rustc_codegen_gcc: Progress Report #14

What is rustc_codegen_gcc?

rustc_codegen_gcc is a GCC ahead-of-time 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. It is not to be confused with gccrs, which is a GCC frontend for Rust.

LPC 2022

I’ll be presenting at the Linux Plumbers Conference in Dublin next month. Make sure to attend if you want to discuss using this codegen for any specific purposes.

GCC patches status

This month, I did the following:

Those commits are not yet posted as patches for review since there are not ready.

State of rustc_codegen_gcc

Here’s what has been done this month:

I also looked at CPU features detection, but I haven’t anything working for now.

Here is the progress of the stdarch tests:

test result: FAILED. 4553 passed; 23 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.89s
Category Last Month This Month Delta

Passed

4548

4553

+5

Failed

28

23

-5

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

Feature Last month completion Completion Delta

target-specific builtins support in libgccjit

Done

support for vector shuffle (equivalent of __builtin_shufflevector) in libgccjit

Done

simd_extract

Done

simd_select, simd_select_bitmask

Done

simd_reduce_min, simd_reduce_max

Done

simd_reduce_and, simd_reduce_or

Done

simd_saturating_add and simd_saturating_sub

implemented for x86

simd_insert

Done

simd_cast

Done

simd_bitmask

Done

LLVM SIMD intrinsics

~99% implemented for x86

~99% implemented for x86

0 (needs to fix some bugs)

simd_reduce_add_unordered, simd_reduce_mul_unordered

50%

50%

0

simd_reduce_add_ordered, simd_reduce_mul_ordered

0%

0%

0

simd_reduce_min_nanless, simd_reduce_max_nanless

0%

0%

0

simd_reduce_xor, simd_reduce_all, simd_reduce_any

0%

0%

0

SIMD float intrinsics

0%

0%

0

simd_gather and simd_scatter

0%

0%

0

simd_as

0%

0%

0

UI tests progress

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

Category Last Month This Month Delta

Passed

4698

4698

0

Failed

57

57

0

For the next month, I’ll continue working on SIMD support: debugging those tests and fixing the issues found.

Summary of the failing UI tests.

There was no progress on those tests this month, but I wanted to show a summary describing those failing tests:

Category Number of failing tests

Target features

1

Panic

1

Undefined reference

2

Simd

19

Allocator

9

Asm

3

Unwinding

3

Async

3

Emit IR

1

LTO

10

Debug info

2

NaN (float)

2

Segfault

1 (this one is on rust’s side)

Those do not include some of the tests that were intentionally disabled for now since the feature is not supported yet (LTO and unwinding, mainly).

How to contribute

rustc_codegen_gcc

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

  • Eugene Bulkin

  • Absolucy

  • Chris Butler

  • sierrafiveseven

  • Joseph Garvin

  • MarcoFalke

  • athre0z

  • 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

  • Matthew Conolly

  • dandxy89

  • 0x0177b11f

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