On the Importance of Inlining

inlining.cs

    [Test]
    public static void Inlining()
    {
        var length = 1000;

        // Our Two Lambdas 
        Func<int, bool> Lt5 = x => x < 5;
        Func<int, int, int> AddInts = (x, y) => x + y;

        // Original expression
        var r = length.Range().Where(Lt5).Aggregate(0, AddInts);

        // Expansion 1 (Intermediate variable assignment)
        {
            var x0 = length.Range();
            var x1 = x0.Where(Lt5);
            var x2 = x1.Aggregate(0, AddInts);
            Assert.AreEqual(x2, r);
        }

        // Expansion 2 (Inline function)
        {
            var x0 = new RangeSequence(0, 1000);
            var x1 = x0.Iterator.Where(Lt5).ToSequence();
            var x2 = x1.Iterator.Aggregate(0, AddInts);
            Assert.AreEqual(x2, r);
        }

        // Expansion 3 (Intermediate variable assignment #2)
        {
            var x0 = new RangeSequence(0, 1000);
            var x1 = x0.Iterator;
            var x2 = x1.Where(Lt5);
            var x3 = x2.ToSequence();
            var x4 = x3.Iterator;
            var x5 = x4.Aggregate(0, AddInts);
            Assert.AreEqual(x5, r);
        }


        // Expansion 4: Inline Aggregate
        {
            var x0 = new RangeSequence(0, 1000);
            var x1 = x0.Iterator;
            var x2 = x1.Where(Lt5);
            var x3 = x2.ToSequence();
            var x4 = x3.Iterator;
            var init = 0;
            while (x4.HasValue)
            {
                init = AddInts(init, x4.Value);
                x4= x4.Next;
            }
            Assert.AreEqual(init, r);
        }

        // Expansion 5: Coalescing some null operations.(x = this), inlining more functions
        {
            var x0 = new RangeSequence(0, 1000);
            var x1 = new WhereIterator<int>(x0, Lt5); 
            var init = 0;
            while (x1.HasValue)
            {
                init = AddInts(init, x1.Value);
                x1 = new WhereIterator<int>(x1.Source.Next, Lt5);
            }
            Assert.AreEqual(init, r);
        }

        // Expansion 6: Expanding WhereIterator to local variables 
        // NOTE: this step requires casting to work properly. 
        {
            var x1_Source = new RangeSequence(0, 1000);
            var x1_Predicate = Lt5;
            while (x1_Source.HasValue && !x1_Predicate(x1_Source.Value))
            {
                x1_Source = (RangeSequence)x1_Source.Next;
            }
            var init = 0;
            while (x1_Source.HasValue)
            {
                init = AddInts(init, x1_Source.Value);
                x1_Source = (RangeSequence)x1_Source.Next;
                x1_Predicate = x1_Predicate;
                while (x1_Source.HasValue && !x1_Predicate(x1_Source.Value))
                {
                    x1_Source = (RangeSequence)x1_Source.Next;
                }
            }
            Assert.AreEqual(init, r);
        }

        // Expansion 7: Inlining more function calls.
        {
            var x1_Source = new RangeSequence(0, 1000);
            while ((x1_Source.Count > 0) && !Lt5(x1_Source.From))
            {
                x1_Source = new RangeSequence(x1_Source.From + 1, x1_Source.Count - 1); 
            }
            var init = 0;
            while ((x1_Source.Count > 0))
            {
                init = AddInts(init, x1_Source.From);
                x1_Source = new RangeSequence(x1_Source.From + 1, x1_Source.Count - 1);
                while ((x1_Source.Count > 0) && !Lt5(x1_Source.From))
                {
                    x1_Source = new RangeSequence(x1_Source.From + 1, x1_Source.Count - 1);
                }
            }
            Assert.AreEqual(init, r);
        }

        // Expansion 8: Expanding the RangeSequence to local variables 
        {
            var x1_Source_From = 0;
            var x1_Source_Count = 1000;
            while ((x1_Source_Count > 0) && !Lt5(x1_Source_From))
            {
                x1_Source_From = x1_Source_From + 1;
                x1_Source_Count = x1_Source_Count - 1;
            }
            var init = 0;
            while (x1_Source_Count > 0)
            {
                init = AddInts(init, x1_Source_From);
                x1_Source_From = x1_Source_From + 1;
                x1_Source_Count = x1_Source_Count - 1;
                while ((x1_Source_Count > 0) && !Lt5(x1_Source_From))
                {
                    x1_Source_From = x1_Source_From + 1;
                    x1_Source_Count = x1_Source_Count - 1;
                }
            }
            Assert.AreEqual(init, r);
        }

        // Expansion 9 (Lambda Expansion)
        {
            var x1_Source_From = 0;
            var x1_Source_Count = 1000;
            while ((x1_Source_Count > 0) && !(x1_Source_From < 5))
            {
                x1_Source_From = x1_Source_From + 1;
                x1_Source_Count = x1_Source_Count - 1;
            }
            var init = 0;
            while (x1_Source_Count > 0)
            {
                init = init + x1_Source_From;
                x1_Source_From = x1_Source_From + 1;
                x1_Source_Count = x1_Source_Count - 1;
                while ((x1_Source_Count > 0) && !(x1_Source_From < 5))
                {
                    x1_Source_From = x1_Source_From + 1;
                    x1_Source_Count = x1_Source_Count - 1;
                }
            }
            Assert.AreEqual(init, r);
        }

        // Expansion 10 (Assignment Simplification)
        {
            var x1_Source_From = 0;
            var x1_Source_Count = 1000;
            while ((x1_Source_Count > 0) && !(x1_Source_From < 5))
            {
                x1_Source_From += 1;
                x1_Source_Count -= 1;
            }
            var init = 0;
            while (x1_Source_Count > 0)
            {
                init += x1_Source_From;
                x1_Source_From += 1;
                x1_Source_Count -= 1;
                while ((x1_Source_Count > 0) && !(x1_Source_From < 5))
                {
                    x1_Source_From += 1;
                    x1_Source_Count -= 1;
                }
            }
            Assert.AreEqual(init, r);
        }
    }