SIMD vectorization of Array.sum<int>, etc

src/FSharp.Core/array.fs

@@ -1578,19 +1578,38 @@ 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>
 
         for i = 0 to array.Length - 1 do
             acc <- Checked.(+) acc array.[i]
 
         acc
-        when ^T : float = (System.Linq.Enumerable.Sum : IEnumerable<float> -> float) (# "" array : IEnumerable<float> #)
-        when ^T : float32 = (System.Linq.Enumerable.Sum : IEnumerable<float32> -> float32) (# "" array : IEnumerable<float32> #)
-        when ^T : int = (System.Linq.Enumerable.Sum : IEnumerable<int> -> int) (# "" array : IEnumerable<int> #)
-        when ^T : int64 = (System.Linq.Enumerable.Sum : IEnumerable<int64> -> int64) (# "" array : IEnumerable<int64> #)
+
+    [<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 =

src/FSharp.Core/seq.fs

@@ -1464,19 +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 
-        when ^a: int64 = (System.Linq.Enumerable.Sum: IEnumerable<int64> -> int64) (# "" source : IEnumerable<int64> #) 
-        when ^a: int = (System.Linq.Enumerable.Sum: IEnumerable<int> -> int) (# "" source : IEnumerable<int> #) 
-        when ^a: float32 = (System.Linq.Enumerable.Sum: IEnumerable<float32> -> float32) (# "" source : IEnumerable<float32> #) 
-        when ^a: float = (System.Linq.Enumerable.Sum: IEnumerable<float> -> float) (# "" source : IEnumerable<float> #)
+
+    [<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 =