DebugSetFilePermissions"))) with _ -> false
 
 /// Arbitrary value
 [<Literal>]

src/Compiler/Driver/CompilerDiagnostics.fs

@@ -616,10 +616,11 @@ module OldStyleMessages =
 let mutable showParserStackOnParseError = false
 #endif
 
+[<return: Struct>]
 let (|InvalidArgument|_|) (exn: exn) =
     match exn with
-    | :? ArgumentException as e -> Some e.Message
-    | _ -> None
+    | :? ArgumentException as e -> ValueSome e.Message
+    | _ -> ValueNone
 
 let OutputNameSuggestions (os: StringBuilder) suggestNames suggestionsF idText =
     if suggestNames then

src/Compiler/Driver/CreateILModule.fs

@@ -54,11 +54,12 @@ module AttributeHelpers =
             | Some(Attrib(_, _, [ AttribBoolArg p ], _, _, _, _)) -> Some p
             | _ -> None
 
+    [<return: Struct>]
     let (|ILVersion|_|) (versionString: string) =
         try
-            Some(parseILVersion versionString)
+            ValueSome(parseILVersion versionString)
         with e ->
-            None
+            ValueNone
 
 //----------------------------------------------------------------------------
 // ValidateKeySigningAttributes, GetStrongNameSigner

src/Compiler/Facilities/DiagnosticsLogger.fs

@@ -69,10 +69,11 @@ exception StopProcessingExn of exn option with
         | StopProcessingExn(Some exn) -> "StopProcessingExn, originally (" + exn.ToString() + ")"
         | _ -> "StopProcessingExn"
 
+[<return: Struct>]
 let (|StopProcessing|_|) exn =
     match exn with
-    | StopProcessingExn _ -> Some()
-    | _ -> None
+    | StopProcessingExn _ -> ValueSome()
+    | _ -> ValueNone
 
 let StopProcessing<'T> = StopProcessingExn None
 

src/Compiler/Facilities/DiagnosticsLogger.fsi

@@ -39,7 +39,7 @@ val NoSuggestions: Suggestions
 /// Thrown when we stop processing the F# Interactive entry or #load.
 exception StopProcessingExn of exn option
 
-val (|StopProcessing|_|): exn: exn -> unit option
+val (|StopProcessing|_|): exn: exn -> unit voption
 
 val StopProcessing<'T> : exn
 

src/Compiler/Service/TransparentCompiler.fs

@@ -1155,7 +1155,7 @@ type internal TransparentCompiler
 
             //Trace.TraceInformation("\n" + debugGraph)
 
-            if Activity.Current <> null then
+            if not (isNull (Activity.Current)) then
                 Activity.Current.AddTag("graph", debugGraph) |> ignore
 
             return nodeGraph, graph

src/Compiler/TypedTree/TypedTree.fs

@@ -5933,7 +5933,7 @@ type Construct() =
                                    match baseType with 
                                    | null -> false
                                    | x when x.IsGenericType -> false
-                                   | x when x.DeclaringType <> null -> false
+                                   | x when not (isNull (x.DeclaringType)) -> false
                                    | x -> x.FullName = "System.Delegate" || x.FullName = "System.MulticastDelegate"), m))
               IsEnum = st.PUntaint((fun st -> st.IsEnum), m)
               IsStructOrEnum = st.PUntaint((fun st -> st.IsValueType || st.IsEnum), m)

src/Compiler/Utilities/LruCache.fs

@@ -36,7 +36,7 @@ type internal LruCache<'TKey, 'TVersion, 'TValue when 'TKey: equality and 'TVers
     let weakList = LinkedList<'TKey * 'TVersion * string * ValueLink<'TValue>>()
 
     let rec removeCollected (node: LinkedListNode<_>) =
-        if node <> null then
+        if not (isNull node) then
             let key, version, label, value = node.Value
 
             match value with
@@ -63,7 +63,7 @@ type internal LruCache<'TKey, 'TVersion, 'TValue when 'TKey: equality and 'TVers
 
             let mutable node = weakList.Last
 
-            while weakList.Count > keepWeakly && node <> null do
+            while weakList.Count > keepWeakly && not (isNull node) do
                 let previous = node.Previous
                 let key, version, label, _ = node.Value
                 weakList.Remove node
@@ -80,7 +80,7 @@ type internal LruCache<'TKey, 'TVersion, 'TValue when 'TKey: equality and 'TVers
 
         let mutable anythingWeakened = false
 
-        while strongList.Count > keepStrongly && node <> null do
+        while strongList.Count > keepStrongly && not (isNull node) do
             let previous = node.Previous
 
             match node.Value with

src/Compiler/Utilities/illib.fs

@@ -639,8 +639,7 @@ module List =
     let duplicates (xs: 'T list) =
         xs
         |> List.groupBy id
-        |> List.filter (fun (_, elems) -> Seq.length elems > 1)
-        |> List.map fst
+        |> List.choose (fun (key, elems) -> if Seq.length elems > 1 then Some key else None)
 
     let internal allEqual (xs: 'T list) =
         match xs with
@@ -802,15 +801,17 @@ module String =
     /// Splits a string into substrings based on the strings in the array separators
     let split options (separator: string[]) (value: string) = value.Split(separator, options)
 
+    [<return: Struct>]
     let (|StartsWith|_|) pattern value =
-        if String.IsNullOrWhiteSpace value then None
-        elif value.StartsWithOrdinal pattern then Some()
-        else None
+        if String.IsNullOrWhiteSpace value then ValueNone
+        elif value.StartsWithOrdinal pattern then ValueSome()
+        else ValueNone
 
+    [<return: Struct>]
     let (|Contains|_|) pattern value =
-        if String.IsNullOrWhiteSpace value then None
-        elif value.Contains pattern then Some()
-        else None
+        if String.IsNullOrWhiteSpace value then ValueNone
+        elif value.Contains pattern then ValueSome()
+        else ValueNone
 
     let getLines (str: string) =
         use reader = new StringReader(str)

src/Compiler/Utilities/illib.fsi

@@ -296,9 +296,9 @@ module internal String =
     /// Splits a string into substrings based on the strings in the array separators
     val split: options: StringSplitOptions -> separator: string[] -> value: string -> string[]
 
-    val (|StartsWith|_|): pattern: string -> value: string -> unit option
+    val (|StartsWith|_|): pattern: string -> value: string -> unit voption
 
-    val (|Contains|_|): pattern: string -> value: string -> unit option
+    val (|Contains|_|): pattern: string -> value: string -> unit voption
 
     val getLines: str: string -> string[]
 

src/Compiler/Utilities/lib.fs

@@ -312,7 +312,9 @@ type Graph<'Data, 'Id when 'Id : comparison and 'Id : equality>
     let tab = Map.ofList nodes
     let nodes = List.map snd nodes
     do for node in nodes do
-        node.nodeNeighbours <- edges |> List.filter (fun (x, _y) -> x = node.nodeId) |> List.map (fun (_, nodeId) -> tab[nodeId])
+        node.nodeNeighbours <-
+            edges
+            |> List.choose (fun (x, nodeId) -> if x = node.nodeId then Some tab[nodeId] else None)
 
     member g.GetNodeData nodeId = tab[nodeId].nodeData
 

src/Compiler/pars.fsy

@@ -6633,7 +6633,7 @@ nameop:
 
 identExpr:
   | ident
-     { if $1.idText = "" then
+     { if System.String.IsNullOrEmpty $1.idText then
            SynExpr.FromParseError(SynExpr.Ident($1), $1.idRange)
        else
            SynExpr.Ident($1) }

src/fsi/console.fs

@@ -31,16 +31,11 @@ type internal History() =
         current <- -1
 
     member _.Add line =
-        match line with
-        | null
-        | "" -> ()
-        | _ -> list.Add(line)
+        if not (String.IsNullOrWhiteSpace line) then
+            list.Add line
 
     member _.AddLast line =
-        match line with
-        | null
-        | "" -> ()
-        | _ ->
+        if not (String.IsNullOrWhiteSpace line) then
             list.Add(line)
             current <- list.Count
 
@@ -539,7 +534,7 @@ type internal ReadLineConsole() =
             let previous = history.Previous()
             history.Next() |> ignore
 
-            if previous = "" then
+            if String.IsNullOrEmpty previous then
                 setPrompt true
             else
                 setPrompt (previous.EndsWith(";;"))

tests/FSharp.Compiler.ComponentTests/Conformance/Types/UnionTypes/UnionStructTypes.fs

@@ -695,7 +695,7 @@ type StructUnion =
 
         for i=1 to countOfCases do
             let t = basicTypes[i%basicTypes.Length]
-            if t = "" then 
+            if System.String.IsNullOrEmpty t then 
                 codeSb.AppendLine($"  | Case{i}") |> ignore
             else
                 codeSb.AppendLine($"  | Case{i} of field1_{i}:{t} * field2_{i}:{t}") |> ignore

tests/FSharp.Compiler.ComponentTests/TypeChecks/Graph/FileContentMappingTests.fs

@@ -9,31 +9,35 @@ let private getContent isSignature sourceCode =
     let ast = parseSourceCode ("Test.fs", sourceCode)
     FileContentMapping.mkFileContent { Idx = 0; FileName = fileName; ParsedInput = ast }
 
+[<return: Struct>]
 let private (|TopLevelNamespace|_|) value e =
     match e with
     | FileContentEntry.TopLevelNamespace(path, content) ->
         let combined = String.concat "." path
-        if combined = value then Some content else None
-    | _ -> None
+        if combined = value then ValueSome content else ValueNone
+    | _ -> ValueNone
 
+[<return: Struct>]
 let private (|OpenStatement|_|) value e =
     match e with
     | FileContentEntry.OpenStatement path ->
         let combined = String.concat "." path
-        if combined = value then Some() else None
-    | _ -> None
+        if combined = value then ValueSome() else ValueNone
+    | _ -> ValueNone
 
+[<return: Struct>]
 let private (|PrefixedIdentifier|_|) value e =
     match e with
     | FileContentEntry.PrefixedIdentifier path ->
         let combined = String.concat "." path
-        if combined = value then Some() else None
-    | _ -> None
+        if combined = value then ValueSome() else ValueNone
+    | _ -> ValueNone
 
+[<return: Struct>]
 let private (|NestedModule|_|) value e =
     match e with
-    | FileContentEntry.NestedModule(name, nestedContent) -> if name = value then Some(nestedContent) else None
-    | _ -> None
+    | FileContentEntry.NestedModule(name, nestedContent) -> if name = value then ValueSome(nestedContent) else ValueNone
+    | _ -> ValueNone
 
 [<Test>]
 let ``Top level module only exposes namespace`` () =

tests/FSharp.Compiler.UnitTests/BuildGraphTests.fs

@@ -17,7 +17,7 @@ module BuildGraphTests =
     let private createNode () =
         let o = obj ()
         GraphNode(node { 
-            Assert.shouldBeTrue (o <> null)
+            Assert.shouldBeTrue (not (isNull o))
             return 1 
         }), WeakReference(o)
 
@@ -149,7 +149,7 @@ module BuildGraphTests =
             | :? OperationCanceledException as ex ->
                 ex
 
-        Assert.shouldBeTrue(ex <> null)
+        Assert.shouldBeTrue(not (isNull ex))
 
     [<Fact>]
     let ``A request can cancel 2``() =
@@ -179,7 +179,7 @@ module BuildGraphTests =
             | :? OperationCanceledException as ex ->
                 ex
 
-        Assert.shouldBeTrue(ex <> null)
+        Assert.shouldBeTrue(not (isNull ex))
         try task.Wait(1000) |> ignore with | :? TimeoutException -> reraise() | _ -> ()
 
     [<Fact>]

tests/FSharp.Test.Utilities/CompilerAssert.fs

@@ -619,7 +619,7 @@ module rec CompilerAssertHelpers =
                     func ()
                     true, None
                 with e ->
-                    let errorMessage = if e.InnerException <> null then e.InnerException.ToString() else e.ToString()
+                    let errorMessage = if not (isNull (e.InnerException)) then e.InnerException.ToString() else e.ToString()
                     stderr.Append errorMessage |> ignore
                     false, Some e
             finally

tests/scripts/scriptlib.fsx

@@ -17,7 +17,7 @@ module Scripting =
 
     let executeProcess fileName arguments =
         let processWriteMessage (chan:TextWriter) (message:string) =
-            if message <> null then 
+            if not (isNull message) then 
                 chan.WriteLine(message) 
         printfn "%s %s" fileName arguments
         let info = ProcessStartInfo(Arguments=arguments, UseShellExecute=false, 
@@ -122,15 +122,15 @@ module Scripting =
             cmdArgs.RedirectOutput|> Option.iter (fun f ->
                 processInfo.RedirectStandardOutput <- true
                 p.OutputDataReceived.Add (fun ea -> 
-                    if ea.Data <> null then 
+                    if not (isNull (ea.Data)) then 
                         out.Append(ea.Data + Environment.NewLine) |> ignore
                         f ea.Data)
             )
 
             cmdArgs.RedirectError |> Option.iter (fun f ->
                 processInfo.RedirectStandardError <- true
                 p.ErrorDataReceived.Add (fun ea -> 
-                    if ea.Data <> null then 
+                    if not (isNull (ea.Data)) then 
                         err.Append(ea.Data + Environment.NewLine) |> ignore
                         f ea.Data)
             )

tests/service/ProjectAnalysisTests.fs

@@ -9,7 +9,7 @@ module Tests.Service.ProjectAnalysisTests
 
 #nowarn "57" // Experimental stuff
 
-let runningOnMono = try System.Type.GetType("Mono.Runtime") <> null with e ->  false
+let runningOnMono = try not (isNull (System.Type.GetType("Mono.Runtime"))) with e ->  false
 
 open NUnit.Framework
 open FsUnit