FastExpressionCompiler

Targets .NET 6+, .NET 4.5+, .NET Standard 2.0+

NuGet packages:

• FastExpressionCompiler
  • sources package: FastExpressionCompiler.src
  • sources with the public code made internal: FastExpressionCompiler.Internal.src
• FastExpressionCompiler.LightExpression
  • sources package: FastExpressionCompiler.LightExpression.src
  • sources with the public code made internal: FastExpressionCompiler.LightExpression.Internal.src

The project was originally a part of the DryIoc, so check it out ;-)

The problem

ExpressionTree compilation is used by the wide variety of tools, e.g. IoC/DI containers, Serializers, ORMs and OOMs. But Expression.Compile() is just slow. Moreover the compiled delegate may be slower than the manually created delegate because of the reasons:

TL;DR;

Expression.Compile creates a DynamicMethod and associates it with an anonymous assembly to run it in a sand-boxed environment. This makes it safe for a dynamic method to be emitted and executed by partially trusted code but adds some run-time overhead.

See also a deep dive to Delegate internals.

The solution

The FastExpressionCompiler .CompileFast() extension method is 10-40x times faster than .Compile().
The compiled delegate may be in some cases a lot faster than the one produced by .Compile().

Note: The actual performance may vary depending on the multiple factors: platform, how complex is expression, does it have a closure, does it contain nested lambdas, etc.

In addition, the memory consumption taken by the compilation will be much smaller (check the Allocated column in the benchmarks below).

Benchmarks

Updated to .NET 8.0

BenchmarkDotNet v0.13.10, Windows 11 (10.0.22621.2428/22H2/2022Update/SunValley2)
11th Gen Intel Core i7-1185G7 3.00GHz, 1 CPU, 8 logical and 4 physical cores
.NET SDK 8.0.100-rc.2.23502.2
[Host]     : .NET 8.0.0 (8.0.23.47906), X64 RyuJIT AVX2
DefaultJob : .NET 8.0.0 (8.0.23.47906), X64 RyuJIT AVX2

Hoisted expression with the 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	Error	StdDev	Median	Ratio	RatioSD	Gen0	Gen1	Allocated	Alloc Ratio
Compile	121.969 us	2.4180 us	5.6040 us	120.830 us	35.77	2.46	0.7324	-	4.49 KB	2.92
CompileFast	3.406 us	0.0677 us	0.1820 us	3.349 us	1.00	0.00	0.2441	0.2365	1.54 KB	1.00

Invoking the compiled delegate (comparing to the direct constructor call):

Method	Mean	Error	StdDev	Median	Ratio	RatioSD	Gen0	Allocated	Alloc Ratio
DirectConstructorCall	5.734 ns	0.1501 ns	0.2745 ns	5.679 ns	0.86	0.05	0.0051	32 B	1.00
CompiledLambda	6.857 ns	0.1915 ns	0.5434 ns	6.704 ns	1.01	0.09	0.0051	32 B	1.00
FastCompiledLambda	6.746 ns	0.1627 ns	0.1442 ns	6.751 ns	1.00	0.00	0.0051	32 B	1.00

Hoisted expression with the 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	Error	StdDev	Ratio	RatioSD	Gen0	Gen1	Allocated	Alloc Ratio
Compile	442.02 us	8.768 us	21.998 us	40.00	2.34	1.9531	0.9766	12.04 KB	2.61
CompileFast	11.06 us	0.221 us	0.441 us	1.00	0.00	0.7324	0.7019	4.62 KB	1.00

Invoking compiled delegate comparing to direct method call:

Method	Mean	Error	StdDev	Ratio	RatioSD	Gen0	Allocated	Alloc Ratio
DirectMethodCall	35.51 ns	0.783 ns	1.308 ns	0.86	0.08	0.0267	168 B	1.62
Invoke_Compiled	1,096.15 ns	21.507 ns	41.437 ns	27.15	2.75	0.0420	264 B	2.54
Invoke_CompiledFast	37.65 ns	1.466 ns	4.299 ns	1.00	0.00	0.0166	104 B	1.00

Manually composed expression with parameters and closure

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

Compiling expression:

Method	Mean	Error	StdDev	Median	Ratio	RatioSD	Gen0	Gen1	Allocated	Alloc Ratio
Compile_SystemExpression	89.076 us	2.6699 us	7.6605 us	85.180 us	28.12	3.05	0.7324	0.4883	4.74 KB	3.41
CompileFast_SystemExpression	3.138 us	0.0550 us	0.0565 us	3.118 us	0.99	0.03	0.2213	0.2136	1.39 KB	1.00
CompileFast_LightExpression	3.180 us	0.0602 us	0.0591 us	3.163 us	1.00	0.00	0.2213	0.2136	1.39 KB	1.00

Invoking the compiled delegate compared to the normal delegate and the direct call:

Method	Mean	Error	StdDev	Median	Ratio	RatioSD	Gen0	Allocated	Alloc Ratio
DirectCall	8.388 ns	0.2655 ns	0.7575 ns	8.092 ns	1.00	0.07	0.0051	32 B	1.00
Compiled_SystemExpression	9.474 ns	0.1870 ns	0.4105 ns	9.381 ns	1.10	0.05	0.0051	32 B	1.00
CompiledFast_SystemExpression	8.575 ns	0.1624 ns	0.1440 ns	8.517 ns	1.00	0.02	0.0051	32 B	1.00
CompiledFast_LightExpression	8.584 ns	0.0776 ns	0.0862 ns	8.594 ns	1.00	0.00	0.0051	32 B	1.00

FastExpressionCompiler.LightExpression.Expression vs System.Linq.Expressions.Expression

FastExpressionCompiler.LightExpression.Expression is the lightweight version of System.Linq.Expressions.Expression. It is designed to be a drop-in replacement for the System Expression - just install the FastExpressionCompiler.LightExpression package instead of FastExpressionCompiler and replace the usings

using System.Linq.Expressions;
using static System.Linq.Expressions.Expression;

with

using static FastExpressionCompiler.LightExpression.Expression;
namespace FastExpressionCompiler.LightExpression.UnitTests

You may look at it as a bare-bone wrapper for the computation operation node which helps you to compose the computation tree (without messing with the IL emit directly). It won't validate operations compatibility for the tree the way System.Linq.Expression does it, and partially why it is so slow. Hopefully you are checking the expression arguments yourself and not waiting for the Expression exceptions to blow-up.

Sample expression

Creating the expression:

Method	Mean	Error	StdDev	Ratio	RatioSD	Gen0	Allocated	Alloc Ratio
Create_SystemExpression	1,039.5 ns	20.75 ns	45.98 ns	8.29	0.50	0.2060	1304 B	2.63
Create_LightExpression	125.7 ns	2.46 ns	5.99 ns	1.00	0.00	0.0789	496 B	1.00
Create_LightExpression_with_intrinsics	130.0 ns	2.47 ns	6.25 ns	1.04	0.07	0.0777	488 B	0.98

Creating and compiling:

Method	Mean	Error	StdDev	Ratio	RatioSD	Gen0	Gen1	Allocated	Alloc Ratio
Create_SystemExpression_and_Compile	159.184 us	2.9731 us	7.1235 us	37.34	1.65	0.9766	0.4883	7.4 KB	3.06
Create_SystemExpression_and_CompileFast	5.923 us	0.0996 us	0.1771 us	1.34	0.05	0.5188	0.5035	3.27 KB	1.35
Create_LightExpression_and_CompileFast	4.399 us	0.0484 us	0.0453 us	1.00	0.00	0.3815	0.3662	2.42 KB	1.00
CreateLightExpression_and_CompileFast_with_intrinsic	4.384 us	0.0835 us	0.0697 us	1.00	0.02	0.3815	0.3662	2.35 KB	0.97

Difference between FastExpressionCompiler and FastExpressionCompiler.LightExpression

FastExpressionCompiler

• Provides the CompileFast extension methods for the System.Linq.Expressions.LambdaExpression.

FastExpressionCompiler.LightExpression

• Provides the CompileFast extension methods for FastExpressionCompiler.LightExpression.LambdaExpression.
• Provides the drop-in expression replacement with the less consumed memory and the faster construction at the cost of the less validation.
• Includes its own ExpressionVisitor.
• Supports ToExpression method to convert back to the System.Linq.Expressions.Expression.

Both FastExpressionCompiler and FastExpressionCompiler.LightExpression

• Support ToCSharpString() method to output the compile-able C# code represented by expression.
• Support ToExpressionString() method to output the expression construction C# code, so given the expression object you'll get e.g. Expression.Lambda(Expression.New(...)).

Who's using it

Marten, Rebus, StructureMap, Lamar, ExpressionToCodeLib, NServiceBus, LINQ2DB, MapsterMapper

Considering: Moq, Apex.Serialization

How to use

Install from the NuGet and add the using FastExpressionCompiler; and replace the call to the .Compile() with the .CompileFast() extension method.

Note: CompileFast has an optional parameter bool ifFastFailedReturnNull = false to disable fallback to Compile.

Examples

Hoisted lambda expression (created by the C# 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(_ctorX,
        Expression.Constant(a, typeof(A)), bParamExpr),
    bParamExpr);

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

Note: You may simplify Expression usage and enable faster refactoring with the C# using static statement:

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

var a = new A();
var bParamExpr = Parameter(typeof(B), "b");
var expr = Lambda(
    New(_ctorX, Constant(a, typeof(A)), bParamExpr),
    bParamExpr);

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

How it works

The idea is to provide the fast compilation for the supported expression types and fallback to the system Expression.Compile() for the not supported types:

What's not supported yet

FEC does not support yet:

• Quote
• Dynamic
• RuntimeVariables
• DebugInfo
• MemberInit with the MemberMemberBinding and the ListMemberBinding binding types
• NewArrayInit multi-dimensional array initializer is not supported yet

To find what nodes are not supported in your expression you may use the technic described below in the Diagnostics section.

The compilation is done by traversing the expression nodes and emitting the IL. The code is tuned for the performance and the minimal memory consumption.

The expression is traversed twice:

• 1st round is to collect the constants and nested lambdas into the closure objects.
• 2nd round is to emit the IL code and create the delegate using the DynamicMethod.

If visitor finds the not supported expression node or the error condition, the compilation is aborted, and null is returned enabling the fallback to System .Compile().

Diagnostics and Code Generation

FEC V3 has added powerful diagnostics and code generation tools.

Diagnostics

You may pass the optional CompilerFlags.EnableDelegateDebugInfo into the CompileFast methods.

EnableDelegateDebugInfo adds the diagnostic info into the compiled delegate including its source Expression and C# code. Can be used as following:

var f = e.CompileFast(true, CompilerFlags.EnableDelegateDebugInfo);
var di = f.Target as IDelegateDebugInfo;
Assert.IsNotNull(di.Expression);
Assert.IsNotNull(di.ExpressionString);
Assert.IsNotNull(di.CSharpString);

ThrowOnNotSupportedExpression and NotSupported_ flags

FEC V3.1 has added the compiler flag CompilerFlags.ThrowOnNotSupportedExpression. When passed to CompileFast(flags: CompilerFlags.ThrowOnNotSupportedExpression) and the expression contains not (yet) supported Expression node the compilation will throw the exception instead of returning null.

To get the whole list of the not yet supported cases you may check in Result.NotSupported_ enum values.

Code Generation

The Code Generation capabilities are available via the ToCSharpString and ToExpressionString extension methods.

Note: When converting the source expression to either C# code or to the Expression construction code you may find the // NOT_SUPPORTED_EXPRESSION comments marking the not supported yet expressions by FEC. So you may test the presence or absence of this comment.

Additional optimizations

1. Using FastExpressionCompiler.LightExpression.Expression instead of System.Linq.Expressions.Expression for the faster expression creation.
2. Using .TryCompileWithPreCreatedClosure and .TryCompileWithoutClosure methods when you know the expression at hand and may skip the first traversing round, e.g. for the "static" expression which does not contain the bound constants. Note: You cannot skip the 1st round if the expression contains the Block, Try, or Goto expressions.

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