IL: use empty tables for members when possible

docs/release-notes/.FSharp.Compiler.Service/11.0.100.md

@@ -163,6 +163,7 @@
 * Expand `<inheritdoc/>` at tooling time. In IDE tooltips, completion, and signature help, documentation is inherited from base classes, interfaces, overridden members, and constructors (matched by parameter signature). The FCS Symbols API (`FSharpSymbol.XmlDoc`) additionally resolves explicit `cref` targets, but does not expand constructor inheritance. The compiler emits the tag verbatim into generated XML documentation files, matching C#; `<include>` is not implemented. ([Issue #19175](https://github.com/dotnet/fsharp/issues/19175), [PR #19188](https://github.com/dotnet/fsharp/pull/19188))
 * Add symbol and type highlighting to F# diagnostics ([PR #20097](https://github.com/dotnet/fsharp/pull/20097))
 * IL: add `ILPreNamespace`, make `ILPreTypeDef` creation lazy ([PR #20092](https://github.com/dotnet/fsharp/pull/20092))
+* IL: use empty tables for members when possible ([PR #20249](https://github.com/dotnet/fsharp/pull/20249))
 
 ### Improved
 

src/Compiler/AbstractIL/ilread.fs

@@ -1542,6 +1542,26 @@ let seekReadMethodImplRow (ctxt: ILMetadataReader) mdv idx =
     let mdeclIdx = seekReadMethodDefOrRefIdx ctxt mdv &addr
     (tidx, mbodyIdx, mdeclIdx)
 
+/// Rows of a table keyed by type def in its first column: at most one per type in EventMap and
+/// PropertyMap, pointing at its member range, and the overrides themselves in MethodImpl. Called per
+/// type def rather than when the table it feeds is forced, so the types with no rows - most of them -
+/// can share the empty table.
+let seekReadRowRangeForTypeDef (ctxt: ILMetadataReader) mdv (table: TableName) tidx =
+    let searcher =
+        { new ISeekReadIndexedRowReader<int, int, int> with
+            member _.GetRow(i, rowIndex) = rowIndex <- i
+            member _.GetKey(rowIndex) = rowIndex
+
+            member _.CompareKey(rowIndex) =
+                let mutable addr = ctxt.rowAddr table rowIndex
+                let rowTidx = seekReadUntaggedIdx TableNames.TypeDef ctxt mdv &addr
+                simpleIndexCompare tidx rowTidx
+
+            member _.ConvertRow(rowIndex) = rowIndex
+        }
+
+    seekReadIndexedRowsRange (ctxt.getNumRows table) true searcher
+
 /// Read Table ILModuleRef.
 let seekReadModuleRefRow (ctxt: ILMetadataReader) mdv idx =
     let mutable addr = ctxt.rowAddr TableNames.ModuleRef idx
@@ -2192,9 +2212,9 @@ and typeDefReader ctxtH : ILTypeDefStored =
 
         let impls = seekReadInterfaceImpls ctxt mdv numTypars idx
 
-        let mimpls = seekReadMethodImpls ctxt numTypars idx
-        let props = seekReadProperties ctxt numTypars idx
-        let events = seekReadEvents ctxt numTypars idx
+        let mimpls = seekReadMethodImpls ctxt mdv numTypars idx
+        let props = seekReadProperties ctxt mdv numTypars idx
+        let events = seekReadEvents ctxt mdv numTypars idx
 
         ILTypeDef(
             name = nm,
@@ -2544,26 +2564,30 @@ and seekReadField ctxt mdv (numTypars, hasLayout) (idx: int) =
     )
 
 and seekReadFields (ctxt: ILMetadataReader) (numTypars, hasLayout) fidx1 fidx2 =
-    mkILFieldsLazy (
-        InterruptibleLazy(fun _ ->
-            let mdv = ctxt.mdfile.GetView()
+    if fidx1 <= 0 || fidx2 <= fidx1 then
+        emptyILFields
+    else
+        mkILFieldsLazy (
+            InterruptibleLazy(fun _ ->
+                let mdv = ctxt.mdfile.GetView()
 
-            [
-                if fidx1 > 0 then
+                [
                     for i = fidx1 to fidx2 - 1 do
                         yield seekReadField ctxt mdv (numTypars, hasLayout) i
-            ])
-    )
+                ])
+        )
 
 and seekReadMethods (ctxt: ILMetadataReader) numTypars midx1 midx2 =
-    mkILMethodsComputed (fun () ->
-        let mdv = ctxt.mdfile.GetView()
+    if midx1 <= 0 || midx2 <= midx1 then
+        emptyILMethods
+    else
+        mkILMethodsComputed (fun () ->
+            let mdv = ctxt.mdfile.GetView()
 
-        [|
-            if midx1 > 0 then
+            [|
                 for i = midx1 to midx2 - 1 do
                     yield seekReadMethod ctxt mdv numTypars i
-        |])
+            |])
 
 and sigptrGetTypeDefOrRefOrSpecIdx bytes sigptr =
     let struct (n, sigptr) = sigptrGetZInt32 bytes sigptr
@@ -3110,40 +3134,37 @@ and seekReadParamExtras (ctxt: ILMetadataReader) mdv (retRes: byref<ILReturn>, p
                 MetadataIndex = idx
             }
 
-and seekReadMethodImpls (ctxt: ILMetadataReader) numTypars tidx =
-    mkILMethodImplsLazy (
-        lazy
-            let mdv = ctxt.mdfile.GetView()
+and seekReadMethodImpls (ctxt: ILMetadataReader) mdv numTypars tidx =
+    let startIdx, endIdx =
+        seekReadRowRangeForTypeDef ctxt mdv TableNames.MethodImpl tidx
 
-            let mimpls =
-                seekReadIndexedRows (
-                    ctxt.getNumRows TableNames.MethodImpl,
-                    id,
-                    id,
-                    (fun i ->
-                        let mutable addr = ctxt.rowAddr TableNames.MethodImpl i
-                        let _tidx = seekReadUntaggedIdx TableNames.TypeDef ctxt mdv &addr
-                        simpleIndexCompare tidx _tidx),
-                    isSorted ctxt TableNames.MethodImpl,
-                    seekReadMethodImplRow ctxt mdv
-                )
+    if startIdx <= 0 || endIdx < startIdx then
+        emptyILMethodImpls
+    else
+        mkILMethodImplsLazy (
+            lazy
+                let mdv = ctxt.mdfile.GetView()
 
-            mimpls
-            |> List.map (fun (_, b, c) ->
-                {
-                    OverrideBy =
-                        let (MethodData(enclTy, cc, nm, argTys, retTy, methInst)) =
-                            seekReadMethodDefOrRefNoVarargs ctxt numTypars b
+                [
+                    for i in startIdx..endIdx do
+                        let _, b, c = seekReadMethodImplRow ctxt mdv i
+
+                        yield
+                            {
+                                OverrideBy =
+                                    let (MethodData(enclTy, cc, nm, argTys, retTy, methInst)) =
+                                        seekReadMethodDefOrRefNoVarargs ctxt numTypars b
 
-                        mkILMethSpecInTy (enclTy, cc, nm, argTys, retTy, methInst)
-                    Overrides =
-                        let (MethodData(enclTy, cc, nm, argTys, retTy, methInst)) =
-                            seekReadMethodDefOrRefNoVarargs ctxt numTypars c
+                                    mkILMethSpecInTy (enclTy, cc, nm, argTys, retTy, methInst)
+                                Overrides =
+                                    let (MethodData(enclTy, cc, nm, argTys, retTy, methInst)) =
+                                        seekReadMethodDefOrRefNoVarargs ctxt numTypars c
 
-                        let mspec = mkILMethSpecInTy (enclTy, cc, nm, argTys, retTy, methInst)
-                        OverridesSpec(mspec.MethodRef, mspec.DeclaringType)
-                })
-    )
+                                    let mspec = mkILMethSpecInTy (enclTy, cc, nm, argTys, retTy, methInst)
+                                    OverridesSpec(mspec.MethodRef, mspec.DeclaringType)
+                            }
+                ]
+        )
 
 and seekReadMultipleMethodSemantics (ctxt: ILMetadataReader) (flags, id) =
     seekReadIndexedRows (
@@ -3189,27 +3210,17 @@ and seekReadEvent ctxt mdv numTypars idx =
         metadataIndex = idx
     )
 
-(* REVIEW: can substantially reduce numbers of EventMap and PropertyMap reads by first checking if the whole table mdv sorted according to ILTypeDef tokens and then doing a binary chop *)
-and seekReadEvents (ctxt: ILMetadataReader) numTypars tidx =
-    mkILEventsLazy (
-        InterruptibleLazy(fun _ ->
-            let mdv = ctxt.mdfile.GetView()
+and seekReadEvents (ctxt: ILMetadataReader) mdv numTypars tidx =
+    let rowNum, _ = seekReadRowRangeForTypeDef ctxt mdv TableNames.EventMap tidx
+
+    if rowNum <= 0 then
+        emptyILEvents
+    else
+        mkILEventsLazy (
+            InterruptibleLazy(fun _ ->
+                let mdv = ctxt.mdfile.GetView()
+                let _, beginEventIdx = seekReadEventMapRow ctxt mdv rowNum
 
-            match
-                seekReadOptionalIndexedRow (
-                    ctxt.getNumRows TableNames.EventMap,
-                    id,
-                    id,
-                    (fun i ->
-                        let mutable addr = ctxt.rowAddr TableNames.EventMap i
-                        let _tidx = seekReadUntaggedIdx TableNames.TypeDef ctxt mdv &addr
-                        simpleIndexCompare tidx _tidx),
-                    false,
-                    (fun i -> i, seekReadEventMapRow ctxt mdv i |> snd)
-                )
-            with
-            | None -> []
-            | Some(rowNum, beginEventIdx) ->
                 let endEventIdx =
                     if rowNum >= ctxt.getNumRows TableNames.EventMap then
                         ctxt.getNumRows TableNames.Event + 1
@@ -3222,7 +3233,7 @@ and seekReadEvents (ctxt: ILMetadataReader) numTypars tidx =
                         for i in beginEventIdx .. endEventIdx - 1 do
                             yield seekReadEvent ctxt mdv numTypars i
                 ])
-    )
+        )
 
 and seekReadProperty ctxt mdv numTypars idx =
     let flags, nameIdx, typIdx = seekReadPropertyRow ctxt mdv idx
@@ -3260,26 +3271,17 @@ and seekReadProperty ctxt mdv numTypars idx =
         metadataIndex = idx
     )
 
-and seekReadProperties (ctxt: ILMetadataReader) numTypars tidx =
-    mkILPropertiesLazy (
-        InterruptibleLazy(fun _ ->
-            let mdv = ctxt.mdfile.GetView()
+and seekReadProperties (ctxt: ILMetadataReader) mdv numTypars tidx =
+    let rowNum, _ = seekReadRowRangeForTypeDef ctxt mdv TableNames.PropertyMap tidx
+
+    if rowNum <= 0 then
+        emptyILProperties
+    else
+        mkILPropertiesLazy (
+            InterruptibleLazy(fun _ ->
+                let mdv = ctxt.mdfile.GetView()
+                let _, beginPropIdx = seekReadPropertyMapRow ctxt mdv rowNum
 
-            match
-                seekReadOptionalIndexedRow (
-                    ctxt.getNumRows TableNames.PropertyMap,
-                    id,
-                    id,
-                    (fun i ->
-                        let mutable addr = ctxt.rowAddr TableNames.PropertyMap i
-                        let _tidx = seekReadUntaggedIdx TableNames.TypeDef ctxt mdv &addr
-                        simpleIndexCompare tidx _tidx),
-                    false,
-                    (fun i -> i, seekReadPropertyMapRow ctxt mdv i |> snd)
-                )
-            with
-            | None -> []
-            | Some(rowNum, beginPropIdx) ->
                 let endPropIdx =
                     if rowNum >= ctxt.getNumRows TableNames.PropertyMap then
                         ctxt.getNumRows TableNames.Property + 1
@@ -3292,7 +3294,7 @@ and seekReadProperties (ctxt: ILMetadataReader) numTypars tidx =
                         for i in beginPropIdx .. endPropIdx - 1 do
                             yield seekReadProperty ctxt mdv numTypars i
                 ])
-    )
+        )
 
 and customAttrsReaderFn ctxtH tag : int32 -> ILAttribute[] =
     fun idx ->