FastExpressionCompiler

Supported platforms: .NET 4.5+, .NET Standard 1.3, .NET Standard 2.0

Why

Expression tree compilation is used by wide range of tools, e.g. IoC/DI containers, Serializers, OO Mappers. But the performance of compilation with Expression.Compile() is just slow. Moreover, the compiled delegate may be slower than manually created delegate because of the reasons:

TL;DR;

The question is, why is the compiled delegate way slower than a manually-written delegate? Expression.Compile creates a DynamicMethod and associates it with an anonymous assembly to run it in a sandboxed environment. This makes it safe for a dynamic method to be emitted and executed by partially trusted code but adds some run-time overhead.

Fast Expression Compiler is ~20 times faster than Expression.Compile().
The compiled delegate may be in some cases??? ~15 times faster than the one produced by Expression.Compile().

Benchmarks

BenchmarkDotNet=v0.10.3.0, OS=Microsoft Windows 10.0.14393
Processor=Intel(R) Core(TM) i5-6300U CPU 2.40GHz, ProcessorCount=4
Frequency=2437493 Hz, Resolution=410.2576 ns, Timer=TSC
dotnet cli version=1.0.0-preview2-1-003177
  [Host]     : .NET Core 4.6.24628.01, 64bit RyuJIT
  DefaultJob : .NET Core 4.6.24628.01, 64bit RyuJIT

Hoisted expression with constructor and two arguments in closure

    var a = new A();
    var b = new B();
    Expression<Func<X>> e = () => new X(a, b);

Compiling expression:

Method	Mean	StdDev	Scaled	Scaled-StdDev	Gen 0	Gen 1	Allocated
ExpressionCompile	426.1452 us	10.8108 us	29.91	1.15	-	-	4.36 kB
ExpressionCompileFast	14.2593 us	0.4461 us	1.00	0.00	1.0579	0.2035	2.72 kB

Invoking compiled delegate comparing to direct constructor call:

Method	Mean	StdErr	StdDev	Scaled	Scaled-StdDev	Gen 0	Allocated
DirectConstructorCall	9.7089 ns	0.1423 ns	0.5692 ns	0.70	0.04	0.0202	32 B
CompiledLambda	15.8753 ns	0.2077 ns	1.2113 ns	1.15	0.09	0.0198	32 B
FastCompiledLambda	13.8102 ns	0.0963 ns	0.3473 ns	1.00	0.00	0.0195	32 B

Hoisted expression with static method and two nested lambdas and two arguments in closure

    var a = new A();
    var b = new B();
    Expression<Func<X>> getXExpr = () => CreateX((aa, bb) => new X(aa, bb), new Lazy<A>(() => a), b);

Compiling expression:

Method	Mean	StdDev	Scaled	Scaled-StdDev	Gen 0	Gen 1	Allocated
ExpressionCompile	885.8788 us	14.5933 us	17.07	0.37	-	-	12.28 kB
ExpressionFastCompile	51.9052 us	0.7952 us	1.00	0.00	4.0616	1.3761	8 kB

Invoking compiled delegate comparing to direct method call:

Method	Mean	StdDev	Scaled	Scaled-StdDev	Gen 0	Allocated
DirectMethodCall	166.9818 ns	3.0175 ns	0.86	0.02	0.1111	184 B
CompiledLambda	2,547.4770 ns	46.7880 ns	13.08	0.27	0.0900	280 B
FastCompiledLambda	194.8093 ns	2.2769 ns	1.00	0.00	0.1399	240 B

Manually composed expression with parameters and closure

    var a = new A();
    var bParamExpr = Expression.Parameter(typeof(B), "b");

    var expr = Expression.Lambda(
        Expression.New(typeof(X).GetTypeInfo().DeclaredConstructors.First(),
            Expression.Constant(a, typeof(A)), bParamExpr),
        bParamExpr);

Compiling expression:

Method	Mean	StdDev	Median	Scaled	Scaled-StdDev	Gen 0	Gen 1	Allocated
CompileExpression	397.5570 us	27.6319 us	386.6312 us	27.46	1.92	-	-	4.72 kB
CompileFastExpression	14.4785 us	0.1752 us	14.5392 us	1.00	0.00	1.3086	0.5762	2.26 kB

Invoking compiled delegate comparing to normal delegate:

Method	Mean	StdErr	StdDev	Scaled	Scaled-StdDev	Gen 0	Allocated
RawLambda	12.5377 ns	0.0839 ns	0.3249 ns	0.93	0.03	0.0196	32 B
CompiledLambda	14.2297 ns	0.1640 ns	0.6135 ns	1.06	0.05	0.0195	32 B
FastCompiledLambda	13.4183 ns	0.0352 ns	0.1317 ns	1.00	0.00	0.0195	32 B

Manually composed complex ExpressionInfo

FastExpressionCompiler.ExpressionInfo is the lightweight version of Expression. You may consider it instead of Expression when you are validating the Expression arguments on your own, and not relying on Expression composition exceptions.

Note: Explore ExpressionInfo class in FastExpressionCompiler.cs for finding the supported expression types.

Method	Mean	StdDev	Scaled	Scaled-StdDev	Gen 0	Gen 1	Allocated
CreateExpression_and_Compile	632.4135 us	26.5744 us	32.37	1.72	-	-	7.81 kB
CreateExpression_and_CompileFast	29.7829 us	1.6242 us	1.52	0.10	1.8694	0.6487	3.86 kB
CreateExpressionInfo_and_CompileFast	19.5569 us	0.6645 us	1.00	0.00	1.4689	0.3703	3.38 kB

Usage

Hoisted lambda expression (created by compiler):

    var a = new A(); var b = new B();
    Expression<Func<X>> expr = () => new X(a, b);

    var getX = expr.CompileFast();
    var x = getX();

Manually composed lambda expression:

    var a = new A();
    var bParamExpr = Expression.Parameter(typeof(B), "b");
    var expr = Expression.Lambda(
        Expression.New(typeof(X).GetTypeInfo().DeclaredConstructors.First(),
            Expression.Constant(a, typeof(A)), bParamExpr),
        bParamExpr);

    var getX = expr.CompileFast();
    var x = getX(new B());

Status

Initially developed and currently used in DryIoc.

Used in Marten v2, ExpressionToCodeLib.

What is supported:

Manually created or hoisted lambda expressions with closure
Nested lambdas
Constructor and method calls, lambda invocation
Property and member access
Equality and ?: operators

What is not supported:

??, ?., bitwise, and ariphmetic operators
Expression.Block and declarative expressions added in .NET 4.0
Check an open issues for more details

Note: The current limitations may be lifted by wrapping not yet supported expression into method or property.

How

The idea is to provide fast compilation of selected/supported expression types, and fall back to normal Expression.Compile() for the not (yet) supported types.

Compilation is done by visiting expression nodes and emitting the IL. The supporting code preserved as minimalistic as possible for perf.

Expression is visited in two rounds:

To collect constants and nested lambdas into closure objects.
To emit an IL.

If some processing round visits a not supported expression node, then compilation is aborted, and null is returned enabling the fallback to normal Expression.Compile().

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