Don't emit two `assume`s in transmutes when one is a subset of the other #144209

scottmcm · 2025-07-20T07:19:39Z

For example, transmuting between bool and Ordering doesn't need two assumes because one range is a superset of the other.

Multiple are still used for things like char <-> NonZero<u32>, which overlap but where neither fully contains the other.

rustbot · 2025-07-20T07:19:43Z

r? @lcnr

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rustbot · 2025-07-20T07:19:45Z

Some changes occurred in compiler/rustc_codegen_ssa

cc @WaffleLapkin

oli-obk · 2025-07-20T12:01:27Z

@bors2 try @rust-timer queue

rust-bors · 2025-07-20T12:01:31Z

⌛ Trying commit dd170e8 with merge 4e27cc3…

To cancel the try build, run the command @bors2 try cancel.

Don't emit two `assume`s in transmutes when one is a subset of the other For example, transmuting between `bool` and `Ordering` doesn't need two `assume`s because one range is a superset of the other. Multiple are still used for things like `char` <-> `NonZero<u32>`, which overlap but where neither fully contains the other.

rust-bors · 2025-07-20T14:15:29Z

☀️ Try build successful (CI)
Build commit: 4e27cc3 (4e27cc328172a524edb4dd605053867dc92cddfa, parent: 81af9d45698a19183b8552079cbc7bf893fad1e5)

rust-timer · 2025-07-20T15:27:45Z

Finished benchmarking commit (4e27cc3): comparison URL.

Overall result: no relevant changes - 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

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

Max RSS (memory usage)

Results (primary -2.9%, secondary 4.6%)

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)	4.6%	[4.6%, 4.6%]	1
Improvements ✅ (primary)	-2.9%	[-3.1%, -2.7%]	2
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-2.9%	[-3.1%, -2.7%]	2

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: 465.3s -> 465.355s (0.01%)
Artifact size: 374.58 MiB -> 374.59 MiB (0.00%)

lcnr

r=me

I haven't looked at the test annotations in detail and don't feel 100% comfortable approving these. The code changes make sense the tests seem about right from what I can tell 😅 😁

scottmcm · 2025-07-21T21:43:07Z

@dianqk Perhaps you could double-check that the test updates here seem reasonable to you?

(This PR is not urgent; don't feel pressured to get to it promptly.)

bors · 2025-07-22T23:07:12Z

☔ The latest upstream changes (presumably #144249) made this pull request unmergeable. Please resolve the merge conflicts.

dianqk

r=me also after a nit.

(This PR is not urgent; don't feel pressured to get to it promptly.)

Never mind, I never felt that. I was just giving an estimated time.

compiler/rustc_abi/src/lib.rs

For example, transmuting between `bool` and `Ordering` doesn't need two `assume`s because one range is a superset of the other. Multiple are still used for things like `char` <-> `NonZero<u32>`, which overlap but where neither fully contains the other.

scottmcm · 2025-07-23T18:23:39Z

@bors r=lcnr,dianqk rollup=maybe (no perf changes in the report, so don't think it needs the separate run)

bors · 2025-07-23T18:23:42Z

📌 Commit a93a9aa has been approved by lcnr,dianqk

It is now in the queue for this repository.

Don't emit two `assume`s in transmutes when one is a subset of the other For example, transmuting between `bool` and `Ordering` doesn't need two `assume`s because one range is a superset of the other. Multiple are still used for things like `char` <-> `NonZero<u32>`, which overlap but where neither fully contains the other.

Rollup of 16 pull requests Successful merges: - #142569 (Suggest clone in user-write-code instead of inside macro) - #143401 (tests: Don't check for self-printed output in std-backtrace.rs test) - #143424 (clippy fix: rely on autoderef) - #143970 (Update core::mem::copy documentation) - #143979 (Test fixes for Arm64EC Windows) - #144160 (tests: debuginfo: Work around or disable broken tests on powerpc) - #144200 (Tweak output for non-`Clone` values moved into closures) - #144209 (Don't emit two `assume`s in transmutes when one is a subset of the other) - #144225 (Don't special-case llvm.* as nounwind) - #144314 (Hint that choose_pivot returns index in bounds) - #144316 (bootstrap: Move musl-root fallback out of sanity check) - #144364 (Update `dlmalloc` dependency of libstd) - #144368 (resolve: Remove `Scope::CrateRoot`) - #144373 (remove deprecated Error::description in impls) - #144390 (Remove dead code and extend test coverage and diagnostics around it) - #144392 (rustc_public: Remove movability from `RigidTy/AggregateKind::Coroutine`) r? `@ghost` `@rustbot` modify labels: rollup

Don't emit two `assume`s in transmutes when one is a subset of the other For example, transmuting between `bool` and `Ordering` doesn't need two `assume`s because one range is a superset of the other. Multiple are still used for things like `char` <-> `NonZero<u32>`, which overlap but where neither fully contains the other.

Rollup of 17 pull requests Successful merges: - #142569 (Suggest clone in user-write-code instead of inside macro) - #143401 (tests: Don't check for self-printed output in std-backtrace.rs test) - #143424 (clippy fix: rely on autoderef) - #143970 (Update core::mem::copy documentation) - #143979 (Test fixes for Arm64EC Windows) - #144160 (tests: debuginfo: Work around or disable broken tests on powerpc) - #144200 (Tweak output for non-`Clone` values moved into closures) - #144209 (Don't emit two `assume`s in transmutes when one is a subset of the other) - #144225 (Don't special-case llvm.* as nounwind) - #144314 (Hint that choose_pivot returns index in bounds) - #144316 (bootstrap: Move musl-root fallback out of sanity check) - #144340 (UI test suite clarity changes: Rename `tests/ui/SUMMARY.md` and update rustc dev guide on `error-pattern`) - #144364 (Update `dlmalloc` dependency of libstd) - #144368 (resolve: Remove `Scope::CrateRoot`) - #144390 (Remove dead code and extend test coverage and diagnostics around it) - #144392 (rustc_public: Remove movability from `RigidTy/AggregateKind::Coroutine`) - #144424 (Allow setting `release-blog-post` label with rustbot) r? `@ghost` `@rustbot` modify labels: rollup

Don't emit two `assume`s in transmutes when one is a subset of the other For example, transmuting between `bool` and `Ordering` doesn't need two `assume`s because one range is a superset of the other. Multiple are still used for things like `char` <-> `NonZero<u32>`, which overlap but where neither fully contains the other.

Rollup of 16 pull requests Successful merges: - #142569 (Suggest clone in user-write-code instead of inside macro) - #143401 (tests: Don't check for self-printed output in std-backtrace.rs test) - #143424 (clippy fix: rely on autoderef) - #143970 (Update core::mem::copy documentation) - #143979 (Test fixes for Arm64EC Windows) - #144160 (tests: debuginfo: Work around or disable broken tests on powerpc) - #144200 (Tweak output for non-`Clone` values moved into closures) - #144209 (Don't emit two `assume`s in transmutes when one is a subset of the other) - #144314 (Hint that choose_pivot returns index in bounds) - #144316 (bootstrap: Move musl-root fallback out of sanity check) - #144340 (UI test suite clarity changes: Rename `tests/ui/SUMMARY.md` and update rustc dev guide on `error-pattern`) - #144364 (Update `dlmalloc` dependency of libstd) - #144368 (resolve: Remove `Scope::CrateRoot`) - #144390 (Remove dead code and extend test coverage and diagnostics around it) - #144392 (rustc_public: Remove movability from `RigidTy/AggregateKind::Coroutine`) - #144424 (Allow setting `release-blog-post` label with rustbot) r? `@ghost` `@rustbot` modify labels: rollup

Rollup of 12 pull requests Successful merges: - #142569 (Suggest clone in user-write-code instead of inside macro) - #143401 (tests: Don't check for self-printed output in std-backtrace.rs test) - #143424 (clippy fix: rely on autoderef) - #143970 (Update core::mem::copy documentation) - #143979 (Test fixes for Arm64EC Windows) - #144200 (Tweak output for non-`Clone` values moved into closures) - #144209 (Don't emit two `assume`s in transmutes when one is a subset of the other) - #144314 (Hint that choose_pivot returns index in bounds) - #144340 (UI test suite clarity changes: Rename `tests/ui/SUMMARY.md` and update rustc dev guide on `error-pattern`) - #144368 (resolve: Remove `Scope::CrateRoot`) - #144390 (Remove dead code and extend test coverage and diagnostics around it) - #144392 (rustc_public: Remove movability from `RigidTy/AggregateKind::Coroutine`) r? `@ghost` `@rustbot` modify labels: rollup

Rollup merge of #144209 - scottmcm:assume_less, r=lcnr,dianqk Don't emit two `assume`s in transmutes when one is a subset of the other For example, transmuting between `bool` and `Ordering` doesn't need two `assume`s because one range is a superset of the other. Multiple are still used for things like `char` <-> `NonZero<u32>`, which overlap but where neither fully contains the other.

rustbot assigned lcnr Jul 20, 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. labels Jul 20, 2025

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rustbot removed the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Jul 20, 2025

lcnr reviewed Jul 21, 2025

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dianqk self-assigned this Jul 22, 2025

dianqk approved these changes Jul 23, 2025

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compiler/rustc_abi/src/lib.rs Outdated Show resolved Hide resolved

scottmcm force-pushed the assume_less branch from dd170e8 to a93a9aa Compare July 23, 2025 16:16

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 Jul 23, 2025

fmease mentioned this pull request Jul 24, 2025

Rollup of 16 pull requests #144418

Closed

scottmcm mentioned this pull request Jul 24, 2025

Stop generating assumes for validity ranges #129027

Closed

fmease mentioned this pull request Jul 25, 2025

Rollup of 17 pull requests #144428

Closed

This was referenced Jul 25, 2025

Rollup of 16 pull requests #144436

Closed

Rollup of 12 pull requests #144440

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bors merged commit f414e7a into rust-lang:master Jul 25, 2025
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rustbot added this to the 1.90.0 milestone Jul 25, 2025

scottmcm deleted the assume_less branch July 25, 2025 16:22

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Don't emit two `assume`s in transmutes when one is a subset of the other #144209

Don't emit two `assume`s in transmutes when one is a subset of the other #144209

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Don't emit two assumes in transmutes when one is a subset of the other #144209

Don't emit two assumes in transmutes when one is a subset of the other #144209

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Overall result: no relevant changes - no action needed

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Don't emit two `assume`s in transmutes when one is a subset of the other #144209

Don't emit two `assume`s in transmutes when one is a subset of the other #144209