raw_vec.rs: Remove superfluous fn alloc_guard #145750

btj · 2025-08-22T13:37:41Z

alloc_guard checks that its argument is at most isize::MAX, but it is called only with layout sizes, which are already guaranteed to be at most isize::MAX.

btj · 2025-08-22T13:41:22Z

I discovered this issue while writing a description of the proof I developed for AWS Rust Standard Library Verification Contest Challenge 19.

rustbot · 2025-08-22T18:16:24Z

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samueltardieu · 2025-08-27T07:14:11Z

Isn't alloc_guard() the guarantee that the layout size doesn't exceed isize::MAX? Isn't there a call chain such as this one?

RawVec<T, Global>::with_capacity(u) where u is a usize
RawVecInner<Global>::with_capacity(u, T::LAYOUT)
RawVecInner::try_allocate_in(u, T::LAYOUT) which guards against overcapacity by calling alloc_guard()

btj · 2025-08-27T07:37:08Z

No, this check already happens earlier in try_allocate_in, in the call of layout_array, which in turn calls Layout::repeat, which fails if the layout size would exceed isize::MAX. Because it is an invariant of Layout that the size is at most isize::MAX.

samueltardieu · 2025-08-27T07:49:44Z

Shouldn't the SAFETY comments in grow_amortized() and grow_exact() be also updated? They say that "finish_grow would have resulted in a capacity overflow if we tried to allocate more than isize::MAX items" while in fact this is due to the call of layout_array() in both cases.

btj · 2025-08-27T09:13:54Z

You're right. Updated.

tgross35 · 2025-09-03T00:03:00Z

The limits should stay via Layout but just in case,

@bors2 try @rust-timer queue

Could you also squash please? r=me after that, assuming perf doesn't have anything weird.

raw_vec.rs: Remove superfluous fn alloc_guard

rust-bors · 2025-09-03T02:18:24Z

☀️ Try build successful (CI)
Build commit: dacfb46 (dacfb46383aa2dc3ddd1589aa5c170ef9de84542, parent: 51ff895062ba60a7cba53f57af928c3fb7b0f2f4)

rust-timer · 2025-09-03T03:28:34Z

Finished benchmarking commit (dacfb46): comparison URL.

Overall result: ✅ improvements - no action needed

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.

@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)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-0.1%	[-0.1%, -0.1%]	1
All ❌✅ (primary)	-	-	0

Max RSS (memory usage)

Results (primary -4.4%)

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)	-	-	0
Improvements ✅ (primary)	-4.4%	[-4.4%, -4.4%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-4.4%	[-4.4%, -4.4%]	1

Cycles

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

Binary size

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Bootstrap: 465.874s -> 463.341s (-0.54%)
Artifact size: 388.34 MiB -> 388.26 MiB (-0.02%)

It checks that its argument is at most isize::MAX, but it is called only with layout sizes, which are already guaranteed to be at most isize::MAX.

btj · 2025-09-03T05:36:42Z

r? tgross35

tgross35 · 2025-09-03T05:49:15Z

Thank you!
@bors r+ rollup

bors · 2025-09-03T05:49:18Z

📌 Commit d9dc20c has been approved by tgross35

It is now in the queue for this repository.

raw_vec.rs: Remove superfluous fn alloc_guard `alloc_guard` checks that its argument is at most `isize::MAX`, but it is called only with layout sizes, which are already guaranteed to be at most `isize::MAX`.

Rollup of 9 pull requests Successful merges: - #143725 (core: add Peekable::next_if_map) - #145209 (Stabilize `path_add_extension`) - #145750 (raw_vec.rs: Remove superfluous fn alloc_guard) - #145962 (Ensure we emit an allocator shim when only some crate types need one) - #145963 (Add LSX accelerated implementation for source file analysis) - #146054 (add `#[must_use]` to `array::repeat`) - #146090 (Derive `PartialEq` for `InvisibleOrigin`) - #146120 (Correct typo in `rustc_errors` comment) - #146131 (rustdoc-search: add test case for indexing every item type) r? `@ghost` `@rustbot` modify labels: rollup

raw_vec.rs: Remove superfluous fn alloc_guard `alloc_guard` checks that its argument is at most `isize::MAX`, but it is called only with layout sizes, which are already guaranteed to be at most `isize::MAX`.

Rollup of 15 pull requests Successful merges: - #143725 (core: add Peekable::next_if_map) - #145209 (Stabilize `path_add_extension`) - #145750 (raw_vec.rs: Remove superfluous fn alloc_guard) - #145962 (Ensure we emit an allocator shim when only some crate types need one) - #145963 (Add LSX accelerated implementation for source file analysis) - #146054 (add `#[must_use]` to `array::repeat`) - #146090 (Derive `PartialEq` for `InvisibleOrigin`) - #146120 (Correct typo in `rustc_errors` comment) - #146127 (Rename `ToolRustc` to `ToolRustcPrivate`) - #146131 (rustdoc-search: add test case for indexing every item type) - #146133 (Revert "Make `lto` and `linker-plugin-lto` work the same for `compiler_builtins`) - #146134 (llvm: nvptx: Layout update to match LLVM) - #146136 (docs(std): add missing closing code block fences in doc comments) - #146137 (Disallow frontmatter in `--cfg` and `--check-cfg` arguments) - #146140 (compiletest: cygwin follows windows in using PATH for dynamic libraries) r? `@ghost` `@rustbot` modify labels: rollup

raw_vec.rs: Remove superfluous fn alloc_guard `alloc_guard` checks that its argument is at most `isize::MAX`, but it is called only with layout sizes, which are already guaranteed to be at most `isize::MAX`.

Rollup of 16 pull requests Successful merges: - #143725 (core: add Peekable::next_if_map) - #145209 (Stabilize `path_add_extension`) - #145342 (fix drop scope for `super let` bindings within `if let`) - #145750 (raw_vec.rs: Remove superfluous fn alloc_guard) - #145962 (Ensure we emit an allocator shim when only some crate types need one) - #145963 (Add LSX accelerated implementation for source file analysis) - #146054 (add `#[must_use]` to `array::repeat`) - #146090 (Derive `PartialEq` for `InvisibleOrigin`) - #146120 (Correct typo in `rustc_errors` comment) - #146127 (Rename `ToolRustc` to `ToolRustcPrivate`) - #146133 (Revert "Make `lto` and `linker-plugin-lto` work the same for `compiler_builtins`) - #146134 (llvm: nvptx: Layout update to match LLVM) - #146136 (docs(std): add missing closing code block fences in doc comments) - #146137 (Disallow frontmatter in `--cfg` and `--check-cfg` arguments) - #146140 (compiletest: cygwin follows windows in using PATH for dynamic libraries) - #146156 (miri subtree update) r? `@ghost` `@rustbot` modify labels: rollup

raw_vec.rs: Remove superfluous fn alloc_guard `alloc_guard` checks that its argument is at most `isize::MAX`, but it is called only with layout sizes, which are already guaranteed to be at most `isize::MAX`.

Rollup of 24 pull requests Successful merges: - #140459 (Add `read_buf` equivalents for positioned reads) - #143725 (core: add Peekable::next_if_map) - #145209 (Stabilize `path_add_extension`) - #145342 (fix drop scope for `super let` bindings within `if let`) - #145750 (raw_vec.rs: Remove superfluous fn alloc_guard) - #145827 (On unused binding or binding not present in all patterns, suggest potential typo of unit struct/variant or const) - #145932 (Allow `inline(always)` with a target feature behind a unstable feature `target_feature_inline_always`.) - #145962 (Ensure we emit an allocator shim when only some crate types need one) - #145963 (Add LSX accelerated implementation for source file analysis) - #146054 (add `#[must_use]` to `array::repeat`) - #146090 (Derive `PartialEq` for `InvisibleOrigin`) - #146112 (don't uppercase error messages) - #146120 (Correct typo in `rustc_errors` comment) - #146124 (Test `rustc-dev` in `distcheck`) - #146127 (Rename `ToolRustc` to `ToolRustcPrivate`) - #146131 (rustdoc-search: add test case for indexing every item type) - #146134 (llvm: nvptx: Layout update to match LLVM) - #146136 (docs(std): add missing closing code block fences in doc comments) - #146137 (Disallow frontmatter in `--cfg` and `--check-cfg` arguments) - #146140 (compiletest: cygwin follows windows in using PATH for dynamic libraries) - #146150 (fix(rustdoc): match rustc `--emit` precedence ) - #146155 (Make bootstrap self test parallel) - #146161 ([rustdoc] Uncomment code to add scraped rustdoc examples in loaded paths) - #146172 (triagebot: configure some pings when certain attributes are used) r? `@ghost` `@rustbot` modify labels: rollup

Rollup merge of #145750 - btj:drop-alloc-guard, r=tgross35 raw_vec.rs: Remove superfluous fn alloc_guard `alloc_guard` checks that its argument is at most `isize::MAX`, but it is called only with layout sizes, which are already guaranteed to be at most `isize::MAX`.

Rollup of 24 pull requests Successful merges: - rust-lang/rust#140459 (Add `read_buf` equivalents for positioned reads) - rust-lang/rust#143725 (core: add Peekable::next_if_map) - rust-lang/rust#145209 (Stabilize `path_add_extension`) - rust-lang/rust#145342 (fix drop scope for `super let` bindings within `if let`) - rust-lang/rust#145750 (raw_vec.rs: Remove superfluous fn alloc_guard) - rust-lang/rust#145827 (On unused binding or binding not present in all patterns, suggest potential typo of unit struct/variant or const) - rust-lang/rust#145932 (Allow `inline(always)` with a target feature behind a unstable feature `target_feature_inline_always`.) - rust-lang/rust#145962 (Ensure we emit an allocator shim when only some crate types need one) - rust-lang/rust#145963 (Add LSX accelerated implementation for source file analysis) - rust-lang/rust#146054 (add `#[must_use]` to `array::repeat`) - rust-lang/rust#146090 (Derive `PartialEq` for `InvisibleOrigin`) - rust-lang/rust#146112 (don't uppercase error messages) - rust-lang/rust#146120 (Correct typo in `rustc_errors` comment) - rust-lang/rust#146124 (Test `rustc-dev` in `distcheck`) - rust-lang/rust#146127 (Rename `ToolRustc` to `ToolRustcPrivate`) - rust-lang/rust#146131 (rustdoc-search: add test case for indexing every item type) - rust-lang/rust#146134 (llvm: nvptx: Layout update to match LLVM) - rust-lang/rust#146136 (docs(std): add missing closing code block fences in doc comments) - rust-lang/rust#146137 (Disallow frontmatter in `--cfg` and `--check-cfg` arguments) - rust-lang/rust#146140 (compiletest: cygwin follows windows in using PATH for dynamic libraries) - rust-lang/rust#146150 (fix(rustdoc): match rustc `--emit` precedence ) - rust-lang/rust#146155 (Make bootstrap self test parallel) - rust-lang/rust#146161 ([rustdoc] Uncomment code to add scraped rustdoc examples in loaded paths) - rust-lang/rust#146172 (triagebot: configure some pings when certain attributes are used) r? `@ghost` `@rustbot` modify labels: rollup

rustbot added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. T-libs Relevant to the library team, which will review and decide on the PR/issue. labels Aug 22, 2025

btj marked this pull request as ready for review August 22, 2025 18:16

rustbot assigned thomcc Aug 22, 2025

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Aug 22, 2025

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rust-bors bot added a commit that referenced this pull request Sep 3, 2025

Auto merge of #145750 - btj:drop-alloc-guard, r=<try>

dacfb46

raw_vec.rs: Remove superfluous fn alloc_guard

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rustbot removed the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Sep 3, 2025

raw_vec.rs: Remove superfluous fn alloc_guard

d9dc20c

It checks that its argument is at most isize::MAX, but it is called only with layout sizes, which are already guaranteed to be at most isize::MAX.

btj force-pushed the drop-alloc-guard branch from d185b06 to d9dc20c Compare September 3, 2025 05:35

rustbot assigned tgross35 and unassigned thomcc Sep 3, 2025

tgross35 approved these changes Sep 3, 2025

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bors removed the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Sep 3, 2025

bors added the S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. label Sep 3, 2025

tgross35 mentioned this pull request Sep 3, 2025

Rollup of 9 pull requests #146147

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jhpratt mentioned this pull request Sep 3, 2025

Rollup of 15 pull requests #146153

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Zalathar mentioned this pull request Sep 3, 2025

Rollup of 16 pull requests #146158

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Zalathar mentioned this pull request Sep 4, 2025

Rollup of 24 pull requests #146185

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bors merged commit d71a9b6 into rust-lang:master Sep 4, 2025
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Overall result: ✅ improvements - no action needed

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