Skip to content
New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Jump to bottom

update comment regarding TargetOptions.features #129863

Merged
merged 1 commit into from
Sep 5, 2024
Merged

update comment regarding TargetOptions.features #129863

merged 1 commit into from
Sep 5, 2024

Conversation

RalfJung
Copy link
Member

@RalfJung RalfJung commented Sep 1, 2024

The claim that -Ctarget-features cannot disable these features set in the target spec is definitely wrong -- I tried it for x86_64-pc-windows-gnu, which enables SSE3 that way. Building with -Ctarget-feature=-sse3 works fine, and cfg!(target_feature = "sse3") is false in that build.

There are also some indications that these are actually intended to be overwritten:

rust/compiler/rustc_target/src/spec/targets/i686_unknown_uefi.rs

Lines 22 to 23 in 3b14526

// If you initialize FP units yourself, you can override these flags with custom linker
// arguments, thus giving you access to full MMX/SSE acceleration.

rust/compiler/rustc_target/src/spec/targets/x86_64h_apple_darwin.rs

Lines 18 to 23 in 84ac80f

// FIXME: Sadly, turning these off here disables them in such a way that they
// aren't re-enabled by `-Ctarget-cpu=native` (on a machine that has them).
// It would be nice if this were not the case, but fixing it seems tricky
// (and given that the main use-case for this target is for use in universal
// binaries, probably not that important).
base.features = "-rdrnd,-aes,-pclmul,-rtm,-fsgsbase".into();

So... let's update the comment to match reality, I guess?

The claim that they overwrite -Ctarget-cpu is based on

  • for native, the comment in the apple target spec quoted above
  • for other CPU strings, the assumption that LLVMRustCreateTargetMachine will apply these features after doing whatever the base CPU model does. I am not sure how to check that, I hope some LLVM backend people can chime in. :)

@rustbot
Copy link
Collaborator

rustbot commented Sep 1, 2024

r? @wesleywiser

rustbot has assigned @wesleywiser.
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

@rustbot 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 Sep 1, 2024
@rustbot
Copy link
Collaborator

rustbot commented Sep 1, 2024

These commits modify compiler targets.
(See the Target Tier Policy.)

@RalfJung
Copy link
Member Author

RalfJung commented Sep 1, 2024 via email

@RalfJung
Copy link
Member Author

RalfJung commented Sep 1, 2024

LLVMRustCreateTargetMachine boils down to the createTargetMachine method on LLVM's TargetMachine class. The docs don't say whether the CPU or the Features take precedence... but I would expect it is the Features.

@wesleywiser
Copy link
Member

@bors r+ rollup

@bors
Copy link
Contributor

bors commented Sep 3, 2024

📌 Commit 5c0dfc6 has been approved by wesleywiser

It is now in the queue for this repository.

@bors 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 Sep 3, 2024
@matthiaskrgr matthiaskrgr mentioned this pull request Sep 3, 2024
Merged
bors added a commit to rust-lang-ci/rust that referenced this pull request Sep 3, 2024
@bors
Auto merge of rust-lang#129936 - matthiaskrgr:rollup-0s8xycb, r=matth…
76fb2c2 
…iaskrgr

Rollup of 9 pull requests

Successful merges:

 - rust-lang#127692 (Suggest `impl Trait` for References to Bare Trait in Function Header)
 - rust-lang#128701 (Don't Suggest Labeling `const` and `unsafe` Blocks )
 - rust-lang#128934 (Non-exhaustive structs may be empty)
 - rust-lang#129630 (Document the broken C ABI of `wasm32-unknown-unknown`)
 - rust-lang#129863 (update comment regarding TargetOptions.features)
 - rust-lang#129896 (do not attempt to prove unknowable goals)
 - rust-lang#129926 (Move `SanityCheck` and `MirPass`)
 - rust-lang#129928 (rustc_driver_impl: remove some old dead logic)
 - rust-lang#129930 (include 1.80.1 release notes on master)

r? `@ghost`
`@rustbot` modify labels: rollup
bors added a commit to rust-lang-ci/rust that referenced this pull request Sep 3, 2024
@bors
Auto merge of rust-lang#129936 - matthiaskrgr:rollup-0s8xycb, r=matth…
a257dd2 
…iaskrgr

Rollup of 9 pull requests

Successful merges:

 - rust-lang#127692 (Suggest `impl Trait` for References to Bare Trait in Function Header)
 - rust-lang#128701 (Don't Suggest Labeling `const` and `unsafe` Blocks )
 - rust-lang#128934 (Non-exhaustive structs may be empty)
 - rust-lang#129630 (Document the broken C ABI of `wasm32-unknown-unknown`)
 - rust-lang#129863 (update comment regarding TargetOptions.features)
 - rust-lang#129896 (do not attempt to prove unknowable goals)
 - rust-lang#129926 (Move `SanityCheck` and `MirPass`)
 - rust-lang#129928 (rustc_driver_impl: remove some old dead logic)
 - rust-lang#129930 (include 1.80.1 release notes on master)

r? `@ghost`
`@rustbot` modify labels: rollup
bors added a commit to rust-lang-ci/rust that referenced this pull request Sep 4, 2024
@bors
Auto merge of rust-lang#129936 - matthiaskrgr:rollup-0s8xycb, r=matth…
916e0e3 
…iaskrgr

Rollup of 9 pull requests

Successful merges:

 - rust-lang#127692 (Suggest `impl Trait` for References to Bare Trait in Function Header)
 - rust-lang#128701 (Don't Suggest Labeling `const` and `unsafe` Blocks )
 - rust-lang#128934 (Non-exhaustive structs may be empty)
 - rust-lang#129630 (Document the broken C ABI of `wasm32-unknown-unknown`)
 - rust-lang#129863 (update comment regarding TargetOptions.features)
 - rust-lang#129896 (do not attempt to prove unknowable goals)
 - rust-lang#129926 (Move `SanityCheck` and `MirPass`)
 - rust-lang#129928 (rustc_driver_impl: remove some old dead logic)
 - rust-lang#129930 (include 1.80.1 release notes on master)

r? `@ghost`
`@rustbot` modify labels: rollup
bors added a commit to rust-lang-ci/rust that referenced this pull request Sep 4, 2024
@bors
Auto merge of rust-lang#129936 - matthiaskrgr:rollup-0s8xycb, r=matth…
f59b9d8 
…iaskrgr

Rollup of 9 pull requests

Successful merges:

 - rust-lang#127692 (Suggest `impl Trait` for References to Bare Trait in Function Header)
 - rust-lang#128701 (Don't Suggest Labeling `const` and `unsafe` Blocks )
 - rust-lang#128934 (Non-exhaustive structs may be empty)
 - rust-lang#129630 (Document the broken C ABI of `wasm32-unknown-unknown`)
 - rust-lang#129863 (update comment regarding TargetOptions.features)
 - rust-lang#129896 (do not attempt to prove unknowable goals)
 - rust-lang#129926 (Move `SanityCheck` and `MirPass`)
 - rust-lang#129928 (rustc_driver_impl: remove some old dead logic)
 - rust-lang#129930 (include 1.80.1 release notes on master)

r? `@ghost`
`@rustbot` modify labels: rollup
bors added a commit to rust-lang-ci/rust that referenced this pull request Sep 4, 2024
@bors
Auto merge of rust-lang#129936 - matthiaskrgr:rollup-0s8xycb, r=matth…
ddb7c56 
…iaskrgr

Rollup of 9 pull requests

Successful merges:

 - rust-lang#127692 (Suggest `impl Trait` for References to Bare Trait in Function Header)
 - rust-lang#128701 (Don't Suggest Labeling `const` and `unsafe` Blocks )
 - rust-lang#128934 (Non-exhaustive structs may be empty)
 - rust-lang#129630 (Document the broken C ABI of `wasm32-unknown-unknown`)
 - rust-lang#129863 (update comment regarding TargetOptions.features)
 - rust-lang#129896 (do not attempt to prove unknowable goals)
 - rust-lang#129926 (Move `SanityCheck` and `MirPass`)
 - rust-lang#129928 (rustc_driver_impl: remove some old dead logic)
 - rust-lang#129930 (include 1.80.1 release notes on master)

r? `@ghost`
`@rustbot` modify labels: rollup
bors added a commit to rust-lang-ci/rust that referenced this pull request Sep 4, 2024
@bors
Auto merge of rust-lang#129936 - matthiaskrgr:rollup-0s8xycb, r=matth…
e158abf 
…iaskrgr

Rollup of 9 pull requests

Successful merges:

 - rust-lang#127692 (Suggest `impl Trait` for References to Bare Trait in Function Header)
 - rust-lang#128701 (Don't Suggest Labeling `const` and `unsafe` Blocks )
 - rust-lang#128934 (Non-exhaustive structs may be empty)
 - rust-lang#129630 (Document the broken C ABI of `wasm32-unknown-unknown`)
 - rust-lang#129863 (update comment regarding TargetOptions.features)
 - rust-lang#129896 (do not attempt to prove unknowable goals)
 - rust-lang#129926 (Move `SanityCheck` and `MirPass`)
 - rust-lang#129928 (rustc_driver_impl: remove some old dead logic)
 - rust-lang#129930 (include 1.80.1 release notes on master)

r? `@ghost`
`@rustbot` modify labels: rollup
bors added a commit to rust-lang-ci/rust that referenced this pull request Sep 4, 2024
@bors
Auto merge of rust-lang#129936 - matthiaskrgr:rollup-0s8xycb, r=matth…
009e738 
…iaskrgr

Rollup of 9 pull requests

Successful merges:

 - rust-lang#127692 (Suggest `impl Trait` for References to Bare Trait in Function Header)
 - rust-lang#128701 (Don't Suggest Labeling `const` and `unsafe` Blocks )
 - rust-lang#128934 (Non-exhaustive structs may be empty)
 - rust-lang#129630 (Document the broken C ABI of `wasm32-unknown-unknown`)
 - rust-lang#129863 (update comment regarding TargetOptions.features)
 - rust-lang#129896 (do not attempt to prove unknowable goals)
 - rust-lang#129926 (Move `SanityCheck` and `MirPass`)
 - rust-lang#129928 (rustc_driver_impl: remove some old dead logic)
 - rust-lang#129930 (include 1.80.1 release notes on master)

r? `@ghost`
`@rustbot` modify labels: rollup
@bors bors merged commit 2f6e855 into rust-lang:master Sep 5, 2024
6 checks passed
@rustbot rustbot added this to the 1.83.0 milestone Sep 5, 2024
rust-timer added a commit to rust-lang-ci/rust that referenced this pull request Sep 5, 2024
@rust-timer
Unrolled build for rust-lang#129863
c28fa0b 
Rollup merge of rust-lang#129863 - RalfJung:target-spec-features, r=wesleywiser

update comment regarding TargetOptions.features

The claim that `-Ctarget-features` cannot disable these features set in the target spec is definitely wrong -- I tried it for `x86_64-pc-windows-gnu`, which enables SSE3 that way. Building with `-Ctarget-feature=-sse3` works fine, and `cfg!(target_feature = "sse3")` is `false` in that build.

There are also some indications that these are actually intended to be overwritten:

https://github.com/rust-lang/rust/blob/3b14526cead4105f82c398d8d4c7954efa3bab6b/compiler/rustc_target/src/spec/targets/i686_unknown_uefi.rs#L22-L23

https://github.com/rust-lang/rust/blob/84ac80f1921afc243d71fd0caaa4f2838c294102/compiler/rustc_target/src/spec/targets/x86_64h_apple_darwin.rs#L18-L23

So... let's update the comment to match reality, I guess?

The claim that they overwrite `-Ctarget-cpu` is based on
- for `native`, the comment in the apple target spec quoted above
- for other CPU strings, the assumption that `LLVMRustCreateTargetMachine` will apply these features after doing whatever the base CPU model does. I am not sure how to check that, I hope some LLVM backend people can chime in. :)
@RalfJung RalfJung deleted the target-spec-features branch September 9, 2024 08:27
Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment
Reviewers

@wesleywiser wesleywiser wesleywiser approved these changes

Assignees

@wesleywiser wesleywiser

Labels
S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue.
Projects
None yet
Milestone
1.83.0
Development

Successfully merging this pull request may close these issues.
4 participants
@RalfJung @rustbot @wesleywiser @bors