Gate `z` inline asm template modifier by lqd · Pull Request #165083 · rust-lang/rust

lqd · 2026-10-28T14:21:22Z

This PR fixes an unexpected side-effect of #158312, as shown in #165055: the z template modifier is accepted on nightly and beta without needing the asm_experimental_reg gate enabled, and this would unexpectedly become stable in the next release.

This PR fixes that, with some diagnostics pointing at the feature gate instead of just rejecting the template modifier (the latter can be seen in the second commit).

Fixes (after beta backport) #165055.

as shown in issue 165055, an unstable use of the `z` modifier should be rejected. That would make this test fail, but it doesn't yet.

…_reg` This also correctly rejects the previous test. The other tests relying on the modifier are changed to enable the feature.

This improves the error when using the `z` template modifier on stable, pointing towards the expected feature gate to enable it.

rustbot · 2026-10-28T14:21:29Z

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davidtwco · 2026-10-28T14:44:10Z

r? @davidtwco

r=me when CI passes

lqd · 2026-10-28T15:52:21Z

@bors r=davidtwco

#158312 will land in 1.100, fixing #165055 will thus need a backport.

backport context: a simple change to prevent an accidental stabilization.
@rustbot label +beta-nominated

rust-bors · 2026-10-28T15:52:25Z

📌 Commit fd05e39 has been approved by davidtwco

It is now in the queue for this repository.

Gate `z` inline asm template modifier This PR fixes an unexpected side-effect of rust-lang#158312, as shown in rust-lang#165055: the `z` template modifier is accepted on nightly and beta without needing the `asm_experimental_reg` gate enabled, and this would unexpectedly become stable in the next release. This PR fixes that, with some diagnostics pointing at the feature gate instead of just rejecting the template modifier (the latter can be seen in the second commit). Fixes (after beta backport) rust-lang#165055.

…uwer Rollup of 22 pull requests Successful merges: - #165032 (stdarch subtree update) - #165072 (Submodule update of rustc-perf) - #144090 (Make `IoSlice` and `IoSliceMut` methods unstably const) - #162342 (More stdarch regression tests) - #163909 (std: Test the exit behavior of `abort` and `abort_immediate`) - #164766 (Unstably introduce MVP edition migration lint `unmarked_unchecked_type_aliases` together with bikeshed attribute `#[rustc_unchecked_type_alias]`) - #164916 (CI: rfl: move job forward to Linux v7.3) - #164924 (Remove `TypeKind` from `rustc_codegen_ssa`) - #164969 (perf: avoid allocating HashSet in is_distinct check on small SwitchInts) - #165083 (Gate `z` inline asm template modifier) - #165087 (Fix flaky CI test `named_temp_file_new_creates_file`) - #161131 (Check associated const binding types) - #161418 (give next-solver's `evaluate_const` its own `try_evaluate_const` logic) - #164315 (make powerpc `Complex` ABI GCC-compatible) - #164476 (Avoid ICE on None from prepare_vtable_segments) - #164981 (Reflection add TypeId::name) - #165003 (follow up for global-alloc-reentry test) - #165020 (Bless mir-opt panic-abort tests) - #165066 (skip max_repr_align in Layout::eq_abi) - #165080 (Syntactically allow C-variadics in parenthesized argument lists) - #165081 (move `#[rustc_allow_const_fn_unstable]` attr check to attr parsing stage) - #165082 (Remove stability note from `rust_splat`)

Gate `z` inline asm template modifier This PR fixes an unexpected side-effect of rust-lang#158312, as shown in rust-lang#165055: the `z` template modifier is accepted on nightly and beta without needing the `asm_experimental_reg` gate enabled, and this would unexpectedly become stable in the next release. This PR fixes that, with some diagnostics pointing at the feature gate instead of just rejecting the template modifier (the latter can be seen in the second commit). Fixes (after beta backport) rust-lang#165055.

…uwer Rollup of 23 pull requests Successful merges: - #165032 (stdarch subtree update) - #165072 (Submodule update of rustc-perf) - #144090 (Make `IoSlice` and `IoSliceMut` methods unstably const) - #162342 (More stdarch regression tests) - #163909 (std: Test the exit behavior of `abort` and `abort_immediate`) - #164766 (Unstably introduce MVP edition migration lint `unmarked_unchecked_type_aliases` together with bikeshed attribute `#[rustc_unchecked_type_alias]`) - #164916 (CI: rfl: move job forward to Linux v7.3) - #164924 (Remove `TypeKind` from `rustc_codegen_ssa`) - #164969 (perf: avoid allocating HashSet in is_distinct check on small SwitchInts) - #165083 (Gate `z` inline asm template modifier) - #165087 (Fix flaky CI test `named_temp_file_new_creates_file`) - #165123 (Temporarily drop macos-26 jobs) - #161131 (Check associated const binding types) - #161418 (give next-solver's `evaluate_const` its own `try_evaluate_const` logic) - #164315 (make powerpc `Complex` ABI GCC-compatible) - #164476 (Avoid ICE on None from prepare_vtable_segments) - #164981 (Reflection add TypeId::name) - #165003 (follow up for global-alloc-reentry test) - #165020 (Bless mir-opt panic-abort tests) - #165066 (skip max_repr_align in Layout::eq_abi) - #165080 (Syntactically allow C-variadics in parenthesized argument lists) - #165081 (move `#[rustc_allow_const_fn_unstable]` attr check to attr parsing stage) - #165082 (Remove stability note from `rust_splat`)

…uwer Rollup of 22 pull requests Successful merges: - #165032 (stdarch subtree update) - #165123 (Temporarily drop macos-26 jobs) - #165072 (Submodule update of rustc-perf) - #144090 (Make `IoSlice` and `IoSliceMut` methods unstably const) - #162342 (More stdarch regression tests) - #163909 (std: Test the exit behavior of `abort` and `abort_immediate`) - #164766 (Unstably introduce MVP edition migration lint `unmarked_unchecked_type_aliases` together with bikeshed attribute `#[rustc_unchecked_type_alias]`) - #164916 (CI: rfl: move job forward to Linux v7.3) - #164924 (Remove `TypeKind` from `rustc_codegen_ssa`) - #164969 (perf: avoid allocating HashSet in is_distinct check on small SwitchInts) - #165083 (Gate `z` inline asm template modifier) - #165087 (Fix flaky CI test `named_temp_file_new_creates_file`) - #161131 (Check associated const binding types) - #161418 (give next-solver's `evaluate_const` its own `try_evaluate_const` logic) - #164315 (make powerpc `Complex` ABI GCC-compatible) - #164476 (Avoid ICE on None from prepare_vtable_segments) - #165003 (follow up for global-alloc-reentry test) - #165020 (Bless mir-opt panic-abort tests) - #165066 (skip max_repr_align in Layout::eq_abi) - #165080 (Syntactically allow C-variadics in parenthesized argument lists) - #165081 (move `#[rustc_allow_const_fn_unstable]` attr check to attr parsing stage) - #165082 (Remove stability note from `rust_splat`)

Rollup merge of #165083 - lqd:sve-gate, r=davidtwco Gate `z` inline asm template modifier This PR fixes an unexpected side-effect of #158312, as shown in #165055: the `z` template modifier is accepted on nightly and beta without needing the `asm_experimental_reg` gate enabled, and this would unexpectedly become stable in the next release. This PR fixes that, with some diagnostics pointing at the feature gate instead of just rejecting the template modifier (the latter can be seen in the second commit). Fixes (after beta backport) #165055.

rust-timer · 2026-10-30T04:31:39Z

Note

This PR was benchmarked as part of triage of its containing rollup: triage URL.

Finished benchmarking commit (58d9fe1): comparison URL.

Overall result: ❌✅ regressions and improvements - please read:

Our benchmarks found a performance regression caused by this PR.
This might be an actual regression, but it can also be just noise.

Next Steps:

If the regression was expected or you think it can be justified,
please write a comment with sufficient written justification, and add
@rustbot label: +perf-regression-triaged to it, to mark the regression as triaged.
If you think that you know of a way to resolve the regression, try to create
a new PR with a fix for the regression.
If you do not understand the regression or you think that it is just noise,
you can ask the @rust-lang/wg-compiler-performance working group for help (members of this group
were already notified of this PR).

@rustbot label: +perf-regression
cc @rust-lang/wg-compiler-performance

Instruction count

Our most reliable metric. Used to determine the overall result above. However, even this metric can be noisy.

	mean	range	count
Regressions ❌ (primary)	0.2%	[0.1%, 0.2%]	5
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-0.2%	[-0.3%, -0.2%]	16
All ❌✅ (primary)	0.2%	[0.1%, 0.2%]	5

Max RSS (memory usage)

Results (secondary 2.4%)

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)	2.4%	[2.4%, 2.4%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Cycles

Results (primary 2.4%)

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

	mean	range	count
Regressions ❌ (primary)	2.4%	[2.4%, 2.4%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	2.4%	[2.4%, 2.4%]	1

Binary size

This perf run didn't have relevant results for this metric.

Artifact size: 406.68 MiB -> 406.87 MiB (0.05%)

…uwer Rollup of 22 pull requests Successful merges: - rust-lang/rust#165032 (stdarch subtree update) - rust-lang/rust#165123 (Temporarily drop macos-26 jobs) - rust-lang/rust#165072 (Submodule update of rustc-perf) - rust-lang/rust#144090 (Make `IoSlice` and `IoSliceMut` methods unstably const) - rust-lang/rust#162342 (More stdarch regression tests) - rust-lang/rust#163909 (std: Test the exit behavior of `abort` and `abort_immediate`) - rust-lang/rust#164766 (Unstably introduce MVP edition migration lint `unmarked_unchecked_type_aliases` together with bikeshed attribute `#[rustc_unchecked_type_alias]`) - rust-lang/rust#164916 (CI: rfl: move job forward to Linux v7.3) - rust-lang/rust#164924 (Remove `TypeKind` from `rustc_codegen_ssa`) - rust-lang/rust#164969 (perf: avoid allocating HashSet in is_distinct check on small SwitchInts) - rust-lang/rust#165083 (Gate `z` inline asm template modifier) - rust-lang/rust#165087 (Fix flaky CI test `named_temp_file_new_creates_file`) - rust-lang/rust#161131 (Check associated const binding types) - rust-lang/rust#161418 (give next-solver's `evaluate_const` its own `try_evaluate_const` logic) - rust-lang/rust#164315 (make powerpc `Complex` ABI GCC-compatible) - rust-lang/rust#164476 (Avoid ICE on None from prepare_vtable_segments) - rust-lang/rust#165003 (follow up for global-alloc-reentry test) - rust-lang/rust#165020 (Bless mir-opt panic-abort tests) - rust-lang/rust#165066 (skip max_repr_align in Layout::eq_abi) - rust-lang/rust#165080 (Syntactically allow C-variadics in parenthesized argument lists) - rust-lang/rust#165081 (move `#[rustc_allow_const_fn_unstable]` attr check to attr parsing stage) - rust-lang/rust#165082 (Remove stability note from `rust_splat`)

rustbot · 2026-11-02T09:52:44Z

beta backport approved as per compiler team on Zulip. A backport PR will be authored by the release team at the end of the current development cycle. Backport labels are handled by them.

…uwer Rollup of 22 pull requests Successful merges: - rust-lang/rust#165032 (stdarch subtree update) - rust-lang/rust#165123 (Temporarily drop macos-26 jobs) - rust-lang/rust#165072 (Submodule update of rustc-perf) - rust-lang/rust#144090 (Make `IoSlice` and `IoSliceMut` methods unstably const) - rust-lang/rust#162342 (More stdarch regression tests) - rust-lang/rust#163909 (std: Test the exit behavior of `abort` and `abort_immediate`) - rust-lang/rust#164766 (Unstably introduce MVP edition migration lint `unmarked_unchecked_type_aliases` together with bikeshed attribute `#[rustc_unchecked_type_alias]`) - rust-lang/rust#164916 (CI: rfl: move job forward to Linux v7.3) - rust-lang/rust#164924 (Remove `TypeKind` from `rustc_codegen_ssa`) - rust-lang/rust#164969 (perf: avoid allocating HashSet in is_distinct check on small SwitchInts) - rust-lang/rust#165083 (Gate `z` inline asm template modifier) - rust-lang/rust#165087 (Fix flaky CI test `named_temp_file_new_creates_file`) - rust-lang/rust#161131 (Check associated const binding types) - rust-lang/rust#161418 (give next-solver's `evaluate_const` its own `try_evaluate_const` logic) - rust-lang/rust#164315 (make powerpc `Complex` ABI GCC-compatible) - rust-lang/rust#164476 (Avoid ICE on None from prepare_vtable_segments) - rust-lang/rust#165003 (follow up for global-alloc-reentry test) - rust-lang/rust#165020 (Bless mir-opt panic-abort tests) - rust-lang/rust#165066 (skip max_repr_align in Layout::eq_abi) - rust-lang/rust#165080 (Syntactically allow C-variadics in parenthesized argument lists) - rust-lang/rust#165081 (move `#[rustc_allow_const_fn_unstable]` attr check to attr parsing stage) - rust-lang/rust#165082 (Remove stability note from `rust_splat`)

[beta] backports - [beta] Revert "riscv: stabilize 'd' and 'f' target features" #165333 - [rustdoc] Move the creation of `IndividualTestOptions` into the test runner closure to ensure the temporary folder is removed right after the test is done running #164202 - rustdoc: don't panic on a nested use group with no path prefix #164883 - Gate `z` inline asm template modifier #165083 - Fix ICE in prelude edition lint #165129 - Update LLVM submodule #165133 r? me

[beta] backports - [beta] Revert "riscv: stabilize 'd' and 'f' target features" #165333 - [rustdoc] Move the creation of `IndividualTestOptions` into the test runner closure to ensure the temporary folder is removed right after the test is done running #164202 - rustdoc: don't panic on a nested use group with no path prefix #164883 - Gate `z` inline asm template modifier #165083 - Fix ICE in prelude edition lint #165129 - Update LLVM submodule #165133 - [beta] Revert "Fixes adjustment of `max_width` within macros" (rust-lang/rustfmt#6651) and follow-up (rust-lang/rustfmt#7152) #165380 r? me

JonathanBrouwer · 2026-11-03T10:36:12Z

@rustbot label: +perf-regression-triaged
Noise

lqd added 3 commits October 28, 2026 15:07

add test showing the problem

d9d743e

as shown in issue 165055, an unstable use of the `z` modifier should be rejected. That would make this test fail, but it doesn't yet.

ensure the z asm template modifier is gated under `asm_experimental…

6dc606c

…_reg` This also correctly rejects the previous test. The other tests relying on the modifier are changed to enable the feature.

introduce unstable template modifier diagnostic variant

fd05e39

This improves the error when using the `z` template modifier on stable, pointing towards the expected feature gate to enable it.

rustbot assigned beetrees Oct 28, 2026

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. labels Oct 28, 2026

davidtwco approved these changes Oct 28, 2026

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rustbot assigned davidtwco and unassigned beetrees Oct 28, 2026

rustbot added the beta-nominated Nominated for backporting to the compiler in the beta channel. label Oct 28, 2026

rust-bors Bot 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 Oct 28, 2026

lqd mentioned this pull request Oct 28, 2026

Accidental stabilization of z template modifiers #165055

Closed

JonathanBrouwer mentioned this pull request Oct 28, 2026

Rollup of 22 pull requests #165095

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JonathanBrouwer mentioned this pull request Oct 29, 2026

Rollup of 23 pull requests #165130

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JonathanBrouwer mentioned this pull request Oct 29, 2026

Rollup of 22 pull requests #165151

Merged

rust-bors Bot merged commit ee5a328 into rust-lang:main Oct 29, 2026
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rustbot added this to the 1.101.0 milestone Oct 29, 2026

rustbot added the perf-regression Performance regression. label Oct 30, 2026

lqd deleted the sve-gate branch November 2, 2026 09:49

rustbot added the beta-accepted Accepted for backporting to the compiler in the beta channel. label Nov 2, 2026

cuviper mentioned this pull request Nov 2, 2026

[beta] backports #165368

Merged

cuviper modified the milestones: 1.101.0, 1.100.0 Nov 2, 2026

cuviper removed the beta-nominated Nominated for backporting to the compiler in the beta channel. label Nov 2, 2026

rustbot added the perf-regression-triaged The performance regression has been triaged. label Nov 3, 2026

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Gate `z` inline asm template modifier - #165083

Gate `z` inline asm template modifier#165083
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Overall result: ❌✅ regressions and improvements - please read:

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