Have the alignment intrinsics return ptr::Alignment directly

[scottmcm]

View all comments

Follow-up to #152605

Notably, a common case of align_of_val is to put it in Layout for allocator calls, so might as well have it just be an Alignment already to avoid the extra transmute.

No changes to rustc_const_eval because that's already writing a Scalar into a place, which does what we need since ptr::Alignment is repr(transparent) to a repr(usize).

[scottmcm]

I don't think anything in here should be more expensive, but in case...
@bors try @rust-timer queue

[rust-bors]

☀️ Try build successful (CI)
Build commit: 7121e2d (7121e2d136c08d87b9a5f3717916d4bec53334bb, parent: 2219766af622ad1f051ca96ae40650106b1bd9bd)

[rust-timer]

Finished benchmarking commit (7121e2d): comparison URL.

Overall result: ❌✅ regressions and improvements - please read the text below

Benchmarking this pull request means it may be perf-sensitive – we'll automatically label it not fit for rolling up. You can override this, but we strongly advise not to, due to possible changes in compiler perf.

Next Steps: If you can justify the regressions found in this try perf run, please do so in sufficient writing along with @rustbot label: +perf-regression-triaged. If not, please fix the regressions and do another perf run. If its results are neutral or positive, the label will be automatically removed.

@bors rollup=never
@rustbot label: -S-waiting-on-perf +perf-regression

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)	4.5%	[0.2%, 16.2%]	4
Regressions ❌ (secondary)	0.6%	[0.3%, 0.9%]	2
Improvements ✅ (primary)	-0.4%	[-1.2%, -0.2%]	7
Improvements ✅ (secondary)	-1.0%	[-3.3%, -0.1%]	22
All ❌✅ (primary)	1.4%	[-1.2%, 16.2%]	11

Max RSS (memory usage)

Results (primary -3.9%, secondary 2.9%)

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)	5.2%	[1.3%, 9.0%]	2
Improvements ✅ (primary)	-3.9%	[-5.4%, -1.6%]	5
Improvements ✅ (secondary)	-1.7%	[-1.7%, -1.7%]	1
All ❌✅ (primary)	-3.9%	[-5.4%, -1.6%]	5

Cycles

Results (primary 11.9%, secondary -1.7%)

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

	mean	range	count
Regressions ❌ (primary)	11.9%	[11.9%, 11.9%]	1
Regressions ❌ (secondary)	4.0%	[4.0%, 4.0%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-3.1%	[-4.8%, -2.2%]	4
All ❌✅ (primary)	11.9%	[11.9%, 11.9%]	1

Binary size

Results (primary 0.3%, secondary -0.8%)

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

	mean	range	count
Regressions ❌ (primary)	0.6%	[0.0%, 1.4%]	14
Regressions ❌ (secondary)	0.2%	[0.0%, 0.4%]	8
Improvements ✅ (primary)	-0.5%	[-0.7%, -0.1%]	4
Improvements ✅ (secondary)	-1.3%	[-2.2%, -0.4%]	17
All ❌✅ (primary)	0.3%	[-0.7%, 1.4%]	18

Bootstrap: 485.129s -> 482.811s (-0.48%)
Artifact size: 398.01 MiB -> 396.01 MiB (-0.50%)

[scottmcm]

r? @cjgillot
@rustbot ready

Those perf results are, I think, overall good. They're mostly green, and include things like -28% on rustc_mir_build, which is impressively good.

The one big regression is one of the LTO sub-jobs just going nuts for some reason:

TBH I'm not sure how this could possibly cause that. It's not the kind of "oh, inlining reshuffled everything" that we normally see from MIR changes. None of the other variants of that code show any material impact, and it's just so different from the results on everything else.

[rustbot]

Some changes occurred in compiler/rustc_codegen_gcc

cc @antoyo, @GuillaumeGomez

Some changes occurred in compiler/rustc_codegen_cranelift

cc @bjorn3

Some changes occurred to MIR optimizations

cc @rust-lang/wg-mir-opt

This PR modifies tests/auxiliary/minicore.rs.

cc @jieyouxu

Some changes occurred to the intrinsics. Make sure the CTFE / Miri interpreter
gets adapted for the changes, if necessary.

cc @rust-lang/miri, @RalfJung, @oli-obk, @lcnr

[scottmcm]

@bors try @rust-timer queue

[rust-bors]

☀️ Try build successful (CI)
Build commit: a606286 (a60628660b41f808eeed74cac626bfc49b619ef6, parent: 4a997eeefbb8cf41617324bb6d08c72171c614e2)

[rust-timer]

Finished benchmarking commit (a606286): comparison URL.

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

Benchmarking means the PR may be perf-sensitive. It's automatically marked not fit for rolling up. Overriding is possible but disadvised: it risks changing compiler perf.

Next, please: If you can, justify the regressions found in this try perf run in writing along with @rustbot label: +perf-regression-triaged. If not, fix the regressions and do another perf run. Neutral or positive results will clear the label automatically.

@bors rollup=never
@rustbot label: -S-waiting-on-perf +perf-regression

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)	15.9%	[15.9%, 15.9%]	1
Regressions ❌ (secondary)	0.2%	[0.2%, 0.2%]	2
Improvements ✅ (primary)	-0.4%	[-0.5%, -0.3%]	3
Improvements ✅ (secondary)	-1.3%	[-3.9%, -0.2%]	17
All ❌✅ (primary)	3.7%	[-0.5%, 15.9%]	4

Max RSS (memory usage)

Results (primary -0.0%, secondary -3.5%)

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

	mean	range	count
Regressions ❌ (primary)	2.5%	[2.3%, 2.7%]	3
Regressions ❌ (secondary)	0.9%	[0.9%, 0.9%]	1
Improvements ✅ (primary)	-2.0%	[-2.7%, -0.8%]	4
Improvements ✅ (secondary)	-4.9%	[-9.3%, -2.6%]	3
All ❌✅ (primary)	-0.0%	[-2.7%, 2.7%]	7

Cycles

Results (primary 11.9%, secondary -3.1%)

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

	mean	range	count
Regressions ❌ (primary)	11.9%	[11.9%, 11.9%]	1
Regressions ❌ (secondary)	3.2%	[3.2%, 3.2%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-4.0%	[-5.1%, -2.4%]	7
All ❌✅ (primary)	11.9%	[11.9%, 11.9%]	1

Binary size

Results (primary 0.2%, secondary -0.5%)

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

	mean	range	count
Regressions ❌ (primary)	0.4%	[0.0%, 1.4%]	26
Regressions ❌ (secondary)	0.2%	[0.0%, 0.4%]	12
Improvements ✅ (primary)	-0.1%	[-0.4%, -0.0%]	16
Improvements ✅ (secondary)	-1.0%	[-2.6%, -0.0%]	18
All ❌✅ (primary)	0.2%	[-0.4%, 1.4%]	42

Bootstrap: 497.359s -> 498.748s (0.28%)
Artifact size: 397.13 MiB -> 397.19 MiB (0.02%)

[rust-log-analyzer]

The job aarch64-gnu-llvm-21-1 failed! Check out the build log: (web) (plain enhanced) (plain)

Click to see the possible cause of the failure (guessed by this bot)

Executing "/scripts/stage_2_test_set1.sh"
+ /scripts/stage_2_test_set1.sh
PR_CI_JOB set; skipping tidy
+ '[' 1 == 1 ']'
+ echo 'PR_CI_JOB set; skipping tidy'
+ SKIP_TIDY='--skip tidy'
+ ../x.py --stage 2 test --skip tidy --skip compiler --skip src
##[group]Building bootstrap
    Finished `dev` profile [unoptimized] target(s) in 0.04s
##[endgroup]
downloading https://static.rust-lang.org/dist/2026-04-14/rustfmt-nightly-aarch64-unknown-linux-gnu.tar.xz
---
---- [ui] tests/ui/consts/const-size_of_val-align_of_val-extern-type.rs stdout ----
Saved the actual stderr to `/checkout/obj/build/aarch64-unknown-linux-gnu/test/ui/consts/const-size_of_val-align_of_val-extern-type/const-size_of_val-align_of_val-extern-type.stderr`
diff of stderr:

+ warning: use of deprecated type alias `std::ptr::Alignment`: moved from `ptr` to `mem`
+   --> $DIR/const-size_of_val-align_of_val-extern-type.rs:6:15
+    |
+ LL | use std::ptr::Alignment;
+    |               ^^^^^^^^^
+    |
+    = note: `#[warn(deprecated)]` on by default
+ 
+ warning: use of deprecated type alias `std::ptr::Alignment`: moved from `ptr` to `mem`
+   --> $DIR/const-size_of_val-align_of_val-extern-type.rs:14:15
+    |
+ LL | const _ALIGN: Alignment = unsafe { align_of_val(&4 as *const i32 as *const Opaque) };
+    |               ^^^^^^^^^
+ 
1 error[E0277]: the size for values of type `Opaque` cannot be known
2   --> $DIR/const-size_of_val-align_of_val-extern-type.rs:12:43
3    |

34 LL | const _ALIGN: Alignment = unsafe { align_of_val(&mut (&4 as *const i32 as *const Opaque)) };
35    |                                                 ++++++                                 +
36 
- error: aborting due to 2 previous errors
+ error: aborting due to 2 previous errors; 2 warnings emitted
38 
39 For more information about this error, try `rustc --explain E0277`.
40 

Note: some mismatched output was normalized before being compared
-   --> /checkout/tests/ui/consts/const-size_of_val-align_of_val-extern-type.rs:6:15
-   --> /checkout/tests/ui/consts/const-size_of_val-align_of_val-extern-type.rs:14:15
+ warning: use of deprecated type alias `std::ptr::Alignment`: moved from `ptr` to `mem`
+   --> $DIR/const-size_of_val-align_of_val-extern-type.rs:6:15
+    |
+ LL | use std::ptr::Alignment;
+    |               ^^^^^^^^^
+    |
+    = note: `#[warn(deprecated)]` on by default
+ 
+ warning: use of deprecated type alias `std::ptr::Alignment`: moved from `ptr` to `mem`
+   --> $DIR/const-size_of_val-align_of_val-extern-type.rs:14:15
+    |
+ LL | const _ALIGN: Alignment = unsafe { align_of_val(&4 as *const i32 as *const Opaque) };
+    |               ^^^^^^^^^
+ 
+ error: aborting due to 2 previous errors; 2 warnings emitted


The actual stderr differed from the expected stderr
To update references, rerun the tests and pass the `--bless` flag
To only update this specific test, also pass `--test-args consts/const-size_of_val-align_of_val-extern-type.rs`

error: 1 errors occurred comparing output.
status: exit status: 1
command: env -u RUSTC_LOG_COLOR RUSTC_ICE="0" RUST_BACKTRACE="short" "/checkout/obj/build/aarch64-unknown-linux-gnu/stage2/bin/rustc" "/checkout/tests/ui/consts/const-size_of_val-align_of_val-extern-type.rs" "-Zthreads=1" "-Zsimulate-remapped-rust-src-base=/rustc/FAKE_PREFIX" "-Ztranslate-remapped-path-to-local-path=no" "-Z" "ignore-directory-in-diagnostics-source-blocks=/cargo" "-Z" "ignore-directory-in-diagnostics-source-blocks=/checkout/vendor" "--sysroot" "/checkout/obj/build/aarch64-unknown-linux-gnu/stage2" "--target=aarch64-unknown-linux-gnu" "--check-cfg" "cfg(test,FALSE)" "--error-format" "json" "--json" "future-incompat" "-Ccodegen-units=1" "-Zui-testing" "-Zdeduplicate-diagnostics=no" "-Zwrite-long-types-to-disk=no" "-Cstrip=debuginfo" "--emit" "metadata" "-C" "prefer-dynamic" "--out-dir" "/checkout/obj/build/aarch64-unknown-linux-gnu/test/ui/consts/const-size_of_val-align_of_val-extern-type" "-A" "unused" "-W" "unused_attributes" "-A" "internal_features" "-A" "incomplete_features" "-A" "unused_parens" "-A" "unused_braces" "-Crpath" "-Cdebuginfo=0" "-Lnative=/checkout/obj/build/aarch64-unknown-linux-gnu/native/rust-test-helpers"
stdout: none
--- stderr -------------------------------
warning: use of deprecated type alias `std::ptr::Alignment`: moved from `ptr` to `mem`
##[warning]  --> /checkout/tests/ui/consts/const-size_of_val-align_of_val-extern-type.rs:6:15
   |
---

warning: use of deprecated type alias `std::ptr::Alignment`: moved from `ptr` to `mem`
##[warning]  --> /checkout/tests/ui/consts/const-size_of_val-align_of_val-extern-type.rs:14:15
   |
LL | const _ALIGN: Alignment = unsafe { align_of_val(&4 as *const i32 as *const Opaque) };
   |               ^^^^^^^^^

error[E0277]: the size for values of type `Opaque` cannot be known
##[error]  --> /checkout/tests/ui/consts/const-size_of_val-align_of_val-extern-type.rs:12:43
   |
LL | const _SIZE: usize = unsafe { size_of_val(&4 as *const i32 as *const Opaque) };
   |                               ----------- ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `MetaSized` is not implemented for `Opaque`
   |                               |
   |                               required by a bound introduced by this call
   |
   = note: the trait bound `Opaque: MetaSized` is not satisfied
note: required by a bound in `std::intrinsics::size_of_val`
  --> /rustc/FAKE_PREFIX/library/core/src/intrinsics/mod.rs:2861:0
help: consider borrowing here
   |
LL | const _SIZE: usize = unsafe { size_of_val(&(&4 as *const i32 as *const Opaque)) };
   |                                           ++                                 +
LL | const _SIZE: usize = unsafe { size_of_val(&mut (&4 as *const i32 as *const Opaque)) };
   |                                           ++++++                                 +

error[E0277]: the size for values of type `Opaque` cannot be known
##[error]  --> /checkout/tests/ui/consts/const-size_of_val-align_of_val-extern-type.rs:14:49
   |
LL | const _ALIGN: Alignment = unsafe { align_of_val(&4 as *const i32 as *const Opaque) };
   |                                    ------------ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `MetaSized` is not implemented for `Opaque`
   |                                    |
   |                                    required by a bound introduced by this call
   |
   = note: the trait bound `Opaque: MetaSized` is not satisfied
note: required by a bound in `std::intrinsics::align_of_val`
  --> /rustc/FAKE_PREFIX/library/core/src/intrinsics/mod.rs:2874:0
help: consider borrowing here
   |
LL | const _ALIGN: Alignment = unsafe { align_of_val(&(&4 as *const i32 as *const Opaque)) };
   |                                                 ++                                 +
LL | const _ALIGN: Alignment = unsafe { align_of_val(&mut (&4 as *const i32 as *const Opaque)) };
   |                                                 ++++++                                 +

error: aborting due to 2 previous errors; 2 warnings emitted

For more information about this error, try `rustc --explain E0277`.
---
Saved the actual stderr to `/checkout/obj/build/aarch64-unknown-linux-gnu/test/ui/consts/const-unstable-intrinsic/const-unstable-intrinsic.stderr`
diff of stderr:

18    = help: add `#![feature(unstable)]` to the crate attributes to enable
19    = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
20 
+ warning: use of deprecated type alias `std::ptr::Alignment`: moved from `ptr` to `mem`
+   --> $DIR/const-unstable-intrinsic.rs:38:63
+    |
+ LL | pub const unsafe fn align_of_val<T>(x: *const T) -> std::ptr::Alignment;
+    |                                                               ^^^^^^^^^
+    |
+    = note: `#[warn(deprecated)]` on by default
+ 
21 error: `size_of_val` is not yet stable as a const intrinsic
22   --> $DIR/const-unstable-intrinsic.rs:17:9
23    |

84 LL |     const unsafe fn copy<T>(src: *const T, _dst: *mut T, _count: usize) {
85    |
86 
- error: aborting due to 8 previous errors
+ error: aborting due to 8 previous errors; 1 warning emitted
88 
89 For more information about this error, try `rustc --explain E0658`.
90 

Note: some mismatched output was normalized before being compared
-   --> /checkout/tests/ui/consts/const-unstable-intrinsic.rs:38:63
+ warning: use of deprecated type alias `std::ptr::Alignment`: moved from `ptr` to `mem`
+   --> $DIR/const-unstable-intrinsic.rs:38:63
+    |
+ LL | pub const unsafe fn align_of_val<T>(x: *const T) -> std::ptr::Alignment;
+    |                                                               ^^^^^^^^^
+    |
+    = note: `#[warn(deprecated)]` on by default
+ 
+ error: aborting due to 8 previous errors; 1 warning emitted
---
To only update this specific test, also pass `--test-args consts/const-unstable-intrinsic.rs`

error: 1 errors occurred comparing output.
status: exit status: 1
command: env -u RUSTC_LOG_COLOR RUSTC_ICE="0" RUST_BACKTRACE="short" "/checkout/obj/build/aarch64-unknown-linux-gnu/stage2/bin/rustc" "/checkout/tests/ui/consts/const-unstable-intrinsic.rs" "-Zthreads=1" "-Zsimulate-remapped-rust-src-base=/rustc/FAKE_PREFIX" "-Ztranslate-remapped-path-to-local-path=no" "-Z" "ignore-directory-in-diagnostics-source-blocks=/cargo" "-Z" "ignore-directory-in-diagnostics-source-blocks=/checkout/vendor" "--sysroot" "/checkout/obj/build/aarch64-unknown-linux-gnu/stage2" "--target=aarch64-unknown-linux-gnu" "--check-cfg" "cfg(test,FALSE)" "--error-format" "json" "--json" "future-incompat" "-Ccodegen-units=1" "-Zui-testing" "-Zdeduplicate-diagnostics=no" "-Zwrite-long-types-to-disk=no" "-Cstrip=debuginfo" "--emit" "metadata" "-C" "prefer-dynamic" "--out-dir" "/checkout/obj/build/aarch64-unknown-linux-gnu/test/ui/consts/const-unstable-intrinsic" "-A" "unused" "-W" "unused_attributes" "-A" "internal_features" "-A" "incomplete_features" "-A" "unused_parens" "-A" "unused_braces" "-Crpath" "-Cdebuginfo=0" "-Lnative=/checkout/obj/build/aarch64-unknown-linux-gnu/native/rust-test-helpers" "-L" "/checkout/obj/build/aarch64-unknown-linux-gnu/test/ui/consts/const-unstable-intrinsic/auxiliary"
stdout: none
--- stderr -------------------------------
error[E0658]: use of unstable library feature `unstable`
##[error]  --> /checkout/tests/ui/consts/const-unstable-intrinsic.rs:17:9
   |
LL |         unstable_intrinsic::size_of_val(&x);
   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: see issue #42 <https://github.com/rust-lang/rust/issues/42> for more information
   = help: add `#![feature(unstable)]` to the crate attributes to enable
   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date

error[E0658]: use of unstable library feature `unstable`
##[error]  --> /checkout/tests/ui/consts/const-unstable-intrinsic.rs:20:9
   |
LL |         unstable_intrinsic::align_of_val(&x);
   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: see issue #42 <https://github.com/rust-lang/rust/issues/42> for more information
   = help: add `#![feature(unstable)]` to the crate attributes to enable
   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date

warning: use of deprecated type alias `std::ptr::Alignment`: moved from `ptr` to `mem`
##[warning]  --> /checkout/tests/ui/consts/const-unstable-intrinsic.rs:38:63
   |
LL | pub const unsafe fn align_of_val<T>(x: *const T) -> std::ptr::Alignment;
   |                                                               ^^^^^^^^^
   |
   = note: `#[warn(deprecated)]` on by default

error: `size_of_val` is not yet stable as a const intrinsic
---
   |
LL + #![feature(unstable)]
   |

error: const function that might be (indirectly) exposed to stable cannot use `#[feature(local)]`
##[error]  --> /checkout/tests/ui/consts/const-unstable-intrinsic.rs:24:9
   |
LL |         size_of_val(&x);
   |         ^^^^^^^^^^^^^^^
   |
help: if the function is not (yet) meant to be exposed to stable const contexts, add `#[rustc_const_unstable]`
   |
LL + #[rustc_const_unstable(feature = "...", issue = "...")]
LL | const fn const_main() {
   |

error: const function that might be (indirectly) exposed to stable cannot use `#[feature(local)]`
##[error]  --> /checkout/tests/ui/consts/const-unstable-intrinsic.rs:26:9
   |
LL |         align_of_val(&x);
   |         ^^^^^^^^^^^^^^^^
   |
help: if the function is not (yet) meant to be exposed to stable const contexts, add `#[rustc_const_unstable]`
   |
LL + #[rustc_const_unstable(feature = "...", issue = "...")]
LL | const fn const_main() {
   |

error: intrinsic `copy::copy` cannot be (indirectly) exposed to stable
##[error]  --> /checkout/tests/ui/consts/const-unstable-intrinsic.rs:48:14
   |
LL |     unsafe { copy(src, dst, count) }
   |              ^^^^^^^^^^^^^^^^^^^^^
   |
   = help: mark the caller as `#[rustc_const_unstable]`, or mark the intrinsic `#[rustc_intrinsic_const_stable_indirect]` (but this requires team approval)

error: const function that might be (indirectly) exposed to stable cannot use `#[feature(local)]`
##[error]  --> /checkout/tests/ui/consts/const-unstable-intrinsic.rs:56:9
   |
LL |         super::size_of_val(src);
   |         ^^^^^^^^^^^^^^^^^^^^^^^
   |
help: if the function is not (yet) meant to be exposed to stable const contexts, add `#[rustc_const_unstable]`
   |
LL +     #[rustc_const_unstable(feature = "...", issue = "...")]
LL |     const unsafe fn copy<T>(src: *const T, _dst: *mut T, _count: usize) {
   |

error: aborting due to 8 previous errors; 1 warning emitted

For more information about this error, try `rustc --explain E0658`.