dotnet/runtime

JIT: missing opportunities in constant folding around bitwise ops

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#95,747 opened on Dec 7, 2023

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Description

int Test(int x, int y) => (x | 5) | (y | 3); // E.g. Enums

Current asm:

; Method Program:Test(int,int):int:this (FullOpts)
       or       edx, 5
       mov      eax, edx
       or       eax, r8d
       or       eax, 3
       ret      
; Total bytes of code: 12

Expected asm:

       mov      eax, edx
       or       eax, r8d
       or       eax, 7
       ret      
; Total bytes of code: 9

Contributor guide

Research direction
Investigate the constant folding optimization in the JIT's lowering phase for bitwise OR operations. Identify why the JIT does not combine constants into a single constant and propose a fix.
Tech stack
csharp
Domain
compilers
Issue type
Performance
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
4
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
3-5 days
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
C#Git
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
40