Reduced allocation by reading from a stream into an array for ILResource (#4689) (#4721)

* Reduced allocation by reading from a stream into an array for ILResource

* GetRawFSharpSignatureData is now lazy getting bytes. This is what GetRawFSharpOptimizationData does

* Using File.ReadBinaryChunk

src/absil/il.fs

@@ -8,6 +8,7 @@ module Microsoft.FSharp.Compiler.AbstractIL.IL
 
 
 open System
+open System.IO
 open System.Collections
 open System.Collections.Generic
 open System.Collections.Concurrent
@@ -1986,7 +1987,7 @@ type ILResource =
     member r.GetBytes() = 
         match r.Location with
         | ILResourceLocation.LocalIn (file, start, len) -> 
-            FileSystem.ReadAllBytesShim(file).[start .. start + len - 1]
+            File.ReadBinaryChunk(file, start, len)
         | ILResourceLocation.LocalOut bytes -> bytes
         | _ -> failwith "GetBytes"
 

src/absil/illib.fs

@@ -1291,7 +1291,7 @@ module Shim =
         static member ReadBinaryChunk (fileName, start, len) = 
             use stream = FileSystem.FileStreamReadShim fileName
             stream.Seek(int64 start, SeekOrigin.Begin) |> ignore
-            let buffer = Array.zeroCreate  len 
+            let buffer = Array.zeroCreate len 
             let mutable n = 0
             while n < len do 
                 n <- n + stream.Read(buffer, n, len-n)

src/fsharp/CompileOps.fs

@@ -2098,7 +2098,7 @@ type IRawFSharpAssemblyData =
     /// in the language service
     abstract TryGetILModuleDef : unit -> ILModuleDef option
     ///  The raw F# signature data in the assembly, if any
-    abstract GetRawFSharpSignatureData : range * ilShortAssemName: string * fileName: string -> (string * byte[]) list
+    abstract GetRawFSharpSignatureData : range * ilShortAssemName: string * fileName: string -> (string * (unit -> byte[])) list
     ///  The raw F# optimization data in the assembly, if any
     abstract GetRawFSharpOptimizationData : range * ilShortAssemName: string * fileName: string -> (string * (unit -> byte[])) list
     ///  The table of type forwarders in the assembly
@@ -3795,7 +3795,7 @@ let PickleToResource inMem file g scope rname p x =
       MetadataIndex = NoMetadataIdx }
 
 let GetSignatureData (file, ilScopeRef, ilModule, byteReader) : PickledDataWithReferences<PickledCcuInfo> = 
-    unpickleObjWithDanglingCcus file ilScopeRef ilModule unpickleCcuInfo byteReader
+    unpickleObjWithDanglingCcus file ilScopeRef ilModule unpickleCcuInfo (byteReader())
 
 let WriteSignatureData (tcConfig: TcConfig, tcGlobals, exportRemapping, ccu: CcuThunk, file, inMem) : ILResource = 
     let mspec = ccu.Contents
@@ -3831,16 +3831,15 @@ type RawFSharpAssemblyDataBackedByFileOnDisk (ilModule: ILModuleDef, ilAssemblyR
             let sigDataReaders = 
                 [ for iresource in resources do
                     if IsSignatureDataResource iresource then 
-                        let ccuName = GetSignatureDataResourceName iresource 
-                        let bytes = iresource.GetBytes()
-                        yield (ccuName, bytes) ]
+                        let ccuName = GetSignatureDataResourceName iresource
+                        yield (ccuName, fun () -> iresource.GetBytes()) ]
                         
             let sigDataReaders = 
                 if sigDataReaders.IsEmpty && List.contains ilShortAssemName externalSigAndOptData then 
                     let sigFileName = Path.ChangeExtension(filename, "sigdata")
                     if not (FileSystem.SafeExists sigFileName) then 
                         error(Error(FSComp.SR.buildExpectedSigdataFile (FileSystem.GetFullPathShim sigFileName), m))
-                    [ (ilShortAssemName, FileSystem.ReadAllBytesShim sigFileName)]
+                    [ (ilShortAssemName, fun () -> FileSystem.ReadAllBytesShim sigFileName)]
                 else
                     sigDataReaders
             sigDataReaders

src/fsharp/CompileOps.fsi

@@ -149,7 +149,7 @@ type IRawFSharpAssemblyData =
     abstract HasAnyFSharpSignatureDataAttribute: bool
     abstract HasMatchingFSharpSignatureDataAttribute: ILGlobals -> bool
     ///  The raw F# signature data in the assembly, if any
-    abstract GetRawFSharpSignatureData: range * ilShortAssemName: string * fileName: string -> (string * byte[]) list
+    abstract GetRawFSharpSignatureData: range * ilShortAssemName: string * fileName: string -> (string * (unit -> byte[])) list
     ///  The raw F# optimization data in the assembly, if any
     abstract GetRawFSharpOptimizationData: range * ilShortAssemName: string * fileName: string -> (string * (unit -> byte[])) list
     ///  The table of type forwarders in the assembly

src/fsharp/service/IncrementalBuild.fs

@@ -1172,8 +1172,7 @@ type RawFSharpAssemblyDataBackedByLanguageService (tcConfig, tcGlobals, tcState:
         let _sigDataAttributes, sigDataResources = Driver.EncodeInterfaceData(tcConfig, tcGlobals, exportRemapping, generatedCcu, outfile, true)
         [ for r in sigDataResources  do
             let ccuName = GetSignatureDataResourceName r
-            let bytes = r.GetBytes()
-            yield (ccuName, bytes) ]
+            yield (ccuName, (fun () -> r.GetBytes())) ]
 
     let autoOpenAttrs = topAttrs.assemblyAttrs |> List.choose (List.singleton >> TryFindFSharpStringAttribute tcGlobals tcGlobals.attrib_AutoOpenAttribute)
     let ivtAttrs = topAttrs.assemblyAttrs |> List.choose (List.singleton >> TryFindFSharpStringAttribute tcGlobals tcGlobals.attrib_InternalsVisibleToAttribute)