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Support RISC-V unaligned-scalar-mem target feature #110884

Merged
merged 1 commit into from
May 18, 2023
Merged

Support RISC-V unaligned-scalar-mem target feature #110884

merged 1 commit into from
May 18, 2023

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korran
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@korran korran commented Apr 27, 2023

This adds unaligned-scalar-mem as an allowed RISC-V target feature. Some RISC-V cores support unaligned access to memory without trapping. On such cores, the compiler could significantly improve code-size and performance when using functions like core::ptr::read_unaligned by emitting a single load or store instruction with an unaligned address, rather than a long sequence of byte load/store/bitmanip instructions.

Enabling the unaligned-scalar-mem target feature allows LLVM to do this optimization.

Fixes #110883

@korran
Support RISC-V unaligned-scalar-mem target feature
08f7e32 
This adds `unaligned-scalar-mem` as an allowed RISC-V target feature.
Some RISC-V cores support unaligned access to memory without trapping.
On such cores, the compiler could significantly improve code-size and
performance when using functions like core::ptr::read_unaligned<u32>
by emitting a single load or store instruction with an unaligned
address, rather than a long sequence of byte load/store/bitmanip
instructions.

Enabling the `unaligned-scalar-mem` target feature allows LLVM to do
this optimization.

Fixes rust-lang#110883
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rustbot commented Apr 27, 2023

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @b-naber (or someone else) soon.

Please see the contribution instructions for more information. Namely, in order to ensure the minimum review times lag, PR authors and assigned reviewers should ensure that the review label (S-waiting-on-review and S-waiting-on-author) stays updated, invoking these commands when appropriate:

  • @rustbot author: the review is finished, PR author should check the comments and take action accordingly
  • @rustbot review: the author is ready for a review, this PR will be queued again in the reviewer's queue

@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 Apr 27, 2023
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b-naber commented Apr 28, 2023

r? rust-lang/compiler

@rustbot rustbot assigned wesleywiser and unassigned b-naber Apr 28, 2023
@wesleywiser
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Thanks @korran!

@bors r+ rollup

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bors commented May 2, 2023

📌 Commit 08f7e32 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 May 2, 2023
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@bors r-

Just realized target features need T-lang signoff.

@bors bors 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 May 2, 2023
@wesleywiser
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@rustbot label +I-lang-nominated

This adds unaligned-scalar-mem as an allowed RISC-V target feature. Some RISC-V cores support unaligned access to memory without trapping. On such cores, the compiler could significantly improve code-size and performance when using functions like core::ptr::read_unaligned by emitting a single load or store instruction with an unaligned address, rather than a long sequence of byte load/store/bitmanip instructions.
Enabling the unaligned-scalar-mem target feature allows LLVM to do this optimization.

Nominating for T-lang sign off on adding this target feature.

Thanks!

@rustbot rustbot added the I-lang-nominated Nominated for discussion during a lang team meeting. label May 2, 2023
@nikomatsakis
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Would this be gated on nightly?

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Discussed in meeting. If this is gated on nightly, we are fine with adding it, and no FCP is required -- just unnominate.

If it will be insta-stable, we will rediscuss.

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Thanks @nikomatsakis! This is gated on the unstable riscv_target_feature feature.

@bors r+ rollup

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bors commented May 17, 2023

📌 Commit 08f7e32 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-author Status: This is awaiting some action (such as code changes or more information) from the author. labels May 17, 2023
@Dylan-DPC Dylan-DPC mentioned this pull request May 18, 2023
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bors added a commit to rust-lang-ci/rust that referenced this pull request May 18, 2023
@bors
Auto merge of rust-lang#111710 - Dylan-DPC:rollup-eutrx54, r=Dylan-DPC
9052ca9 
Rollup of 7 pull requests

Successful merges:

 - rust-lang#110884 (Support RISC-V unaligned-scalar-mem target feature)
 - rust-lang#111160 (Update serde in workspace and non-synced dependencies)
 - rust-lang#111168 (Specialize ToString implementation for fmt::Arguments)
 - rust-lang#111527 (add examples of port 0 binding behavior)
 - rust-lang#111561 (Include better context for "already exists" error in compiletest)
 - rust-lang#111633 (Avoid `&format("...")` calls in error message code.)
 - rust-lang#111679 (Remove libs message about ACPs from triagebot)

Failed merges:

r? `@ghost`
`@rustbot` modify labels: rollup
@bors bors merged commit 677da1c into rust-lang:master May 18, 2023
@rustbot rustbot added this to the 1.71.0 milestone May 18, 2023
@sethp sethp mentioned this pull request May 25, 2023
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@wesleywiser wesleywiser wesleywiser approved these changes

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I-lang-nominated Nominated for discussion during a lang team meeting. 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.
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Successfully merging this pull request may close these issues.

RISC-V LLVM feature +unaligned-scalar-mem not recognized by rustc
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@korran @rustbot @b-naber @wesleywiser @bors @nikomatsakis