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

cjgillot · 2025-10-16T22:24:36Z

Fixes #119729
Keeps #136175 as it involves offset_of! which this PR does not touch.

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

rustbot · 2025-10-21T00:37:59Z

oli-obk is not on the review rotation at the moment.
They may take a while to respond.

compiler/rustc_codegen_cranelift/example/mini_core.rs

scottmcm · 2025-10-21T18:04:26Z

compiler/rustc_codegen_ssa/src/mir/rvalue.rs

                let ty = self.monomorphize(ty);
                let layout = bx.cx().layout_of(ty);
                let val = match null_op {
-                    mir::NullOp::SizeOf => {


(No action) I do like that this means the different backends don't need this any more, which is nice since it all needs to match what CTFE did anyway 👍

scottmcm · 2025-10-21T18:09:16Z

tests/mir-opt/box_expr.main.ElaborateDrops.diff

-          _2 = SizeOf(S);
-          _3 = AlignOf(S);
-          _4 = alloc::alloc::exchange_malloc(move _2, move _3) -> [return: bb1, unwind continue];
+          _2 = alloc::alloc::exchange_malloc(const <S as std::mem::SizedTypeProperties>::SIZE, const <S as std::mem::SizedTypeProperties>::ALIGN) -> [return: bb1, unwind continue];


Lovely to see this inline and no longer need the locals 👍

scottmcm · 2025-10-21T18:15:20Z

tests/mir-opt/const_prop/boxes.main.GVN.panic-abort.diff

-+         _4 = const 4_usize;
-+         _5 = const 4_usize;
-+         _6 = alloc::alloc::exchange_malloc(const 4_usize, const 4_usize) -> [return: bb1, unwind unreachable];
+          _4 = alloc::alloc::exchange_malloc(const <i32 as std::mem::SizedTypeProperties>::SIZE, const <i32 as std::mem::SizedTypeProperties>::ALIGN) -> [return: bb1, unwind unreachable];


Just confirming: the reason this is still the const, rather than 4_usize is that this is a GVN unit test? Some other pass is going to evaluate it in the normal flow, right?

Or does it not matter because anything asking for try_eval_target_usize on the const will get the value either way?

Oh, that's because GVN avoids to evaluate constants in-place. That does not really matter, any code that needs to evaluate it will easily. If we need it, it's a 3-line change in GVN, but I'd rather do it in a separate PR.

I definitely don't think it's GVN's problem. If it's useful to do, I'd probably do it in InstSimplify or something, since it could be done locally. Agreed no need for it in this PR.

And TBH I don't know how important it is. I did a bit more digging, and it looks like try_eval_target_usize will end up in const_eval_resolve+const_eval_global_id, so probably anyone looking at the constant will get the value they need anyway, so might not be worth bothering.

(I don't know if there are paths that only look at Const::Val and skip Const::Unevaluated, though. I guess we can always worry about that later if needed.)

So I think this can be "won't fix"ed.

compiler/rustc_mir_transform/src/check_alignment.rs

scottmcm · 2025-10-21T18:35:26Z

compiler/rustc_public/src/mir/body.rs

-    /// Returns the size of a value of that type.
-    SizeOf,
-    /// Returns the minimum alignment of a type.
-    AlignOf,


FYI @celinval

scottmcm

I left some comments along the way, but this looks good to me. r=me with minor updates to address things if you see fit. (Or wait for oli if you think this should go through someone more knowledgeable about const stuff.)

View changes since this review

bors · 2025-10-22T14:41:19Z

☔ The latest upstream changes (presumably #147687) made this pull request unmergeable. Please resolve the merge conflicts.

rustbot · 2025-10-23T00:33:39Z

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 · 2025-10-23T02:14:39Z

@bors r=scottmcm,oli-obk

bors · 2025-10-23T02:14:43Z

📌 Commit 5dfbf67 has been approved by scottmcm,oli-obk

It is now in the queue for this repository.

bors · 2025-10-23T05:09:28Z

⌛ Testing commit 5dfbf67 with merge 4b3ba58...

bors · 2025-10-23T08:15:56Z

☀️ Test successful - checks-actions
Approved by: scottmcm,oli-obk
Pushing 4b3ba58 to master...

github-actions · 2025-10-23T08:19:44Z

What is this?

This is an experimental post-merge analysis report that shows differences in test outcomes between the merged PR and its parent PR.

Comparing 7838ce1 (parent) -> 4b3ba58 (this PR)

Test differences

Show 52 test diffs

Stage 1

[crashes] tests/crashes/114663.rs: pass -> [missing] (J1)
[crashes] tests/crashes/119729.rs: pass -> [missing] (J1)
[crashes] tests/crashes/136175.rs: pass -> [missing] (J1)
[ui] tests/ui/const-generics/generic_const_exprs/size_of-dyn-trait-2.rs: [missing] -> pass (J1)
[ui] tests/ui/const-generics/generic_const_exprs/size_of-dyn-trait-3.rs: [missing] -> pass (J1)
[ui] tests/ui/const-generics/generic_const_exprs/size_of-dyn-trait.rs: [missing] -> pass (J1)

Stage 2

[crashes] tests/crashes/114663.rs: pass -> [missing] (J0)
[crashes] tests/crashes/119729.rs: pass -> [missing] (J0)
[crashes] tests/crashes/136175.rs: pass -> [missing] (J0)
[ui] tests/ui/const-generics/generic_const_exprs/size_of-dyn-trait-2.rs: [missing] -> pass (J2)
[ui] tests/ui/const-generics/generic_const_exprs/size_of-dyn-trait-3.rs: [missing] -> pass (J2)
[ui] tests/ui/const-generics/generic_const_exprs/size_of-dyn-trait.rs: [missing] -> pass (J2)

Additionally, 40 doctest diffs were found. These are ignored, as they are noisy.

Job group index

Test dashboard

Run

cargo run --manifest-path src/ci/citool/Cargo.toml -- \
    test-dashboard 4b3ba5844e8831c9b3ee5a5643cdff5da0677426 --output-dir test-dashboard

And then open test-dashboard/index.html in your browser to see an overview of all executed tests.

Job duration changes

aarch64-apple: 8512.0s -> 6923.8s (-18.7%)
x86_64-gnu-llvm-20: 2404.1s -> 2842.5s (18.2%)
dist-x86_64-apple: 7185.0s -> 6096.5s (-15.2%)
dist-aarch64-apple: 6702.2s -> 5767.2s (-14.0%)
dist-various-2: 2223.4s -> 1967.1s (-11.5%)
armhf-gnu: 4926.0s -> 5489.8s (11.4%)
dist-armhf-linux: 4864.6s -> 5321.3s (9.4%)
x86_64-gnu-llvm-20-1: 3236.2s -> 3521.1s (8.8%)
x86_64-gnu-gcc: 3136.2s -> 3411.5s (8.8%)
arm-android: 5820.1s -> 6227.1s (7.0%)

How to interpret the job duration changes?

Job durations can vary a lot, based on the actual runner instance
that executed the job, system noise, invalidated caches, etc. The table above is provided
mostly for t-infra members, for simpler debugging of potential CI slow-downs.

rust-timer · 2025-10-23T09:26:30Z

Finished benchmarking commit (4b3ba58): comparison URL.

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

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%, 0.5%]	3
Regressions ❌ (secondary)	0.3%	[0.1%, 0.7%]	30
Improvements ✅ (primary)	-0.4%	[-0.7%, -0.1%]	4
Improvements ✅ (secondary)	-0.3%	[-0.7%, -0.1%]	5
All ❌✅ (primary)	-0.1%	[-0.7%, 0.5%]	7

Max RSS (memory usage)

Results (primary -0.1%, secondary 1.9%)

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

	mean	range	count
Regressions ❌ (primary)	2.2%	[0.5%, 4.8%]	5
Regressions ❌ (secondary)	3.5%	[0.6%, 6.3%]	18
Improvements ✅ (primary)	-2.3%	[-4.3%, -1.2%]	5
Improvements ✅ (secondary)	-1.8%	[-3.0%, -0.8%]	8
All ❌✅ (primary)	-0.1%	[-4.3%, 4.8%]	10

Cycles

Results (primary 1.3%, secondary -1.5%)

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

	mean	range	count
Regressions ❌ (primary)	1.3%	[1.3%, 1.3%]	1
Regressions ❌ (secondary)	5.3%	[1.7%, 9.2%]	7
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-4.6%	[-13.1%, -2.0%]	15
All ❌✅ (primary)	1.3%	[1.3%, 1.3%]	1

Binary size

Results (primary -0.0%, secondary -0.1%)

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%]	21
Regressions ❌ (secondary)	0.0%	[0.0%, 0.1%]	11
Improvements ✅ (primary)	-0.1%	[-0.8%, -0.0%]	19
Improvements ✅ (secondary)	-0.6%	[-0.8%, -0.3%]	3
All ❌✅ (primary)	-0.0%	[-0.8%, 0.4%]	40

Bootstrap: 473.667s -> 474.933s (0.27%)
Artifact size: 390.66 MiB -> 390.48 MiB (-0.05%)

Relevant upstream PR: - rust-lang/rust#147793 (Replace NullOp::SizeOf and NullOp::AlignOf by lang items.) Resolves: model-checking#4425

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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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cjgillot force-pushed the no-null-op branch from 001f9d2 to 95ec7ab Compare October 23, 2025 00:33

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

5dfbf67

cjgillot force-pushed the no-null-op branch from 95ec7ab to 5dfbf67 Compare October 23, 2025 00:38

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 Oct 23, 2025

bors added the merged-by-bors This PR was explicitly merged by bors. label Oct 23, 2025

bors merged commit 4b3ba58 into rust-lang:master Oct 23, 2025
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rustbot added this to the 1.92.0 milestone Oct 23, 2025

bors mentioned this pull request Oct 23, 2025

[EXPERIMENT] Introduce TypingMode::Codegen to avoid layout cycles #145477

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bors mentioned this pull request Oct 23, 2025

Remove box_new intrinsic #147862

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cjgillot deleted the no-null-op branch October 23, 2025 10:12

tautschnig added a commit to tautschnig/kani that referenced this pull request Oct 24, 2025

Upgrade Rust toolchain to 2025-10-24

d0592d0

Relevant upstream PR: - rust-lang/rust#147793 (Replace NullOp::SizeOf and NullOp::AlignOf by lang items.) Resolves: model-checking#4425

tautschnig mentioned this pull request Oct 24, 2025

Upgrade Rust toolchain to 2025-10-24 model-checking/kani#4426

Open

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

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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Test differences

Stage 1

Stage 2

Job duration changes

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

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