Add LowerIntegralRangesToFastLoops lang feature

Author: brianrourkeboll

docs/release-notes/.Language/preview.md

@@ -1,5 +1,6 @@
 ### Added
 
+* Lower integral ranges to fast loops in more cases and optimize list and array construction from ranges. ([PR #16650](https://github.com/dotnet/fsharp/pull/16650))
 * Better generic unmanaged structs handling. ([Language suggestion #692](https://github.com/fsharp/fslang-suggestions/issues/692), [PR #12154](https://github.com/dotnet/fsharp/pull/12154))
 * Bidirectional F#/C# interop for 'unmanaged' constraint. ([PR #12154](https://github.com/dotnet/fsharp/pull/12154))
 * Make `.Is*` discriminated union properties visible. ([Language suggestion #222](https://github.com/fsharp/fslang-suggestions/issues/222), [PR #16341](https://github.com/dotnet/fsharp/pull/16341))

src/Compiler/FSComp.txt

@@ -1594,6 +1594,7 @@ featureWarningIndexedPropertiesGetSetSameType,"Indexed properties getter and set
 featureChkTailCallAttrOnNonRec,"Raises warnings if the 'TailCall' attribute is used on non-recursive functions."
 featureUnionIsPropertiesVisible,"Union case test properties"
 featureBooleanReturningAndReturnTypeDirectedPartialActivePattern,"Boolean-returning and return-type-directed partial active patterns"
+featureLowerIntegralRangesToFastLoops,"Optimizes certain uses of the integral range (..) and range-step (.. ..) operators to fast while-loops."
 3354,tcNotAFunctionButIndexerNamedIndexingNotYetEnabled,"This value supports indexing, e.g. '%s.[index]'. The syntax '%s[index]' requires /langversion:preview. See https://aka.ms/fsharp-index-notation."
 3354,tcNotAFunctionButIndexerIndexingNotYetEnabled,"This expression supports indexing, e.g. 'expr.[index]'. The syntax 'expr[index]' requires /langversion:preview. See https://aka.ms/fsharp-index-notation."
 3355,tcNotAnIndexerNamedIndexingNotYetEnabled,"The value '%s' is not a function and does not support index notation."

src/Compiler/Facilities/LanguageFeatures.fs

@@ -85,6 +85,7 @@ type LanguageFeature =
     | WarningIndexedPropertiesGetSetSameType
     | WarningWhenTailCallAttrOnNonRec
     | BooleanReturningAndReturnTypeDirectedPartialActivePattern
+    | LowerIntegralRangesToFastLoops
 
 /// LanguageVersion management
 type LanguageVersion(versionText) =
@@ -197,6 +198,7 @@ type LanguageVersion(versionText) =
                 LanguageFeature.WarningWhenTailCallAttrOnNonRec, previewVersion
                 LanguageFeature.UnionIsPropertiesVisible, previewVersion
                 LanguageFeature.BooleanReturningAndReturnTypeDirectedPartialActivePattern, previewVersion
+                LanguageFeature.LowerIntegralRangesToFastLoops, previewVersion
             ]
 
     static let defaultLanguageVersion = LanguageVersion("default")
@@ -340,6 +342,7 @@ type LanguageVersion(versionText) =
         | LanguageFeature.WarningWhenTailCallAttrOnNonRec -> FSComp.SR.featureChkTailCallAttrOnNonRec ()
         | LanguageFeature.BooleanReturningAndReturnTypeDirectedPartialActivePattern ->
             FSComp.SR.featureBooleanReturningAndReturnTypeDirectedPartialActivePattern ()
+        | LanguageFeature.LowerIntegralRangesToFastLoops -> FSComp.SR.featureLowerIntegralRangesToFastLoops ()
 
     /// Get a version string associated with the given feature.
     static member GetFeatureVersionString feature =

src/Compiler/Facilities/LanguageFeatures.fsi

@@ -76,6 +76,7 @@ type LanguageFeature =
     | WarningIndexedPropertiesGetSetSameType
     | WarningWhenTailCallAttrOnNonRec
     | BooleanReturningAndReturnTypeDirectedPartialActivePattern
+    | LowerIntegralRangesToFastLoops
 
 /// LanguageVersion management
 type LanguageVersion =

src/Compiler/Optimize/LowerComputedCollections.fs

@@ -5,6 +5,7 @@ module internal FSharp.Compiler.LowerComputedCollectionExpressions
 open FSharp.Compiler.AbstractIL.IL
 open FSharp.Compiler.AccessibilityLogic
 open FSharp.Compiler.DiagnosticsLogger
+open FSharp.Compiler.Features
 open FSharp.Compiler.InfoReader
 open FSharp.Compiler.LowerSequenceExpressions
 open FSharp.Compiler.MethodCalls
@@ -389,7 +390,7 @@ let LowerComputedListOrArrayExpr tcVal (g: TcGlobals) amap overallExpr =
             match overallSeqExpr with
             // [start..finish]
             // [start..step..finish]
-            | IntegralRange g (_, (start, step, finish)) ->
+            | IntegralRange g (_, (start, step, finish)) when g.langVersion.SupportsFeature LanguageFeature.LowerIntegralRangesToFastLoops ->
                 Some (List.mkFromIntegralRange tcVal g amap m overallElemTy overallSeqExpr start step finish)
 
             // [(* Anything more complex. *)]
@@ -402,7 +403,7 @@ let LowerComputedListOrArrayExpr tcVal (g: TcGlobals) amap overallExpr =
             match overallSeqExpr with
             // [|start..finish|]
             // [|start..step..finish|]
-            | IntegralRange g (_, (start, step, finish)) ->
+            | IntegralRange g (_, (start, step, finish)) when g.langVersion.SupportsFeature LanguageFeature.LowerIntegralRangesToFastLoops ->
                 Some (Array.mkFromIntegralRange g m overallElemTy overallSeqExpr start step finish)
 
             // [|(* Anything more complex. *)|]

src/Compiler/TypedTree/TypedTreeOps.fs

@@ -10694,7 +10694,9 @@ let DetectAndOptimizeForEachExpression g option expr =
            let spFor = match spFor with DebugPointAtBinding.Yes mFor -> DebugPointAtFor.Yes mFor | _ -> DebugPointAtFor.No
            mkFastForLoop g (spFor, spIn, mWholeExpr, elemVar, startExpr, (step = 1), finishExpr, bodyExpr)
 
-    | OptimizeAllForExpressions, CompiledForEachExpr g (_enumTy, rangeExpr & IntegralRange g (rangeTy, (start, step, finish)), elemVar, bodyExpr, ranges) ->
+    | OptimizeAllForExpressions, CompiledForEachExpr g (_enumTy, rangeExpr & IntegralRange g (rangeTy, (start, step, finish)), elemVar, bodyExpr, ranges) when
+        g.langVersion.SupportsFeature LanguageFeature.LowerIntegralRangesToFastLoops
+        ->
         let mBody, _spFor, _spIn, mFor, mIn, spInWhile, _mWhole = ranges
 
         mkOptimizedRangeLoop