const-eval: fix and re-enable pointer fragment support #148259

RalfJung · 2025-10-29T17:00:42Z

The pointer fragment support from #144081 got disabled due to #146291. This brings it back. To fix the issue, the per-byte provenance fragment tracking tracks both the provenance and raw address of the full pointer, so we can ensure that only fragments that are truly part of the same pointer are being merged.

r? @oli-obk
Cc @theemathas
Fixes rust-lang/const-eval#72 again.
Also fixes #147959.

@traviscross I assume this won't need another t-lang FCP since it already got FCP'd in #144081?

rustbot · 2025-10-29T17:00:45Z

Some changes occurred to the CTFE / Miri interpreter

cc @rust-lang/miri

Some changes occurred to the CTFE / Miri interpreter

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

Some changes occurred to the CTFE machinery

cc @RalfJung, @oli-obk, @lcnr

The Miri subtree was changed

cc @rust-lang/miri

rustbot · 2025-10-29T17:00:48Z

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

traviscross · 2025-10-29T19:17:54Z

I assume this won't need another t-lang FCP since it already got FCP'd in #144081?

As I commented a moment ago on an unrelated matter in #145954 (comment):

As a procedural matter, though the FCP in ... did originally cover what's here, the fact that it was merged without that puts the ball back in our court, in the same way that if one of our stabilizations is reverted, we then need to re-FCP the restabilization. In this way, our FCPs represent a "point-in-time" decision to stabilize something.

We discussed that procedural analysis in the meeting and it seemed right to people.

In that light, we would FCP the restabilization here. It should be an easy call for us given the earlier decision.

traviscross · 2025-10-29T19:21:17Z

This seems right to me. I propose we restabilize this.

@rfcbot fcp merge

rust-rfcbot · 2025-10-29T19:21:19Z

Team member @traviscross has proposed to merge this. The next step is review by the rest of the tagged team members:

No concerns currently listed.

Once a majority of reviewers approve (and at most 2 approvals are outstanding), this will enter its final comment period. If you spot a major issue that hasn't been raised at any point in this process, please speak up!

cc @rust-lang/lang-advisors: FCP proposed for lang, please feel free to register concerns.
See this document for info about what commands tagged team members can give me.

compiler/rustc_middle/src/mir/interpret/allocation/provenance_map.rs

RalfJung · 2025-10-29T19:41:01Z

compiler/rustc_middle/src/mir/interpret/pointer.rs

    fn get_alloc_id(self) -> Option<AllocId>;
-
-    /// Defines the 'join' of provenance: what happens when doing a pointer load and different bytes have different provenance.
-    fn join(left: Self, right: Self) -> Option<Self>;


I'm getting rid of the join function because the code that used it anyway had to special-case wildcards, and then it became easier to just have the entire wildcard logic there rather than having some of it inside join.

compiler/rustc_const_eval/src/interpret/memory.rs

theemathas · 2025-10-30T01:41:27Z

Do we need tests for #147959?

RalfJung · 2025-10-30T07:02:20Z

Do we need tests for #147959?

Good point, I added that.

oli-obk

r=me with FCP finished

View changes since this review

RalfJung · 2025-11-08T13:44:24Z

@oli-obk I have added a commit to reduce the impact of #148470, so this needs another review I am afraid.

RalfJung · 2025-11-08T13:46:09Z

@bors try
@rust-timer queue

const-eval: fix and re-enable pointer fragment support

rust-bors · 2025-11-08T15:59:07Z

☀️ Try build successful (CI)
Build commit: 4c5660e (4c5660ea2a32ea020121eb500fe05792d673a4d4, parent: bbb6f68e2888eea989337d558b47372ecf110e08)

rust-timer · 2025-11-08T18:10:55Z

Finished benchmarking commit (4c5660e): comparison URL.

Overall result: ❌ regressions - 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)	0.1%	[0.1%, 0.1%]	1
Regressions ❌ (secondary)	1.2%	[0.8%, 1.6%]	10
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.1%	[0.1%, 0.1%]	1

Max RSS (memory usage)

Results (secondary 3.2%)

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)	3.2%	[2.2%, 4.3%]	2
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Cycles

Results (secondary -2.3%)

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)	2.3%	[2.3%, 2.3%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-3.4%	[-4.8%, -2.1%]	4
All ❌✅ (primary)	-	-	0

Binary size

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

Bootstrap: 474.693s -> 477.255s (0.54%)
Artifact size: 390.92 MiB -> 391.03 MiB (0.03%)

RalfJung · 2025-11-09T09:39:27Z

@bors try
@rust-timer queue

const-eval: fix and re-enable pointer fragment support

rust-bors · 2025-11-09T11:53:20Z

☀️ Try build successful (CI)
Build commit: 2b58ae9 (2b58ae9fcb18e5e96469f20532bc824b8af6dfac, parent: acda5e9f9aadac705b851935b14aa3d34a67d428)

rust-timer · 2025-11-09T14:23:55Z

Finished benchmarking commit (2b58ae9): comparison URL.

Overall result: ❌ regressions - 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)	0.0%	[0.0%, 0.0%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Max RSS (memory usage)

Results (primary 0.6%)

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

	mean	range	count
Regressions ❌ (primary)	0.6%	[0.6%, 0.6%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.6%	[0.6%, 0.6%]	1

Cycles

Results (secondary -3.4%)

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)	-	-	0
Improvements ✅ (secondary)	-3.4%	[-3.4%, -3.4%]	1
All ❌✅ (primary)	-	-	0

Binary size

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

Bootstrap: 474.157s -> 476.71s (0.54%)
Artifact size: 390.96 MiB -> 391.05 MiB (0.02%)

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. T-libs Relevant to the library team, which will review and decide on the PR/issue. labels Oct 29, 2025

rustbot assigned oli-obk Oct 29, 2025

RalfJung force-pushed the const-ptr-fragment branch from 9058e28 to 4cce5fe Compare October 29, 2025 17:40

RalfJung added I-lang-nominated Nominated for discussion during a lang team meeting. I-lang-easy-decision Issue: The decision needed by the team is conjectured to be easy; this does not imply nomination labels Oct 29, 2025

rust-rfcbot added proposed-final-comment-period Proposed to merge/close by relevant subteam, see T-<team> label. Will enter FCP once signed off. disposition-merge This issue / PR is in PFCP or FCP with a disposition to merge it. labels Oct 29, 2025

traviscross added the T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. label Oct 29, 2025

RalfJung commented Oct 29, 2025

View reviewed changes

compiler/rustc_middle/src/mir/interpret/allocation/provenance_map.rs Outdated Show resolved Hide resolved

RalfJung force-pushed the const-ptr-fragment branch 2 times, most recently from 4e023d0 to 739d035 Compare October 29, 2025 19:38

RalfJung commented Oct 29, 2025

View reviewed changes

RalfJung force-pushed the const-ptr-fragment branch from 739d035 to 32b18d6 Compare October 29, 2025 19:45

theemathas reviewed Oct 30, 2025

View reviewed changes

compiler/rustc_const_eval/src/interpret/memory.rs Outdated Show resolved Hide resolved

RalfJung force-pushed the const-ptr-fragment branch from 32b18d6 to bfad332 Compare October 30, 2025 07:04

oli-obk approved these changes Nov 5, 2025

View reviewed changes

const-eval: fix and re-enable pointer fragment support

42455aa

RalfJung force-pushed the const-ptr-fragment branch from 07d1835 to 42455aa Compare November 5, 2025 21:12

RalfJung added the S-waiting-on-fcp Status: PR is in FCP and is awaiting for FCP to complete. label Nov 8, 2025

This comment has been minimized.

Sign in to view

rust-bors bot added a commit that referenced this pull request Nov 8, 2025

Auto merge of #148259 - RalfJung:const-ptr-fragment, r=<try>

4c5660e

const-eval: fix and re-enable pointer fragment support

rustbot added the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Nov 8, 2025

This comment has been minimized.

Sign in to view

rustbot added perf-regression Performance regression. and removed S-waiting-on-perf Status: Waiting on a perf run to be completed. labels Nov 8, 2025

when writing a scalar pair, always reset the entire destination range

5d5d229

RalfJung force-pushed the const-ptr-fragment branch from 7ad9038 to 5d5d229 Compare November 9, 2025 09:38

This comment has been minimized.

Sign in to view

rust-bors bot added a commit that referenced this pull request Nov 9, 2025

Auto merge of #148259 - RalfJung:const-ptr-fragment, r=<try>

2b58ae9

const-eval: fix and re-enable pointer fragment support

rustbot added the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Nov 9, 2025

This comment has been minimized.

Sign in to view

rustbot removed perf-regression Performance regression. S-waiting-on-perf Status: Waiting on a perf run to be completed. labels Nov 9, 2025

const-eval: fix and re-enable pointer fragment support #148259

Are you sure you want to change the base?

const-eval: fix and re-enable pointer fragment support #148259

Conversation

RalfJung commented Oct 29, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

rustbot commented Oct 29, 2025

Uh oh!

rustbot commented Oct 29, 2025

Uh oh!

traviscross commented Oct 29, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

traviscross commented Oct 29, 2025

Uh oh!

rust-rfcbot commented Oct 29, 2025 • edited by scottmcm Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Uh oh!

theemathas commented Oct 30, 2025

Uh oh!

RalfJung commented Oct 30, 2025

Uh oh!

oli-obk left a comment • edited by rustbot Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Choose a reason for hiding this comment

Uh oh!

RalfJung commented Nov 8, 2025

Uh oh!

RalfJung commented Nov 8, 2025

Uh oh!

This comment has been minimized.

This comment has been minimized.

rust-bors bot commented Nov 8, 2025

Uh oh!

This comment has been minimized.

rust-timer commented Nov 8, 2025

Overall result: ❌ regressions - please read the text below

Uh oh!

RalfJung commented Nov 9, 2025

Uh oh!

This comment has been minimized.

This comment has been minimized.

rust-bors bot commented Nov 9, 2025

Uh oh!

This comment has been minimized.

rust-timer commented Nov 9, 2025

Overall result: ❌ regressions - no action needed

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

9 participants

RalfJung commented Oct 29, 2025 •

edited

Loading

traviscross commented Oct 29, 2025 •

edited

Loading

rust-rfcbot commented Oct 29, 2025 •

edited by scottmcm

Loading

oli-obk left a comment •

edited by rustbot

Loading