Deprecate no-op codegen option `-Cinline-threshold=...` #124712

Enselic · 2024-05-04T15:27:31Z

This deprecates -Cinline-threshold since using it has no effect. This has been the case since the new LLVM pass manager started being used, more than 2 years ago.

Recommend using -Cllvm-args=--inline-threshold=... instead.

Closes #89742 which is E-help-wanted.

rustbot · 2024-05-04T15:27:39Z

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workingjubilee · 2024-05-04T19:35:54Z

compiler/rustc_session/src/options.rs

@@ -1502,7 +1502,8 @@ options! {
    incremental: Option<String> = (None, parse_opt_string, [UNTRACKED],
        "enable incremental compilation"),
    inline_threshold: Option<u32> = (None, parse_opt_number, [TRACKED],
-        "set the threshold for inlining a function"),
+        "this option is deprecated and does nothing \
+        (consider using `-Cllvm-args=--inline-threshold=...`)"),


Will this have any effect if they do?

Yes that makes a difference. Building e.g. libstd with -Cllvm-args=--inline-threshold=100000 vs -Cllvm-args=--inline-threshold=2 reliably makes a big difference in the size of .text, namely 1594 kB vs 367 kB:

$ RUSTFLAGS="-Ccodegen-units=1 -Cllvm-args=--inline-threshold=100000" ./x build --stage 0 library/std $ size ./build/x86_64-unknown-linux-gnu/stage0-std/x86_64-unknown-linux-gnu/release/libstd.rlib text ... 0 ... 1594437 ... $ RUSTFLAGS="-Ccodegen-units=1 -Cllvm-args=--inline-threshold=2" ./x build --stage 0 library/std $ size ./build/x86_64-unknown-linux-gnu/stage0-std/x86_64-unknown-linux-gnu/release/libstd.rlib text ... 0 ... 367682 ...

Another example is bat with 33 MB vs 5.4 MB:

$ RUSTFLAGS="-Cllvm-args=--inline-threshold=2" cargo build --release $ ls -hl target/release/bat -rwxr-xr-x 2 martin martin 5.4M May 5 10:58 target/release/bat $ RUSTFLAGS="-Cllvm-args=--inline-threshold=100000" cargo build --release $ ls -hl target/release/bat -rwxr-xr-x 2 martin martin 33M May 5 11:13 target/release/bat

Oh neat, I'm surprised it does anything!

ehuss · 2024-06-03T15:27:10Z

r? compiler

fmease

The GH issue had a fair bit of discussion and ppl seemed to have mostly settled on deprecation + warning. While you've obviously taken the NOP (+ doc) approach, emitting a warning or remapping it to -C llvm-args=-inline-threshold= are still valid options.

Emitting a warning would've likely prevented the odyssey as reported in #89742 (comment). Not a fan of non-lint warnings (i.e., ones that cannot be suppressed) but I think it would make perfect sense here. -Cno-stack-check emits a warning for example (-Car=... doesn't OTOH).

Regarding remapping to LLVM's "new"(?) inline-threshold I'm not well-versed enough in the matter to be able to give any input on that. Apart from semantic differences compared to the OldPM days (which seems to be the case having read the discussion), I guess another factor are the guarantees we (want to) provide for -C* flags esp. wrt. alternative codegen backends (codegen_{cranelift,gcc} are still unstable ofc). I don't know anything about that, so I'll let sb. else take a look at this PR.

fmease · 2024-06-13T09:04:46Z

I'm pretty sure this needs a compiler FCP, therefore:
r? compiler-team

fmease · 2024-06-13T09:21:29Z

compiler/rustc_session/src/options.rs

@@ -1502,7 +1502,8 @@ options! {
    incremental: Option<String> = (None, parse_opt_string, [UNTRACKED],
        "enable incremental compilation"),
    inline_threshold: Option<u32> = (None, parse_opt_number, [TRACKED],


TL;DR: If the deprecation ends up getting accepted (rather than the remapping), please emit a warning like -Cno-stack-check does (and unlike -Car=... which we might want to change in a separate PR).

Done, including regression test.

Note that I also added this commit to this PR:

commit 651ff643ae68438213bded335ef47cc9c50d3039 Author: Martin Nordholts <martin.nordholts@codetale.se> Date: Fri Jun 14 19:48:40 2024 +0200 Fix typo in `-Cno-stack-check` deprecation warning The flag `--no-stack-check` does not exist: $ rustc --no-stack-check error: Unrecognized option: 'no-stack-check'. Did you mean `-C no-stack-check`?

Enselic · 2024-06-14T04:19:26Z

remapping it to -C llvm-args=-inline-threshold=

Remapping would probably have been good in late 2021 instead of making -Cinline-threshold a no-op. If we do it now - almost three years later - it would arguable be just as surprising as when it stopped working.

Also, maintaining the mapping will be quite much work. There are several knobs in LLVM to tweak, and people will have opinions on how to do it. I foresee endless discussions on how we should do it exactly. And this problem is multiplied for each codegen backend. So given where we are today, I think it is best to not try to remap.

But emitting a warning like -Cno-stack-check does is a good idea. I will do that. Thanks for taking a look at my PR!

The flag `--no-stack-check` does not exist: $ rustc --no-stack-check error: Unrecognized option: 'no-stack-check'. Did you mean `-C no-stack-check`?

This deprecates `-Cinline-threshold` since using it has no effect. This has been the case since the new LLVM pass manager started being used, more than 2 years ago.

pnkfelix · 2024-06-24T14:03:44Z

i think our official process when it comes to changing the stable command line interface of rustc is the Major Change Proposal (MCP) process.

But this specific change strikes me largely as a bug fix where the PR author is trying to make the whole thing more coherent (while also making the actual change quite minimal), and I don't think it warrants an MCP.

So, I'm going to r+ (because I don't think we need to further delay landing this change), but I also am going to nominate this PR so that the T-compiler team can double-check whether I am right that there exists some CLI changes that do not warrant an MCP.

@bors r+

bors · 2024-06-24T14:03:47Z

📌 Commit f5f067b has been approved by pnkfelix

It is now in the queue for this repository.

pnkfelix · 2024-06-24T14:05:44Z

(as an example of why I nominated this, the T-compiler team might want to discuss the valid feedback left by @fmease , in order to determine whether an MCP was in fact warranted here.)

…mpiler-errors Rollup of 11 pull requests Successful merges: - rust-lang#124460 (Show notice about "never used" of Debug for enum) - rust-lang#124712 (Deprecate no-op codegen option `-Cinline-threshold=...`) - rust-lang#125082 (Remove `MaybeUninit::uninit_array()` and replace it with inline const blocks.) - rust-lang#125575 (SmartPointer derive-macro) - rust-lang#126413 (compiletest: make the crash test error message abit more informative) - rust-lang#126673 (Ensure we don't accidentally succeed when we want to report an error) - rust-lang#126682 (coverage: Overhaul validation of the `#[coverage(..)]` attribute) - rust-lang#126899 (Suggest inline const blocks for array initialization) - rust-lang#126904 (Small fixme in core now that NonZero is generic) - rust-lang#126909 (add `@kobzol` to bootstrap team for triagebot) - rust-lang#126911 (Split the lifetimes of `MirBorrowckCtxt`) r? `@ghost` `@rustbot` modify labels: rollup

Rollup merge of rust-lang#124712 - Enselic:deprecate-inline-threshold, r=pnkfelix Deprecate no-op codegen option `-Cinline-threshold=...` This deprecates `-Cinline-threshold` since using it has no effect. This has been the case since the new LLVM pass manager started being used, more than 2 years ago. Recommend using `-Cllvm-args=--inline-threshold=...` instead. Closes rust-lang#89742 which is E-help-wanted.

rustbot assigned JohnTitor May 4, 2024

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 May 4, 2024

workingjubilee reviewed May 4, 2024

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rustbot assigned fmease and unassigned JohnTitor Jun 3, 2024

fmease added the needs-fcp This change is insta-stable, so needs a completed FCP to proceed. label Jun 13, 2024

fmease reviewed Jun 13, 2024

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rustbot assigned pnkfelix and unassigned fmease Jun 13, 2024

fmease reviewed Jun 13, 2024

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rustc_codegen_ssa: Remove unused ModuleConfig::inline_threshold

3af6242

Enselic force-pushed the deprecate-inline-threshold branch from be39c26 to 97c67ee Compare June 14, 2024 18:18

Enselic changed the title ~~Deprecate codegen option inline-threshold~~ Deprecate no-op codegen option -Cinline-threshold=... Jun 14, 2024

Enselic added 2 commits June 14, 2024 20:21

Fix typo in -Cno-stack-check deprecation warning

651ff64

The flag `--no-stack-check` does not exist: $ rustc --no-stack-check error: Unrecognized option: 'no-stack-check'. Did you mean `-C no-stack-check`?

Deprecate no-op codegen option -Cinline-threshold=...

f5f067b

This deprecates `-Cinline-threshold` since using it has no effect. This has been the case since the new LLVM pass manager started being used, more than 2 years ago.

Enselic force-pushed the deprecate-inline-threshold branch from 97c67ee to f5f067b Compare June 14, 2024 18:26

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 Jun 24, 2024

pnkfelix added the I-compiler-nominated The issue / PR has been nominated for discussion during a compiler team meeting. label Jun 24, 2024

compiler-errors mentioned this pull request Jun 24, 2024

Rollup of 11 pull requests #126914

Merged

bors merged commit faa28be into rust-lang:master Jun 24, 2024
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rustbot added this to the 1.81.0 milestone Jun 24, 2024

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Deprecate no-op codegen option `-Cinline-threshold=...` #124712

Deprecate no-op codegen option `-Cinline-threshold=...` #124712

Enselic commented May 4, 2024 •

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Deprecate no-op codegen option -Cinline-threshold=... #124712

Deprecate no-op codegen option -Cinline-threshold=... #124712

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Deprecate no-op codegen option `-Cinline-threshold=...` #124712

Deprecate no-op codegen option `-Cinline-threshold=...` #124712

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