SeregaZH / FastExpressionCompiler

Fast ExpressionTree compiler to delegate

FastExpressionCompiler

• Windows:
• Linux, MacOS:

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

Why

Expression tree compilation is used by wide range of tools, e.g. IoC/DI containers, Serializers, OO Mappers. But 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 up to ~20 times faster than Expression.Compile().
The compiled delegate may be in some cases up to ~15 times faster than one produced by Expression.Compile().

Note: The actual performance in your case will depend on multiple factors: how complex is expression, does it have a closure over the values, does it have a nested lambdas, etc.

How to install

Either from NuGet or grab a single FastExpressionCompiler.cs file.

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

ExpressionInfo vs Expression

FastExpressionCompiler.ExpressionInfo is the lightweight version of Expression. You may look at it as just a thin wrapper on operation node which helps you to compose the computation tree. But it won't do any node compatibility verification for the tree as the Expression does (and why it is slow). Hopefully, you are checking the expression arguments yourself, and not waiting for Expression exceptions to blow up.

Note: At the moment ExpressionInfo is not supported for all supported expression types (#46).

Creating expression:

Method	Mean	Error	StdDev	Median	Scaled	ScaledSD	Gen 0	Allocated
CreateExpression	6.788 us	0.2688 us	0.7625 us	6.537 us	4.00	0.50	0.9003	1424 B
CreateExpressionInfo	1.703 us	0.0364 us	0.0973 us	1.691 us	1.00	0.00	0.5951	936 B

Creating and compiling:

Method	Mean	Error	StdDev	Median	Scaled	ScaledSD	Gen 0	Gen 1	Gen 2	Allocated
CreateExpression_and_Compile	648.73 us	12.7079 us	18.2253 us	644.46 us	35.28	1.94	3.9063	1.9531	-	7.32 KB
CreateExpression_and_CompileFast	30.30 us	1.3381 us	3.7301 us	28.89 us	1.65	0.22	2.3804	1.1597	-	3.69 KB
CreateExpressionInfo_and_CompileFast	18.43 us	0.3662 us	0.9321 us	18.12 us	1.00	0.00	2.0447	1.0071	0.0305	3.15 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());

Lambda ExpressionInfo:

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

        bParamExpr);

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

Note: The way to simplify your life when working with expressions is C# 6 using static construct

    using static System.Linq.Expressions.Expression;
// or
//  using static FastExpressionCompiler.ExpressionInfo;

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

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

State

Originally the project is part of DryIoc, then split for more general adoption.

Some users: Marten, Rebus, 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
• Expression.Assign, Block and TryCatch
• Ariphmetic operators

Complete list of supported expression types may be found in this switch

Note: If the currently not supported expressions may be wrapped in a method or property, then it will make them supported.

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:

1. To collect constants and nested lambdas into closure objects.
2. 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().