SIMD vectorization of Array.sum<int>, etc

docs/release-notes/.FSharp.Core/9.0.300.md

@@ -6,6 +6,7 @@
 * Support for `and!` in `TaskBuilder` ([LanguageSuggestion #1363](https://github.com/fsharp/fslang-suggestions/issues/1363), [PR #18451](https://github.com/dotnet/fsharp/pull/18451))
 
 ### Changed
+* Array.sum and Seq.sum to call System.Linq.Enumerable methods on base-types (float/float32/int/int64) to utilize vectorization. [PR #18509](https://github.com/dotnet/fsharp/pull/18509)
 
 ### Breaking Changes
 * Struct unions with overlapping fields now generate mappings needed for reading via reflection ([Issue #18121](https://github.com/dotnet/fsharp/issues/17797), [PR #18274](https://github.com/dotnet/fsharp/pull/18274)). Previous versions of FSharp.Core returned incomplete mapping between fields and cases, these older fslib versions will now report an exception.

src/FSharp.Core/array.fs

@@ -1578,8 +1578,7 @@ module Array =
         checkNonNull "array" array
         Microsoft.FSharp.Primitives.Basics.Array.permute indexMap array
 
-    [<CompiledName("Sum")>]
-    let inline sum (array: ^T array) : ^T =
+    let inline private classicSum (array: ^T array) : ^T =
         checkNonNull "array" array
         let mutable acc = LanguagePrimitives.GenericZero< ^T>
 
@@ -1588,6 +1587,30 @@ module Array =
 
         acc
 
+    [<CompiledName("Sum")>]
+    let inline sum (array: ^T array) : ^T =
+        classicSum array
+        when ^T : float = 
+            if System.Runtime.InteropServices.RuntimeInformation.FrameworkDescription.StartsWith ".NET Framework" then classicSum array
+            else 
+                let r = (System.Linq.Enumerable.Sum : IEnumerable<float> -> float) (# "" array : IEnumerable<float> #)
+                (# "" r : 'T #)
+        when ^T : float32 = 
+            if System.Runtime.InteropServices.RuntimeInformation.FrameworkDescription.StartsWith ".NET Framework" then classicSum array
+            else 
+                let r = (System.Linq.Enumerable.Sum : IEnumerable<float32> -> float32) (# "" array : IEnumerable<float32> #)
+                (# "" r : 'T #)
+        when ^T : int = 
+            if System.Runtime.InteropServices.RuntimeInformation.FrameworkDescription.StartsWith ".NET Framework" then classicSum array
+            else 
+                let r = (System.Linq.Enumerable.Sum : IEnumerable<int> -> int) (# "" array : IEnumerable<int> #)
+                (# "" r : 'T #)
+        when ^T : int64 = 
+            if System.Runtime.InteropServices.RuntimeInformation.FrameworkDescription.StartsWith ".NET Framework" then classicSum array
+            else 
+                let r = (System.Linq.Enumerable.Sum : IEnumerable<int64> -> int64) (# "" array : IEnumerable<int64> #)
+                (# "" r : 'T #)
+
     [<CompiledName("SumBy")>]
     let inline sumBy ([<InlineIfLambda>] projection: 'T -> ^U) (array: 'T array) : ^U =
         checkNonNull "array" array

src/FSharp.Core/seq.fs

@@ -478,7 +478,8 @@ module Internal =
             static member Bind(g: Generator<'T>, cont) =
                 match g with
                 | :? GenerateThen<'T> as g ->
-                    GenerateThen<_>.Bind(g.Generator, (fun () -> GenerateThen<_>.Bind(g.Cont(), cont)))
+                    GenerateThen<_>
+                        .Bind(g.Generator, (fun () -> GenerateThen<_>.Bind(g.Cont(), cont)))
                 | g -> (new GenerateThen<'T>(g, cont) :> Generator<'T>)
 
         let bindG g cont =
@@ -1463,15 +1464,38 @@ module Seq =
         else
             mkDelayedSeq (fun () -> countByRefType projection source)
 
-    [<CompiledName("Sum")>]
-    let inline sum (source: seq< ^a >) : ^a =
+    let inline private classicSum (source: seq< ^a >) : ^a =
         use e = source.GetEnumerator()
         let mutable acc = LanguagePrimitives.GenericZero< ^a>
 
         while e.MoveNext() do
             acc <- Checked.(+) acc e.Current
 
-        acc
+        acc 
+
+    [<CompiledName("Sum")>]
+    let inline sum (source: seq< ^a >) : ^a =
+        classicSum source
+        when ^a: int64 = 
+            if System.Runtime.InteropServices.RuntimeInformation.FrameworkDescription.StartsWith ".NET Framework" then classicSum source
+            else 
+                let r = (System.Linq.Enumerable.Sum: IEnumerable<int64> -> int64) (# "" source : IEnumerable<int64> #)
+                (# "" r : 'a #)
+        when ^a: int = 
+            if System.Runtime.InteropServices.RuntimeInformation.FrameworkDescription.StartsWith ".NET Framework" then classicSum source
+            else
+                let r = (System.Linq.Enumerable.Sum: IEnumerable<int> -> int) (# "" source : IEnumerable<int> #)
+                (# "" r : 'a #)
+        when ^a: float32 = 
+            if System.Runtime.InteropServices.RuntimeInformation.FrameworkDescription.StartsWith ".NET Framework" then classicSum source
+            else 
+                let r = (System.Linq.Enumerable.Sum: IEnumerable<float32> -> float32) (# "" source : IEnumerable<float32> #)
+                (# "" r : 'a #)
+        when ^a: float = 
+            if System.Runtime.InteropServices.RuntimeInformation.FrameworkDescription.StartsWith ".NET Framework" then classicSum source
+            else
+                let r = (System.Linq.Enumerable.Sum: IEnumerable<float> -> float) (# "" source : IEnumerable<float> #)
+                (# "" r : 'a #)
 
     [<CompiledName("SumBy")>]
     let inline sumBy ([<InlineIfLambda>] projection: 'T -> ^U) (source: seq<'T>) : ^U =

tests/benchmarks/CompiledCodeBenchmarks/MicroPerf/Collections.fs

@@ -141,6 +141,11 @@ type CollectionsBenchmark() =
         |> Array.updateAt (x.Length - 1) 1
         |> ignore
 
+    [<Benchmark>]
+    member x.ArraySum() =
+        array
+        |> Array.sum 
+        |> ignore
     /// Seq
     [<Benchmark>]
     member x.SeqBaseline() =