less allocations

Author: lbargaoanu

src/AutoMapper/Execution/ExpressionBuilder.cs

@@ -33,6 +33,12 @@ public static class ExpressionBuilder
         private static readonly MethodInfo CheckContextMethod = typeof(ResolutionContext).GetStaticMethod(nameof(ResolutionContext.CheckContext));
         private static readonly MethodInfo ContextMapMethod = typeof(ResolutionContext).GetInstanceMethod(nameof(ResolutionContext.MapInternal));
         private static readonly MethodInfo ArrayEmptyMethod = typeof(Array).GetStaticMethod(nameof(Array.Empty));
+        private static readonly ParameterExpression Disposable = Variable(typeof(IDisposable), "disposableEnumerator");
+        private static readonly ParameterExpression[] DisposableArray = new[] { Disposable };
+        private static readonly Expression DisposeCall = IfNullElse(Disposable, Empty, Expression.Call(Disposable, DisposeMethod));
+        private static readonly ParameterExpression Index = Variable(typeof(int), "sourceArrayIndex");
+        private static readonly BinaryExpression ResetIndex = Assign(Index, Zero);
+        private static readonly UnaryExpression IncrementIndex = PostIncrementAssign(Index);
 
         public static Expression MapExpression(this IGlobalConfiguration configurationProvider, ProfileMap profileMap, TypePair typePair, Expression sourceParameter,
             MemberMap propertyMap = null, Expression destinationParameter = null)
@@ -262,13 +268,12 @@ public static Expression ForEach(ParameterExpression loopVar, Expression collect
             static Expression ForEachArrayItem(ParameterExpression loopVar, Expression array, Expression loopContent)
             {
                 var breakLabel = Label("LoopBreak");
-                var index = Variable(typeof(int), "sourceArrayIndex");
-                var loop = Block(new[] { index, loopVar },
-                    Assign(index, Zero),
+                var loop = Block(new[] { Index, loopVar },
+                    ResetIndex,
                     Loop(
                         IfThenElse(
-                            LessThan(index, ArrayLength(array)),
-                            Block(Assign(loopVar, ArrayAccess(array, index)), loopContent, PostIncrementAssign(index)),
+                            LessThan(Index, ArrayLength(array)),
+                            Block(Assign(loopVar, ArrayAccess(array, Index)), loopContent, IncrementIndex),
                             Break(breakLabel)
                         ),
                     breakLabel));
@@ -287,9 +292,8 @@ static Expression Using(Expression disposable, Expression body)
                     {
                         return body;
                     }
-                    var disposableVariable = Variable(typeof(IDisposable), "disposableVariable");
-                    var assignDisposable = Assign(disposableVariable, TypeAs(disposable, typeof(IDisposable)));
-                    disposeCall = Block(new[] { disposableVariable }, assignDisposable, IfNullElse(disposableVariable, Empty, Expression.Call(disposableVariable, DisposeMethod)));
+                    var assignDisposable = Assign(Disposable, TypeAs(disposable, typeof(IDisposable)));
+                    disposeCall = Block(DisposableArray, assignDisposable, DisposeCall);
                 }
                 return TryFinally(body, disposeCall);
             }

src/AutoMapper/Mappers/CollectionMapper.cs

@@ -157,6 +157,9 @@ static class ArrayMapper
             private static readonly MethodInfo CopyToMethod = typeof(Array).GetMethod("CopyTo", new[] { typeof(Array), typeof(int) });
             private static readonly MethodInfo CountMethod = typeof(Enumerable).StaticGenericMethod("Count", parametersCount: 1);
             private static readonly MethodInfo MapMultidimensionalMethod = typeof(ArrayMapper).GetStaticMethod(nameof(MapMultidimensional));
+            private static readonly ParameterExpression Index = Variable(typeof(int), "destinationArrayIndex");
+            private static readonly BinaryExpression ResetIndex = Assign(Index, Zero);
+            private static readonly UnaryExpression IncrementIndex = PostIncrementAssign(Index);
             private static Array MapMultidimensional(Array source, Type destinationElementType, ResolutionContext context)
             {
                 var sourceElementType = source.GetType().GetElementType();
@@ -199,11 +202,10 @@ public static Expression MapToArray(IGlobalConfiguration configurationProvider,
                 }
                 var itemParam = Parameter(sourceElementType, "sourceItem");
                 var itemExpr = configurationProvider.MapExpression(profileMap, new TypePair(sourceElementType, destinationElementType), itemParam);
-                var indexParam = Parameter(typeof(int), "destinationArrayIndex");
-                var setItem = Assign(ArrayAccess(destination, PostIncrementAssign(indexParam)), itemExpr);
-                return Block(new[] { destination, indexParam },
+                var setItem = Assign(ArrayAccess(destination, IncrementIndex), itemExpr);
+                return Block(new[] { destination, Index },
                     createDestination,
-                    Assign(indexParam, Zero),
+                    ResetIndex,
                     ForEach(itemParam, sourceExpression, setItem),
                     destination);
                 Expression MapFromArray()