JuliaLang/julia

Choose target ISA in `@code_llvm` and `@code_native`

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#52,949 opened on Jan 17, 2024

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featuregood first issue

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Description

@vchuravy mentioned on slack that it should be possible to teach @code_llvm and @code_native to generate code for a different ISA (but within same architecture) than the target chosen at startup with -C (native by default), with the only caveat that it'd work only for ISAs that are equal to or smaller than the current one.

A nice use case for this would be to able to choose the target in Compiler Explorer, whose julia backend at the moment only generates code for whatever is the native CPU currently being used.

It'd be nice to have pointers of where one would need to look at, in case they were interested in tackling the issue :slightly_smiling_face:

Contributor guide

Research direction
Investigate how `@code llvm` and `@code native` currently use the target machine. The goal is to allow specifying a different ISA (within same architecture) by overriding the target triple or CPU features. Look into the macro expansion in `base/compiler/` and how LLVM passes are set up. Key files: `base/compiler/optimize.jl`, `base/ircode.jl`, and possibly `base/compiler/llvmjit.jl`. Understand the existing command line option ` C` and how to pass similar options dynamically.
Tech stack
julia
Domain
compilers
Issue type
Feature
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.
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
Julia
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
65