Stop useless caching of post-LTO artifact caching for fat LTO by bjorn3 · Pull Request #163317 · rust-lang/rust

bjorn3 · 2026-09-25T10:18:19Z

These artifacts are never actually used. Only the pre-LTO artifacts would be useful, but caching that seems a bit more tricky and is not that important for now. Fat LTO itself is very slow anyway.

Also move incr comp session dirs out of CodegenContext. CodegenContext will in the future be serialized and deserialized into a different rustc instance when -Zno-link/-Zlink-only is used. A separate incr comp session has to be used for both rustc invocations.

Part of rust-lang/compiler-team#908

rustbot · 2026-09-25T10:18:22Z

rustc_codegen_gcc is developed in its own repository. If possible, consider making this change to rust-lang/rustc_codegen_gcc instead.

cc @antoyo, @GuillaumeGomez

rustbot · 2026-09-25T10:18:25Z

r? @mejrs

rustbot has assigned @mejrs.
They will have a look at your PR within the next two weeks and either review your PR or reassign to another reviewer.

Use r? to explicitly pick a reviewer

Why was this reviewer chosen?

The reviewer was selected based on:

Owners of files modified in this PR: codegen, compiler
codegen, compiler expanded to 77 candidates
Random selection from 21 candidates

bjorn3 · 2026-09-25T12:12:09Z

            if !self.check_config(cfg) {
                debug!("check_attr: config does not match, ignoring attr");
-                return;
+                continue;


This caused us to skip all assertions after the first one with a cfg that doesn't match. Surprisingly nothing regressed by the lack of test coverage since the introduction of this bug.

View changes since the review

mejrs

Not sure about this otherwise.

r? @nnethercote perhaps?

View changes since this review

nnethercote

r=me with the nits addressed.

View changes since this review

nnethercote · 2026-10-02T03:03:32Z

+                };
+
+                // FIXME include pre-LTO bitcode in workproduct tracking
+                // FIXME add separate incr comp session for post-LTO outputs to use during link step


How important are these FIXMEs? Are you planning to fix them?

I'm working on a follow up PR to do this.

bjorn3 · 2026-10-02T09:01:09Z

@bors r=nnethercote

rust-bors · 2026-10-02T09:01:12Z

📌 Commit ebdd423 has been tentatively approved by nnethercote

It will be put into the queue for this repository once PR CI succeeds.

Fix incremental compilation for fat LTO Previously we would copy post-LTO artifacts into the incr comp cache for fat LTO despite them never getting used. Also the pre-LTO bitcode didn't get tracked and thus `determine_cgu_reuse` believed it had to regenerate bitcode for all CGUs even when all CGUs would be green. Also move incr comp session dirs out of `CodegenContext`. `CodegenContext` will in the future be serialized and deserialized into a different rustc instance when `-Zno-link`/`-Zlink-only` is used. A separate incr comp session has to be used for both rustc invocations. Part of rust-lang/compiler-team#908

…uwer Rollup of 13 pull requests Successful merges: - #163317 (Fix incremental compilation for fat LTO) - #163582 (Reapply "bootstrap: Enable rustdoc mergeable CCI for std and internal docs") - #151793 (Add mul_add_relaxed methods for floating-point types) - #162782 (Fix rustdoc ICE caused by mishandling of ambiguity errors) - #163010 (Miri can do dirfd now) - #163535 (Improve `DocStrings` perf) - #163576 (Fix `TypeOutlives` fast-path) - #163587 (Several small span improvements) - #163612 (fix `ValidateBoundVars`) - #163632 (bump rustc-build-sysroot) - #163635 (Revert note about signum of NaN) - #163644 (Add mailmap entry) - #163651 (Remove variants from `feature-gate-autodiff-use` test)

JonathanBrouwer · 2026-10-02T14:07:42Z

💔 I suspect this PR failed tests as part of a rollup
@bors r-

After fixing the problem, consider running a try job for the failed job before re-approving.

Link to failure: #163650 (comment)

@bors try jobs=test-x86_64-mingw-1

rust-bors · 2026-10-02T14:07:51Z

This pull request was unapproved.

This PR was contained in a rollup (#163656), which was unapproved.

View changes since this unapproval

bjorn3 · 2026-10-08T10:14:31Z

Reverted some changes that turned out needed to be reverted anyway in the follow up PR.

@bors try jobs=test-x86_64-mingw-1

Fix incremental compilation for fat LTO try-job: test-x86_64-mingw-1

rust-bors · 2026-10-08T11:59:38Z

💔 Test for d316683 failed: CI. Failed job:

try - test-x86_64-mingw-1 (web logs, enhanced plaintext logs)

These artifacts are never actually used. Only the pre-LTO artifacts would be useful, but caching that seems a bit more tricky and is not that important for now. Fat LTO itself is very slow anyway.

bjorn3 · 2026-10-20T13:37:33Z

When reproducing the MinGW failure, I noticed that the PR was accidentally also caching the bitcode of dependencies in the incr comp cache, which doesn't have any benefit. I've removed the support for pre-LTO caching for fat LTO from this PR for now. So this PR now only does refactorings and removes the useless post-LTO artifact caching for fat LTO. I've confirmed that the test that previously failed on MinGW now passes.

@rustbot ready

nnethercote · 2026-10-20T14:41:34Z

@bors r+

rust-bors · 2026-10-20T14:41:37Z

📌 Commit 51e5451 has been tentatively approved by nnethercote

It will be put into the queue for this repository once PR CI succeeds.

Stop useless caching of post-LTO artifact caching for fat LTO These artifacts are never actually used. Only the pre-LTO artifacts would be useful, but caching that seems a bit more tricky and is not that important for now. Fat LTO itself is very slow anyway. Also move incr comp session dirs out of `CodegenContext`. `CodegenContext` will in the future be serialized and deserialized into a different rustc instance when `-Zno-link`/`-Zlink-only` is used. A separate incr comp session has to be used for both rustc invocations. Part of rust-lang/compiler-team#908

…uwer Rollup of 19 pull requests Successful merges: - #163664 (Add new `RUSTC_BOOTSTRAP=-allow-unstable-compiler-flags` mode for testing stable compiler behavior in UI tests) - #163668 (Remap syntax contexts and expansion ids for det. metadata encoding) - #160404 (fd-views: AsRef<File>&Co. for BorrowedFd) - #163104 ([debuginfo] Emit `usize` and `isize` as typedefs) - #163317 (Stop useless caching of post-LTO artifact caching for fat LTO) - #163701 (add ReadDir::dir to get the directory handle of the underlying directory) - #164488 (Don't try to skip anything in `Skip::advance_by(0)`) - #164507 (Encode HashMap and HashSet in deterministic order when an encoder requires determinism) - #164611 (Improve bit permutation codegen) - #164612 (std: Combine `is_powerpc64_feature_detected` into `is_powerpc_feature_detected`) - #148842 (Avoid incorrect lifetime suggestion involving `sym::anon`) - #162668 (document that `!` does bitwise and logical negation) - #164264 (lint: suggest `fXX::is_nan` for unsuffixed NaN comparisons) - #164509 (layout invariant: turn delayed bug back into proper assertion) - #164540 (Minor optimizations around macro parsing) - #164594 (rustdoc: Correctly handle inner `deprecated` attribute on modules) - #164595 (Allow attributes in function trait parameters) - #164641 (Stabilize `slice_split_once`) - #164646 (Adjust rustfmt subtree sync docs to not use `--allow-noop` for now)

Rollup of 20 pull requests Successful merges: - #163664 (Add new `RUSTC_BOOTSTRAP=-allow-unstable-compiler-flags` mode for testing stable compiler behavior in UI tests) - #163668 (Remap syntax contexts and expansion ids for det. metadata encoding) - #163104 ([debuginfo] Emit `usize` and `isize` as typedefs) - #163317 (Stop useless caching of post-LTO artifact caching for fat LTO) - #163701 (add ReadDir::dir to get the directory handle of the underlying directory) - #164488 (Don't try to skip anything in `Skip::advance_by(0)`) - #164507 (Encode HashMap and HashSet in deterministic order when an encoder requires determinism) - #164611 (Improve bit permutation codegen) - #164612 (std: Combine `is_powerpc64_feature_detected` into `is_powerpc_feature_detected`) - #148842 (Avoid incorrect lifetime suggestion involving `sym::anon`) - #162668 (document that `!` does bitwise and logical negation) - #164264 (lint: suggest `fXX::is_nan` for unsuffixed NaN comparisons) - #164509 (layout invariant: turn delayed bug back into proper assertion) - #164540 (Minor optimizations around macro parsing) - #164594 (rustdoc: Correctly handle inner `deprecated` attribute on modules) - #164595 (Allow attributes in function trait parameters) - #164616 (Add test for VecDeque with a custom allocator) - #164629 (arch::breakpoint: avoid confusing 'equivalent' terminology) - #164641 (Stabilize `slice_split_once`) - #164646 (Adjust rustfmt subtree sync docs to not use `--allow-noop` for now)

Rollup merge of #163317 - bjorn3:lto_refactors22, r=nnethercote Stop useless caching of post-LTO artifact caching for fat LTO These artifacts are never actually used. Only the pre-LTO artifacts would be useful, but caching that seems a bit more tricky and is not that important for now. Fat LTO itself is very slow anyway. Also move incr comp session dirs out of `CodegenContext`. `CodegenContext` will in the future be serialized and deserialized into a different rustc instance when `-Zno-link`/`-Zlink-only` is used. A separate incr comp session has to be used for both rustc invocations. Part of rust-lang/compiler-team#908

Rollup of 20 pull requests Successful merges: - rust-lang/rust#163664 (Add new `RUSTC_BOOTSTRAP=-allow-unstable-compiler-flags` mode for testing stable compiler behavior in UI tests) - rust-lang/rust#163668 (Remap syntax contexts and expansion ids for det. metadata encoding) - rust-lang/rust#163104 ([debuginfo] Emit `usize` and `isize` as typedefs) - rust-lang/rust#163317 (Stop useless caching of post-LTO artifact caching for fat LTO) - rust-lang/rust#163701 (add ReadDir::dir to get the directory handle of the underlying directory) - rust-lang/rust#164488 (Don't try to skip anything in `Skip::advance_by(0)`) - rust-lang/rust#164507 (Encode HashMap and HashSet in deterministic order when an encoder requires determinism) - rust-lang/rust#164611 (Improve bit permutation codegen) - rust-lang/rust#164612 (std: Combine `is_powerpc64_feature_detected` into `is_powerpc_feature_detected`) - rust-lang/rust#148842 (Avoid incorrect lifetime suggestion involving `sym::anon`) - rust-lang/rust#162668 (document that `!` does bitwise and logical negation) - rust-lang/rust#164264 (lint: suggest `fXX::is_nan` for unsuffixed NaN comparisons) - rust-lang/rust#164509 (layout invariant: turn delayed bug back into proper assertion) - rust-lang/rust#164540 (Minor optimizations around macro parsing) - rust-lang/rust#164594 (rustdoc: Correctly handle inner `deprecated` attribute on modules) - rust-lang/rust#164595 (Allow attributes in function trait parameters) - rust-lang/rust#164616 (Add test for VecDeque with a custom allocator) - rust-lang/rust#164629 (arch::breakpoint: avoid confusing 'equivalent' terminology) - rust-lang/rust#164641 (Stabilize `slice_split_once`) - rust-lang/rust#164646 (Adjust rustfmt subtree sync docs to not use `--allow-noop` for now)

rustbot assigned mejrs Sep 25, 2026

bjorn3 mentioned this pull request Sep 25, 2026

Move LTO from the codegen coordinator thread to link_binary rust-lang/compiler-team#908

Closed

15 of 22 tasks

This comment has been minimized.

Sign in to view

bjorn3 force-pushed the lto_refactors22 branch from bc690ff to 980f03b Compare September 25, 2026 12:10

bjorn3 commented Sep 25, 2026

View reviewed changes

bjorn3 changed the title ~~Fix incr comp for fat LTO~~ Fix incremental compilation for fat LTO Sep 27, 2026

mejrs reviewed Sep 30, 2026

View reviewed changes

Comment thread compiler/rustc_codegen_llvm/src/back/llvm_backend.rs

rustbot assigned nnethercote and unassigned mejrs Sep 30, 2026

nnethercote approved these changes Oct 2, 2026

View reviewed changes

nnethercote added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Oct 2, 2026

rust-bors Bot 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-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Oct 2, 2026

JonathanBrouwer mentioned this pull request Oct 2, 2026

Rollup of 8 pull requests #163650

Closed

JonathanBrouwer mentioned this pull request Oct 2, 2026

Rollup of 13 pull requests #163656

Closed

rust-bors Bot added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. labels Oct 2, 2026

bjorn3 force-pushed the lto_refactors22 branch from 993bdd7 to 5951d04 Compare October 8, 2026 10:13

This comment has been minimized.

Sign in to view

rust-bors Bot pushed a commit that referenced this pull request Oct 8, 2026

Auto merge of #163317 - bjorn3:lto_refactors22, r=<try>

d316683

Fix incremental compilation for fat LTO try-job: test-x86_64-mingw-1

This comment has been minimized.

Sign in to view

bjorn3 added 2 commits October 20, 2026 15:07

Add test for incr comp fat LTO and fix assert_module_sources testing

1d19690

Stop useless caching of post-LTO artifact caching for fat LTO

51e5451

These artifacts are never actually used. Only the pre-LTO artifacts would be useful, but caching that seems a bit more tricky and is not that important for now. Fat LTO itself is very slow anyway.

bjorn3 force-pushed the lto_refactors22 branch from 5951d04 to 51e5451 Compare October 20, 2026 13:33

bjorn3 changed the title ~~Fix incremental compilation for fat LTO~~ Stop useless caching of post-LTO artifact caching for fat LTO Oct 20, 2026

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 20, 2026

rust-bors Bot 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 20, 2026

JonathanBrouwer mentioned this pull request Oct 20, 2026

Rollup of 19 pull requests #164658

Closed

jhpratt mentioned this pull request Oct 21, 2026

Rollup of 20 pull requests #164662

Merged

rust-bors Bot merged commit b384351 into rust-lang:main Oct 21, 2026
14 checks passed

rustbot added this to the 1.101.0 milestone Oct 21, 2026

bjorn3 deleted the lto_refactors22 branch October 21, 2026 07:56

github-actions Bot mentioned this pull request Oct 22, 2026

Toolchain upgrade to nightly-2026-10-22 flux-rs/flux#1847

Draft

Conversation

bjorn3 commented Sep 25, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

rustbot commented Sep 25, 2026

Uh oh!

rustbot commented Sep 25, 2026

Uh oh!

This comment has been minimized.

bjorn3 Sep 25, 2026 • 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!

mejrs 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!

Uh oh!

nnethercote 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!

Uh oh!

nnethercote Oct 2, 2026

Choose a reason for hiding this comment

Uh oh!

bjorn3 Oct 2, 2026

Choose a reason for hiding this comment

Uh oh!

bjorn3 commented Oct 2, 2026

Uh oh!

rust-bors Bot commented Oct 2, 2026

Uh oh!

JonathanBrouwer commented Oct 2, 2026

Uh oh!

rust-bors Bot commented Oct 2, 2026

Uh oh!

bjorn3 commented Oct 8, 2026

Uh oh!

This comment has been minimized.

rust-bors Bot commented Oct 8, 2026

Uh oh!

This comment has been minimized.

bjorn3 commented Oct 20, 2026

Uh oh!

nnethercote commented Oct 20, 2026

Uh oh!

rust-bors Bot commented Oct 20, 2026

Uh oh!

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

6 participants

bjorn3 commented Sep 25, 2026 •

edited

Loading

bjorn3 Sep 25, 2026 •

edited by rustbot

Loading

mejrs left a comment •

edited by rustbot

Loading

nnethercote left a comment •

edited by rustbot

Loading