Stabilize 29 RISC-V target features (`riscv_ratified_v2`) #145948

a4lg · 2025-08-28T00:06:17Z

This commit stabilizes RISC-V target features with following constraints:

Describes a ratified extension.
Implemented on Rust 1.88.0 or before.
Waiting for four+ version cycles seems sufficient.
Does not disrupt current rustc's target feature (cf. Need comprehensive story for target_feature compat #140570) + ABI (cf. Some -Ctarget-features must be restrained on RISCV #132618) handling.
It excludes E and all floating point-arithmetic extensions. The Zfinx family does not involve floating point registers but not stabilizing for now to avoid possible confusion between the F extension family.
Not vector-related (floating point and integer).
While integer vector subsets should not cause any ABI issues (as they don't use ABI-dependent floating point registers), we need to discuss before stabilizing them.
Supported by the lowest LLVM version supported by rustc (LLVM 20).

List of target features to be stabilized:

b
za64rs (no-RT)
za128rs (no-RT)
zaamo
zabha
zacas
zalrsc
zama16b (no-RT)
zawrs
zca
zcb
zcmop
zic64b (no-RT)
zicbom
zicbop (no-RT)
zicboz
ziccamoa (no-RT)
ziccif (no-RT)
zicclsm (no-RT)
ziccrse (no-RT)
zicntr
zicond
zicsr
zifencei
zihintntl
zihintpause
zihpm
zimop
ztso

Of which, 20 of them (29 minus 9 "no-RT" target features) support runtime detection through std::arch::is_riscv_feature_detected!().

Corresponding PR for the Reference: rust-lang/reference#1987

Description in older revision(s)

Not vector-related (including not FP-related ones).
No ABI issues will not occur unless floating point registers are involved. But for integer-only vector ones, we'll be stabilizing in another time.

The original text is rewritten to avoid confusion as per @RalfJung's request.

Of which, 19 of them support runtime detection through std_detect.

This is rewritten to correlate this PR with a public API (instead of an internal crate).

r? @Amanieu
@rustbot label +O-riscv

rustbot · 2025-08-28T00:06:23Z

Some changes occurred in compiler/rustc_codegen_ssa

cc @WaffleLapkin

a4lg · 2025-08-28T00:18:32Z

I expect that this PR lands on the version 1.92 cycle (I chose extensions with relatively low risk factors) but happy if it could be merged in the version 1.91 cycle.

Amanieu · 2025-08-29T20:34:11Z

LGTM, these are all officially ratified RISC-V extensions.

@rfcbot merge

rust-rfcbot · 2025-08-29T20:34:13Z

traviscross · 2025-08-29T21:12:02Z

We'll need a PR to the Reference submitted and accepted ahead of this being merged.

@rfcbot reviewed

cc @rust-lang/lang-docs @RalfJung

a4lg · 2025-08-30T01:03:12Z

Consideration: Feature Naming (for `std_detect`)

The only initial intent of riscv_ratified_v2 (which feels a bit blunt) was to avoid crashing with existing riscv_ratified¹ and later noticed that x86 uses various feature names on stabilization.

I considered the similar after the initial submission but didn't for several reasons:

Many extensions to be stabilized are general purpose (even some of them are split from an early version of the I base ISA) and clear distinction will confuse the users between plain riscv_ratified (it's just a collection of extensions where runtime detection of them is stabilized in Rust 1.78.0 and contains rich extensions like scalar cryptography).
Considering future extensions to be stabilized in Rust and the history (some RISC-V extensions are split from others and semantic naming may not work in the near future), either of them seems inevitable:
1. Using the extension name itself or similar or
2. Using blunt version schemes like in this PR.

After consideration, I prefer blunt naming scheme (pure versioning regardless of the category) for runtime detection of RISC-V extensions.

Consideration: Deferring to Version 1.92 Cycle may Have its Benefit

Although I'll rush for the version 1.91 cycle if possible, I have to say that deferring this might be an option.

I'm talking about #145071, which raises the minimum LLVM version to 20. After this PR is merged, I think we can safely introduce the Zacas extension without riscv_ratified_v3 (I excluded Zacas from this PR because of this minimum LLVM version issue).

So, if we don't make it to the version 1.91 cycle, waiting for #145071 might be an option.

The same feature name does not allow multiple stabilized versions. ↩

The `Zb` extension does not exist and we instead have the `B` extension which is a superset of the three subextensions: `Zba`, `Zbb` and `Zbs`. This commit fixes this issue and updates the reference URL to the source code of the latest ratified ISA Manual (version 20250508). To align with rust-lang/rust#145948, this commit performs rename, not removal.

Because unstable "B" (incorrectly named as `zb`) was there, this commit adds 28 minus one ("B") new extensions to be stabilized. This commit directly corresponds to rust-lang/rust#145948. References: 1. RISC-V Instruction Set Manual (version 20250508): <https://github.com/riscv/riscv-isa-manual/tree/20250508> 2. RISC-V Profiles (version 1.0 - RVA23 is not stabilized at the time): <https://github.com/riscv/riscv-profiles/tree/v1.0> 3. RISC-V Profiles (RVA23/RVB23-ratified version): <https://github.com/riscv/riscv-profiles/tree/rva23-rvb23-ratified>

The `Zb` extension does not exist and we instead have the `B` extension which is a superset of the three subextensions: `Zba`, `Zbb` and `Zbs`. This commit fixes this issue and updates the reference URL to the source code of the latest ratified ISA Manual (version 20250508). To align with rust-lang/rust#145948, this commit performs rename, not removal.

Because unstable "B" (incorrectly named as `zb`) was there, this commit adds 28 minus one ("B") new extensions to be stabilized. This commit directly corresponds to rust-lang/rust#145948. References: 1. RISC-V Instruction Set Manual (version 20250508): <https://github.com/riscv/riscv-isa-manual/tree/20250508> 2. RISC-V Profiles (version 1.0 - RVA23 is not stabilized at the time): <https://github.com/riscv/riscv-profiles/tree/v1.0> 3. RISC-V Profiles (RVA23/RVB23-ratified version): <https://github.com/riscv/riscv-profiles/tree/rva23-rvb23-ratified>

The `Zb` extension does not exist and we instead have the `B` extension which is a superset of the three subextensions: `Zba`, `Zbb` and `Zbs`. This commit fixes this issue and updates the reference URL to the source code of the latest ratified ISA Manual (version 20250508). To align with rust-lang/rust#145948, this commit performs rename, not removal.

Because unstable "B" (incorrectly named as `zb`) was there, this commit adds 28 minus one ("B") new extensions to be stabilized. This commit directly corresponds to rust-lang/rust#145948. References: 1. RISC-V Instruction Set Manual (version 20250508): <https://github.com/riscv/riscv-isa-manual/tree/20250508> 2. RISC-V Profiles (version 1.0 - RVA23 is not stabilized at the time): <https://github.com/riscv/riscv-profiles/tree/v1.0> 3. RISC-V Profiles (RVA23/RVB23-ratified version): <https://github.com/riscv/riscv-profiles/tree/rva23-rvb23-ratified>

pthariensflame · 2025-12-11T02:45:14Z

So…the idea was to wait for the 1.92 cycle. But now we're on the 1.94 cycle. Any plans?

RalfJung · 2025-12-11T17:38:46Z

This is currently waiting for a checkbox by @BurntSushi, @scottmcm, or @the8472.

RalfJung · 2025-12-11T17:40:16Z

Also Cc @kito-cheng @michaelmaitland @robin-randhawa-sifive @topperc as Risc-V target maintainers, to double-check that these target features are safe to stabilize, in particular from an ABI perspective. :)

topperc · 2025-12-12T17:26:44Z

Also Cc @kito-cheng @michaelmaitland @robin-randhawa-sifive @topperc as Risc-V target maintainers, to double-check that these target features are safe to stabilize, in particular from an ABI perspective. :)

The list looks good to me.

rust-rfcbot · 2025-12-17T16:46:11Z

🔔 This is now entering its final comment period, as per the review above. 🔔

rust-rfcbot · 2025-12-27T16:48:43Z

The final comment period, with a disposition to merge, as per the review above, is now complete.

As the automated representative of the governance process, I would like to thank the author for their work and everyone else who contributed.

Amanieu · 2026-01-03T07:14:38Z

@bors r+

bors · 2026-01-03T07:14:41Z

📌 Commit 316a79f has been approved by Amanieu

It is now in the queue for this repository.

bors · 2026-01-03T07:26:39Z

⌛ Testing commit 316a79f with merge 00f49d2...

bors · 2026-01-03T10:43:21Z

☀️ Test successful - checks-actions
Approved by: Amanieu
Pushing 00f49d2 to main...

github-actions · 2026-01-03T10:46:16Z

What is this?

This is an experimental post-merge analysis report that shows differences in test outcomes between the merged PR and its parent PR.

Comparing 50d5940 (parent) -> 00f49d2 (this PR)

Test differences

Show 2 test diffs

2 doctest diffs were found. These are ignored, as they are noisy.

Test dashboard

Run

cargo run --manifest-path src/ci/citool/Cargo.toml -- \
    test-dashboard 00f49d22042dce59561b36eb075bbf5e343c23c4 --output-dir test-dashboard

And then open test-dashboard/index.html in your browser to see an overview of all executed tests.

Job duration changes

dist-apple-various: 3339.0s -> 4285.0s (+28.3%)
aarch64-gnu-llvm-20-1: 3558.7s -> 4070.3s (+14.4%)
dist-aarch64-msvc: 5569.5s -> 6358.1s (+14.2%)
dist-aarch64-llvm-mingw: 5821.1s -> 6594.4s (+13.3%)
dist-x86_64-illumos: 5804.8s -> 6331.2s (+9.1%)
x86_64-msvc-ext1: 7163.4s -> 7719.8s (+7.8%)
test-various: 7468.3s -> 6930.1s (-7.2%)
i686-gnu-nopt-2: 8091.8s -> 7509.1s (-7.2%)
dist-aarch64-linux: 6716.8s -> 6251.9s (-6.9%)
x86_64-gnu-llvm-21-1: 4476.1s -> 4173.4s (-6.8%)

How to interpret the job duration changes?

Job durations can vary a lot, based on the actual runner instance
that executed the job, system noise, invalidated caches, etc. The table above is provided
mostly for t-infra members, for simpler debugging of potential CI slow-downs.

rust-timer · 2026-01-03T11:24:00Z

Finished benchmarking commit (00f49d2): comparison URL.

Overall result: no relevant changes - no action needed

@rustbot label: -perf-regression

Instruction count

This benchmark run did not return any relevant results for this metric.

Max RSS (memory usage)

Results (secondary 3.2%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	3.2%	[3.2%, 3.2%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Cycles

This benchmark run did not return any relevant results for this metric.

Binary size

This benchmark run did not return any relevant results for this metric.

Bootstrap: 470.889s -> 472.503s (0.34%)
Artifact size: 390.82 MiB -> 390.81 MiB (-0.00%)

rustbot assigned Amanieu Aug 28, 2025

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. T-libs Relevant to the library team, which will review and decide on the PR/issue. labels Aug 28, 2025

rustbot added the O-riscv Target: RISC-V architecture label Aug 28, 2025

rust-rfcbot added proposed-final-comment-period Proposed to merge/close by relevant subteam, see T-<team> label. Will enter FCP once signed off. disposition-merge This issue / PR is in PFCP or FCP with a disposition to merge it. labels Aug 29, 2025

a4lg mentioned this pull request Aug 30, 2025

RISC-V Extensions update including 29 extensions to stabilize rust-lang/reference#1987

Merged

traviscross removed I-lang-nominated Nominated for discussion during a lang team meeting. P-lang-drag-1 Lang team prioritization drag level 1. https://rust-lang.zulipchat.com/#narrow/channel/410516-t-lang labels Oct 22, 2025

traviscross added the I-lang-nominated Nominated for discussion during a lang team meeting. label Dec 12, 2025

traviscross added the P-lang-drag-1 Lang team prioritization drag level 1. https://rust-lang.zulipchat.com/#narrow/channel/410516-t-lang label Dec 17, 2025

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rust-rfcbot removed the proposed-final-comment-period Proposed to merge/close by relevant subteam, see T-<team> label. Will enter FCP once signed off. label Dec 17, 2025

traviscross removed I-lang-nominated Nominated for discussion during a lang team meeting. P-lang-drag-1 Lang team prioritization drag level 1. https://rust-lang.zulipchat.com/#narrow/channel/410516-t-lang labels Dec 18, 2025

rustbot mentioned this pull request Dec 27, 2025

Tracking issue for release notes of #145948: Stabilize 29 RISC-V target features (riscv_ratified_v2) #150439

Open

bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Jan 3, 2026

bors added the merged-by-bors This PR was explicitly merged by bors. label Jan 3, 2026

bors merged commit 00f49d2 into rust-lang:main Jan 3, 2026
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rustbot added this to the 1.94.0 milestone Jan 3, 2026

bors mentioned this pull request Jan 3, 2026

std_detect: RISC-V: Best effort implication of target features by custom cfg #145810

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Stabilize 29 RISC-V target features (riscv_ratified_v2) #145948

Stabilize 29 RISC-V target features (riscv_ratified_v2) #145948

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Consideration: Feature Naming (for std_detect)

Consideration: Deferring to Version 1.92 Cycle may Have its Benefit

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Stabilize 29 RISC-V target features (`riscv_ratified_v2`) #145948

Stabilize 29 RISC-V target features (`riscv_ratified_v2`) #145948

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Consideration: Feature Naming (for `std_detect`)