dotnet/roslyn

Find and pass "op_Equality" MethodInfo to the expression tree factory for Equals.

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#11,336 opened on May 16, 2016

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Area-CompilersBugLanguage-C#Language-VBTenet-Performancehelp wanted

Description

Not passing the method only results in forcing the "Equals" to search for the method using reflection when it is called. We would get the same expression tree, but will do more allocations.

"op_Equality" is a Special method and a part of public API of System.String Obtaining "op_Equality" at compile time is cheap and already done in all cases except when Expression Trees are involved. Note: We can rely on the operator always be there (it is likely an error if it is not in the first place), and if not, we can still pass "null", although that would be a nearly impossible case in reality which would likely fail at run time before producing any trees anyways.

The situation is worse on CoreFX because of additional allocation due to the use of more general (and more expensive) reflection APIs (see: https://github.com/dotnet/corefx/issues/8576 )

The issue was reported as causing excessive and unnecessary allocations in common patterns used by ASP.Net apps. A typical example is https://github.com/aspnet/MusicStore.

Contributor guide

Tech stack
csharp
Domain
performancebackend
Issue type
performance
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
C# basicsExpression treesReflection APIMethodInfo
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
40
Research direction
The issue is to modify the expression tree factory to pass the MethodInfo for op Equality when building Equals expressions. Look for existing usage of MethodInfo in expression tree generation in the Roslyn compiler source code, particularly in files related to expression compilation. Ensure that reflection is avoided and allocations reduced. Reference the linked corefx issue for additional context.