Remove -Zfuel. by cjgillot · Pull Request #115293 · rust-lang/rust

cjgillot · 2023-08-27T21:59:09Z

I'm not sure this feature is used. I only found 2 references in a google search, both referring to its introduction.

Meanwhile, it's a global mutable state, untracked by incremental compilation, so incompatible with it.

rustbot · 2023-08-27T21:59:14Z

r? @wesleywiser

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rustbot · 2023-08-27T21:59:16Z

Some changes occurred to MIR optimizations

cc @rust-lang/wg-mir-opt

tmiasko · 2023-08-27T22:09:49Z

I found it quite useful in the past for bisecting bugs (it could be declared incompatible with incremental compilation if that aspect is an issue).

JakobDegen · 2023-08-27T23:27:54Z

I agree we should remove it right now, primarily because it's usefulness is significantly diminished by inconsistent use. At some point in the future we should switch to more structured transformations (as opposed to writing to &muts) in which case this can be brought back and we can enforce consistent usage

bors · 2023-08-29T16:41:36Z

☔ The latest upstream changes (presumably #112775) made this pull request unmergeable. Please resolve the merge conflicts.

bors · 2023-09-13T16:33:30Z

☔ The latest upstream changes (presumably #115803) made this pull request unmergeable. Please resolve the merge conflicts.

bors · 2023-09-21T14:05:29Z

☔ The latest upstream changes (presumably #116027) made this pull request unmergeable. Please resolve the merge conflicts.

bors · 2023-09-27T00:13:53Z

☔ The latest upstream changes (presumably #116144) made this pull request unmergeable. Please resolve the merge conflicts.

wesleywiser · 2023-10-05T14:29:37Z

Similar to @tmiasko, I've also found this useful in the past. The point that this is inconsistently used is true, but wouldn't it be better to fix that than to remove it entirely?

@pnkfelix suggested that attempting to use -Zfuel with incremental compilation enabled could generate a warning so that devs know it could lead to other problems.

cjgillot · 2023-10-05T14:53:40Z

We now have a more reliable way to disable optimizations: -Zmir-enable-passes. I recommend using that one for debugging.

bors · 2023-10-13T02:36:46Z

☔ The latest upstream changes (presumably #115964) made this pull request unmergeable. Please resolve the merge conflicts.

workingjubilee · 2023-10-17T18:28:37Z

It is more important that the information in the rustc-dev-guide is actually up-to-date, and that "how to debug optimization" is easy and accurate, as people try to actually use it e.g. to analyze and debug their codegen problems. By holding on to this, we are advising much more inexperienced devs to try to make sense of a de facto useless option.

So, do we want random passerby to try to use -Zfuel because we still document it as the thing to do, or do we want them to be informed as to what actually works? If we want -Zfuel to actually work, where is the PR?

wesleywiser

r=me with a corresponding PR to adjust rustc-dev-guide

tmiasko · 2023-11-11T00:27:28Z

The -Zfuel can be used to bisect specific transformation that is incorrect. It makes it trivial to generate diff between working and broken MIR. To locate the source code that is being miscompiled and extract minimized test case. The -Zmir-enable-passes is no alternative for such use cases.

It works perfectly fine even if not every single MIR optimizations uses it - just run bisection, dump MIR at the boundary, and diff between those. If for some reason the current inconsistent use is a deal breaker for others, I can prepare a pull request that will incorporate it directly into a pass manager.

I don't think we should remove it without a proper replacement.

bjorn3 · 2023-11-26T18:42:13Z

-Zfuel is entirely unreliable with parallel rustc, right? The order in which functions get mir optimizations running is non-deterministic and thus which function sees the last fuel consumed.

bors · 2024-08-19T09:58:49Z

☔ The latest upstream changes (presumably #129261) made this pull request unmergeable. Please resolve the merge conflicts.

bors · 2024-08-28T20:26:48Z

☔ The latest upstream changes (presumably #129691) made this pull request unmergeable. Please resolve the merge conflicts.

bors · 2024-09-03T03:58:55Z

☔ The latest upstream changes (presumably #129777) made this pull request unmergeable. Please resolve the merge conflicts.

nnethercote · 2024-09-04T21:28:28Z

It will be good to get this merged. I have some follow-up cleanups that rely on -Zfuel being removed :)

dianqk

It will be good to get this merged as well. I don’t use -Zfuel, and the reliability of this option still depends on whether we remember to call consider_optimizing.

dianqk · 2024-11-27T00:07:45Z

♥️
@bors r=wesleywiser,DianQK

dianqk · 2024-11-27T00:11:27Z

🧐

dianqk · 2024-11-27T00:11:43Z

@bors r=wesleywiser,DianQK

dianqk · 2024-11-27T00:13:37Z

@bors r=wesleywiser,DianQK

bors · 2024-11-27T00:13:40Z

📌 Commit 982cde9 has been approved by wesleywiser,DianQK

It is now in the queue for this repository.

…mpiler-errors Rollup of 8 pull requests Successful merges: - rust-lang#115293 (Remove -Zfuel.) - rust-lang#132605 (CI: increase timeout from 4h to 6h) - rust-lang#133304 (Revert diagnostics hack to fix ICE 132920) - rust-lang#133402 (Constify `Drop` and `Destruct`) - rust-lang#133458 (Fix `Result` and `Option` not getting a jump to def link generated) - rust-lang#133471 (gce: fix typing_mode mismatch) - rust-lang#133475 (`MaybeStorage` improvements) - rust-lang#133513 (Only ignore windows-gnu in avr-jmp-offset) r? `@ghost` `@rustbot` modify labels: rollup

Rollup merge of rust-lang#115293 - cjgillot:no-fuel, r=wesleywiser,DianQK Remove -Zfuel. I'm not sure this feature is used. I only found 2 references in a google search, both referring to its introduction. Meanwhile, it's a global mutable state, untracked by incremental compilation, so incompatible with it.

rustbot assigned wesleywiser Aug 27, 2023

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 Aug 27, 2023

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cjgillot force-pushed the no-fuel branch from 6fb3d35 to 3bb01f8Compare August 28, 2023 20:15

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cjgillot force-pushed the no-fuel branch from 3bb01f8 to 6d6c96fCompare August 28, 2023 20:24

rustbot added A-testsuite Area: The testsuite used to check the correctness of rustc T-bootstrap Relevant to the bootstrap subteam: Rust's build system (x.py and src/bootstrap) labels Aug 28, 2023

cjgillot force-pushed the no-fuel branch from 6d6c96f to 210e1f6Compare August 31, 2023 16:37

cjgillot force-pushed the no-fuel branch from 210e1f6 to c2c4119Compare September 13, 2023 16:55

cjgillot force-pushed the no-fuel branch from c2c4119 to 2a07e4fCompare September 21, 2023 16:20

cjgillot force-pushed the no-fuel branch from 2a07e4f to ac1c881Compare September 27, 2023 16:17

wesleywiser approved these changes Oct 24, 2023
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Dylan-DPC 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 Nov 6, 2023

cjgillot force-pushed the no-fuel branch from 7fc034e to a0306a7Compare August 18, 2024 12:09

cjgillot 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 Aug 19, 2024

cjgillot force-pushed the no-fuel branch from a0306a7 to 9d66485Compare August 22, 2024 02:25

cjgillot force-pushed the no-fuel branch from 9d66485 to 5a03448Compare September 1, 2024 16:57

dianqk approved these changes Nov 20, 2024
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cjgillot added 3 commits November 26, 2024 10:45

Remove -Zfuel.
7fa021a

Pacify tidy.
d013c18

Remove extra tests.
982cde9

cjgillot force-pushed the no-fuel branch from 5a03448 to 982cde9Compare November 26, 2024 10:46

dianqk closed this Nov 27, 2024

dianqk reopened this Nov 27, 2024

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 Nov 27, 2024

compiler-errors mentioned this pull request Nov 27, 2024
Rollup of 8 pull requests #133516
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bors merged commit 145df3b into rust-lang:masterNov 27, 2024

rustbot added this to the 1.85.0 milestone Nov 27, 2024

cjgillot deleted the no-fuel branch November 27, 2024 10:25

bjorn3 mentioned this pull request Feb 11, 2026
Implement opt-bisect-limit for MIR #152474
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