rustc_codegen_gcc: Progress Report #11

What is rustc_codegen_gcc?

rustc_codegen_gcc is a GCC codegen for rustc, meaning that it can be loaded by the existing rustc frontend, but benefits from GCC by having more architectures supported and having access to GCC’s optimizations.

GCC patches status

There was a lot of progress this month! The following patches were reviewed and merged upstream:

This means that they will be included in the GCC 12 release which should happen in the following days! This also means that all of my patches that were sent for review were merged. I still have a few that I need to prepare and send for review and I’ll send them on the GCC mailing list this month.

State of rustc_codegen_gcc

Since GCC 12 will be released soon, I started looking at rustup in order to allow distributing the GCC codegen along with libgccjit via rustup. Unfortunately, there’s a step before creating the distribution artifacts that panics, so we’re not there yet, but I will continue looking into this when this issue is fixed.

Here’s what has been done this month:

The work on SIMD is still not completed as I cannot compile stdarch yet, but there’s been good progress. Some of the complexity comes from the fact that there’s not a one-to-one mapping for some SIMD intrinsics.

Here’s a rough summary of what has been implemented:

Feature Completion

target-specific builtins support in libgccjit


support for vector shuffle (equivalent of __builtin_shufflevector) in libgccjit




simd_select, simd_select_bitmask


simd_reduce_min, simd_reduce_max


simd_reduce_and, simd_reduce_or


simd_saturating_add and simd_saturating_sub

implemented for x86

LLVM SIMD intrinsics

~70% implemented for x86

simd_reduce_add_unordered, simd_reduce_mul_unordered

50% implemented


20% implemented


20% implemented

simd_reduce_add_ordered, simd_reduce_mul_ordered


simd_reduce_min_nanless, simd_reduce_max_nanless


simd_reduce_xor, simd_reduce_all, simd_reduce_any


SIMD float intrinsics




simd_gather and simd_scatter




UI tests progress

Here are the results of running the UI tests in the CI:

Category Last Month This Month Delta









For the next month, I’ll continue working on SIMD support.

How to contribute


If you want to help on the project itself, please do the following:

  1. Run the tests locally.

  2. Choose a test that fails.

  3. Investigate why it fails.

  4. Fix the problem.

Even if you can’t fix the problem, your investigation could help, so if you enjoy staring at assembly code, have fun!

Crates and rustc

If you would like to contribute on adding support for Rust on currently unsupported platforms, you can help by adding the support for those platforms in some crates like libc and object and also in the rust compiler itself.

Test this project

Otherwise, you can test this project on new platforms and also compare the assembly with LLVM to see if some optimization is missing.

Good first issue

Finally, another good way to help is to look at good first issues. Those are issues that should be easier to start with.

Thanks for your support!

I wanted to personally thank all the people that sponsor this project: your support is very much appreciated.

A special thanks to the following sponsors:

  • saethlin

  • embark-studios

  • Traverse-Research

  • Shnatsel

A big thank you to bjorn3 for his help, contributions and reviews. And a big thank you to lqd and GuillaumeGomez for answering my questions about rustc’s internals. Another big thank you to Commeownist for his contributions.

Also, a big thank you to the rest of my sponsors:

  • kpp

  • 0x7CFE

  • repi

  • nevi-me

  • oleid

  • acshi

  • joshtriplett

  • djc

  • TimNN

  • sdroege

  • pcn

  • alanfalloon

  • steven-joruk

  • davidlattimore

  • Nehliin

  • colelawrence

  • zmanian

  • alexkirsz

  • regiontog

  • berkus

  • belzael

  • vincentdephily

  • jam1garner

  • yvt

  • Shoeboxam

  • evanrichter

  • yerke

  • bes

  • seanpianka

  • srijs

  • kkysen

  • messense

  • riking

  • rafaelcaricio

  • Lemmih

  • memoryruins

  • pthariensflame

  • senden9

  • robjtede

  • Jonas Platte

  • zebp

  • spike grobstein

  • Oliver Marshall

  • Sam Harrington

  • Jonas

  • Jeff Muizelaar

  • Chris Butler

  • sierrafiveseven

  • Joseph Garvin

  • MarcoFalke

  • icewind

  • Tommy Thorn

  • Sebastian Zivota

  • Oskar Nehlin

  • Nicolas Barbier

  • Daniel

  • Thomas Colliers

  • Justin Ossevoort

  • sbstp

  • Chris

  • Bálint Horváth

  • fanquake

  • sstadick

  • luizirber

  • kiyoshigawa

  • robinmoussu

  • Daniel Sheehan

  • Marvin Löbel

  • nacaclanga

and a few others who preferred to stay anonymous.

Former sponsors/patreons:

  • igrr

  • finfet

  • Alovchin91

  • wezm

  • stuhood

  • mexus

  • raymanfx

  • 0xdeafbeef

  • ghost

  • gilescope

  • Hofer-Julian

  • olanod

  • Denis Zaletaev

  • Chai T. Rex

  • Paul Ellenbogen

  • Dakota Brink

  • Botlabs

  • Cass

  • Oliver Marshall