Use the known length int constructor if available when lowering colle…

…ction expressions
dotnet · Mar 6, 2024 · 05c5f8e · 05c5f8e
1 parent 8915842
commit 05c5f8e
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Showing 6 changed files with 770 additions and 841 deletions.
diff --git a/src/Compilers/CSharp/Portable/Lowering/LocalRewriter/LocalRewriter_CollectionExpression.cs b/src/Compilers/CSharp/Portable/Lowering/LocalRewriter/LocalRewriter_CollectionExpression.cs
@@ -867,24 +867,22 @@ private BoundExpression CreateAndPopulateList(BoundCollectionExpression node, Ty
             bool useKnownLength = ShouldUseKnownLength(node, out numberIncludingLastSpread);
             RewriteCollectionExpressionElementsIntoTemporaries(elements, numberIncludingLastSpread, localsBuilder, sideEffects);
 
-            bool useOptimizations = false;
-            MethodSymbol? setCount = null;
+            bool useOptimization = false;
             MethodSymbol? asSpan = null;
 
-            // Do not use optimizations in async method since the optimizations require Span<T>.
+            // Do not use optimization in async method since the optimization require Span<T>.
             if (useKnownLength && elements.Length > 0 && _factory.CurrentFunction?.IsAsync == false)
             {
-                setCount = ((MethodSymbol?)_compilation.GetWellKnownTypeMember(WellKnownMember.System_Runtime_InteropServices_CollectionsMarshal__SetCount_T))?.Construct(typeArguments);
                 asSpan = ((MethodSymbol?)_compilation.GetWellKnownTypeMember(WellKnownMember.System_Runtime_InteropServices_CollectionsMarshal__AsSpan_T))?.Construct(typeArguments);
 
-                if (setCount is { } && asSpan is { })
+                if (asSpan is { })
                 {
-                    useOptimizations = true;
+                    useOptimization = true;
                 }
             }
 
             BoundObjectCreationExpression rewrittenReceiver;
-            if (useKnownLength && elements.Length > 0 && !useOptimizations)
+            if (useKnownLength && elements.Length > 0)
             {
                 // List<ElementType> list = new(N + s1.Length + ...);
                 var constructor = ((MethodSymbol)_factory.WellKnownMember(WellKnownMember.System_Collections_Generic_List_T__ctorInt32)).AsMember(collectionType);
@@ -903,16 +901,11 @@ private BoundExpression CreateAndPopulateList(BoundCollectionExpression node, Ty
             localsBuilder.Add(listTemp);
             sideEffects.Add(assignmentToTemp);
 
-            // Use Span<T> if CollectionsMarshal methods are available, otherwise use List<T>.Add().
-            if (useOptimizations)
+            // Use Span<T> if CollectionsMarshal.AsSpan is available, otherwise use List<T>.Add().
+            if (useOptimization)
             {
-                Debug.Assert(useKnownLength);
-                Debug.Assert(setCount is { });
                 Debug.Assert(asSpan is { });
 
-                // CollectionsMarshal.SetCount<ElementType>(list, N + s1.Length + ...);
-                sideEffects.Add(_factory.Call(receiver: null, setCount, listTemp, GetKnownLengthExpression(elements, numberIncludingLastSpread, localsBuilder)));
-
                 // var span = CollectionsMarshal.AsSpan<ElementType(list);
                 BoundLocal spanTemp = _factory.StoreToTemp(_factory.Call(receiver: null, asSpan, listTemp), out assignmentToTemp, isKnownToReferToTempIfReferenceType: true);
                 localsBuilder.Add(spanTemp);