Replace NullOp::SizeOf and NullOp::AlignOf by lang items. #147793

cjgillot · 2025-10-16T22:24:36Z

cjgillot · 2025-10-16T22:33:04Z

Replace NullOp::SizeOf and NullOp::AlignOf by lang items.

rust-bors · 2025-10-17T00:45:10Z

☀️ Try build successful (CI)
Build commit: 2cefd8f (2cefd8ff4961f18771f6f840878942cbfbc03afe, parent: 53a741fc4b8cf2d8e7b1b2336ed8edf889db84f4)

rust-timer · 2025-10-17T01:54:54Z

Finished benchmarking commit (2cefd8f): 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)	0.5%	[0.4%, 0.6%]	3
Regressions ❌ (secondary)	0.7%	[0.5%, 0.7%]	4
Improvements ✅ (primary)	-0.2%	[-0.2%, -0.1%]	2
Improvements ✅ (secondary)	-0.2%	[-0.7%, -0.1%]	14
All ❌✅ (primary)	0.2%	[-0.2%, 0.6%]	5

Max RSS (memory usage)

Results (primary -0.3%, secondary -1.4%)

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

	mean	range	count
Regressions ❌ (primary)	1.5%	[0.4%, 3.0%]	8
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-3.4%	[-7.6%, -1.1%]	5
Improvements ✅ (secondary)	-1.4%	[-2.2%, -0.8%]	3
All ❌✅ (primary)	-0.3%	[-7.6%, 3.0%]	13

Cycles

Results (primary -2.9%, secondary 6.8%)

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)	6.8%	[6.8%, 6.8%]	1
Improvements ✅ (primary)	-2.9%	[-2.9%, -2.9%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-2.9%	[-2.9%, -2.9%]	1

Binary size

Results (primary -0.0%, secondary -0.3%)

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

	mean	range	count
Regressions ❌ (primary)	0.1%	[0.0%, 0.5%]	22
Regressions ❌ (secondary)	0.0%	[0.0%, 0.1%]	11
Improvements ✅ (primary)	-0.2%	[-0.8%, -0.0%]	18
Improvements ✅ (secondary)	-1.2%	[-3.2%, -0.3%]	4
All ❌✅ (primary)	-0.0%	[-0.8%, 0.5%]	40

Bootstrap: 475.105s -> 474.369s (-0.15%)
Artifact size: 390.35 MiB -> 390.39 MiB (0.01%)

library/core/src/mem/mod.rs

compiler/rustc_const_eval/src/interpret/intrinsics.rs

library/core/src/mem/mod.rs

bors · 2025-10-18T14:04:18Z

☔ The latest upstream changes (presumably #147654) made this pull request unmergeable. Please resolve the merge conflicts.

rustbot · 2025-10-19T18:05:01Z

This PR changes MIR

cc @oli-obk, @RalfJung, @JakobDegen, @vakaras

Some changes occurred to constck

cc @fee1-dead

Some changes occurred to the CTFE / Miri interpreter

cc @rust-lang/miri

Some changes occurred in compiler/rustc_codegen_ssa

cc @WaffleLapkin

Some changes occurred to the CTFE machinery

cc @RalfJung, @oli-obk, @lcnr

The Miri subtree was changed

cc @rust-lang/miri

This PR changes a file inside tests/crashes. If a crash was fixed, please move into the corresponding ui subdir and add 'Fixes #' to the PR description to autoclose the issue upon merge.

Some changes occurred in src/tools/clippy

cc @rust-lang/clippy

Some changes occurred in compiler/rustc_codegen_cranelift

cc @bjorn3

Some changes occurred to MIR optimizations

cc @rust-lang/wg-mir-opt

This PR changes rustc_public

cc @oli-obk, @celinval, @ouz-a

saethlin · 2025-10-19T19:16:39Z

The perf regressions are weird. I think they come from this:

rust/compiler/rustc_const_eval/src/const_eval/eval_queries.rs

Line 417 in c6efb90

let instance = with_no_trimmed_paths!(cid.instance.to_string());

where the interpreter is ??? pre-formatting errors ??

RalfJung · 2025-10-19T20:46:04Z

Hm yeah no idea why we are computing that string outside the closure...

rustbot · 2025-10-19T23:34:44Z

This PR was rebased onto a different master commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

cjgillot · 2025-10-19T23:51:08Z

@bors try @rust-timer queue

Replace NullOp::SizeOf and NullOp::AlignOf by lang items.

rust-bors · 2025-10-20T02:01:35Z

☀️ Try build successful (CI)
Build commit: ab65cea (ab65cead52dcf8e64ec14319f1c77892296050e5, parent: f04e3dfc87d7e2b6ad53e7a52253812cd62eba50)

rust-timer · 2025-10-20T03:56:06Z

Finished benchmarking commit (ab65cea): 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)	0.3%	[0.3%, 0.4%]	2
Regressions ❌ (secondary)	0.3%	[0.1%, 0.7%]	13
Improvements ✅ (primary)	-0.5%	[-1.0%, -0.2%]	4
Improvements ✅ (secondary)	-0.1%	[-0.3%, -0.0%]	5
All ❌✅ (primary)	-0.2%	[-1.0%, 0.4%]	6

Max RSS (memory usage)

Results (primary -1.3%, 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)	1.1%	[0.5%, 2.2%]	3
Regressions ❌ (secondary)	3.2%	[3.2%, 3.2%]	2
Improvements ✅ (primary)	-2.6%	[-4.7%, -1.5%]	6
Improvements ✅ (secondary)	-3.9%	[-5.7%, -1.3%]	12
All ❌✅ (primary)	-1.3%	[-4.7%, 2.2%]	9

Cycles

Results (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)	-	-	0
Regressions ❌ (secondary)	5.4%	[2.6%, 8.1%]	5
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-4.5%	[-6.9%, -3.0%]	3
All ❌✅ (primary)	-	-	0

Binary size

Results (primary -0.0%, secondary -0.4%)

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

	mean	range	count
Regressions ❌ (primary)	0.1%	[0.0%, 0.4%]	20
Regressions ❌ (secondary)	0.0%	[0.0%, 0.1%]	9
Improvements ✅ (primary)	-0.1%	[-0.8%, -0.0%]	19
Improvements ✅ (secondary)	-1.2%	[-3.1%, -0.3%]	4
All ❌✅ (primary)	-0.0%	[-0.8%, 0.4%]	39

Bootstrap: 473.871s -> 473.854s (-0.00%)
Artifact size: 388.68 MiB -> 388.39 MiB (-0.08%)

RalfJung · 2025-10-20T06:39:26Z

compiler/rustc_const_eval/src/const_eval/eval_queries.rs

    error: InterpErrorInfo<'tcx>,
 ) -> ErrorHandled {
    let (error, backtrace) = error.into_parts();
-    backtrace.print_backtrace();


This one here should stay -- it's part of how RUST_CTFE_BACKTRACE works. By default this is a fairly trivial NOP.

oli-obk · 2025-10-20T07:32:57Z

Instead of having the intrinsics const evaluated and requiring an actual body for the consts, we could also hijack const eval of these lang items directly and thus never have to do the work of actually evaluating their body.

RalfJung · 2025-10-20T08:32:49Z

I find the intrinsics route less confusing: - intrinsics for when the library needs to call into the compiler - lang items for when the compiler needs to call into the library However, if it makes a big enough perf difference, we could deviate from that pattern.

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cjgillot force-pushed the no-null-op branch from 5ca7d48 to b335a91 Compare October 16, 2025 22:32

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Auto merge of #147793 - cjgillot:no-null-op, r=<try>

2cefd8f

Replace NullOp::SizeOf and NullOp::AlignOf by lang items.

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rustbot added perf-regression Performance regression. and removed S-waiting-on-perf Status: Waiting on a perf run to be completed. labels Oct 17, 2025

cjgillot force-pushed the no-null-op branch from b335a91 to a785cc9 Compare October 17, 2025 01:57

rustbot added the T-clippy Relevant to the Clippy team. label Oct 17, 2025

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cjgillot force-pushed the no-null-op branch from 764278f to fa2dedc Compare October 19, 2025 16:02

cjgillot marked this pull request as ready for review October 19, 2025 18:04

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 Oct 19, 2025

cjgillot added 5 commits October 19, 2025 21:40

Replace NullOp::SizeOf and NullOp::AlignOf by lang items.

b3cbf7e

Update ui-fulldeps.

0d9544c

Bless miri.

9cf34ab

Adapt for 32bit.

35a6b51

Reduce work to report errors.

3d87bc1

cjgillot force-pushed the no-null-op branch from fa2dedc to 3d87bc1 Compare October 19, 2025 23:34

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rust-bors bot added a commit that referenced this pull request Oct 19, 2025

Auto merge of #147793 - cjgillot:no-null-op, r=<try>

ab65cea

Replace NullOp::SizeOf and NullOp::AlignOf by lang items.

rustbot added the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Oct 19, 2025

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

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Replace NullOp::SizeOf and NullOp::AlignOf by lang items. #147793

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Replace NullOp::SizeOf and NullOp::AlignOf by lang items. #147793

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

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

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