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Make intrinsic fallback bodies cross-crate inlineable #121309

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Feb 22, 2024

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This change was prompted by the stage1 compiler spending 4% of its time when compiling the polymorphic-recursion MIR opt test in unlikely.

Intrinsic fallback bodies like unlikely should always be inlined, it's very silly if they are not. To do this, we enable the fallback bodies to be cross-crate inlineable. Not that this matters for our workloads since the compiler never actually uses the "fallback bodies", it just uses whatever was cfg(bootstrap)ped, so I've also added #[inline] to those.

See the comments for more information.

r? oli-obk

@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. T-libs Relevant to the library team, which will review and decide on the PR/issue. labels Feb 19, 2024
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rustbot commented Feb 19, 2024

Some changes occurred to MIR optimizations

cc @rust-lang/wg-mir-opt

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This change was prompted by the stage1 compiler spending 4% of its time
when compiling the polymorphic-recursion MIR opt test in `unlikely`.

Intrinsic fallback bodies like `unlikely` should always be inlined, it's
very silly if they are not. To do this, we enable the fallback bodies to
be cross-crate inlineable. Not that this matters for our workloads since
the compiler never actually _uses_ the "fallback bodies", it just uses
whatever was cfg(bootstrap)ped, so I've also added `#[inline]` to those.
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oli-obk commented Feb 19, 2024

@bors r+

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bors commented Feb 19, 2024

📌 Commit 0f4925e has been approved by oli-obk

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 Feb 19, 2024
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bors commented Feb 22, 2024

⌛ Testing commit 0f4925e with merge 1bb3a9f...

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bors commented Feb 22, 2024

☀️ Test successful - checks-actions
Approved by: oli-obk
Pushing 1bb3a9f to master...

@bors bors added the merged-by-bors This PR was explicitly merged by bors. label Feb 22, 2024
@bors bors merged commit 1bb3a9f into rust-lang:master Feb 22, 2024
12 checks passed
@rustbot rustbot added this to the 1.78.0 milestone Feb 22, 2024
@Noratrieb Noratrieb deleted the inline-all-the-fallbacks branch February 22, 2024 14:49
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Finished benchmarking commit (1bb3a9f): comparison URL.

Overall result: ❌✅ regressions and improvements - no action needed

@rustbot label: -perf-regression

Instruction count

This is a highly reliable metric that was used to determine the overall result at the top of this comment.

mean range count
Regressions ❌
(primary)
- - 0
Regressions ❌
(secondary)
2.3% [2.3%, 2.3%] 1
Improvements ✅
(primary)
- - 0
Improvements ✅
(secondary)
-1.4% [-1.4%, -1.4%] 1
All ❌✅ (primary) - - 0

Max RSS (memory usage)

Results

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

mean range count
Regressions ❌
(primary)
- - 0
Regressions ❌
(secondary)
- - 0
Improvements ✅
(primary)
-3.7% [-3.7%, -3.7%] 1
Improvements ✅
(secondary)
- - 0
All ❌✅ (primary) -3.7% [-3.7%, -3.7%] 1

Cycles

This benchmark run did not return any relevant results for this metric.

Binary size

This benchmark run did not return any relevant results for this metric.

Bootstrap: 649.986s -> 649.076s (-0.14%)
Artifact size: 310.96 MiB -> 310.97 MiB (0.00%)

adpaco-aws added a commit to model-checking/kani that referenced this pull request Feb 29, 2024
Upgrades the Rust toolchain to `nightly-2024-02-25`. The Rust compiler
PRs that triggered changes in this upgrades are:
 * rust-lang/rust#121209
 * rust-lang/rust#121309
 * rust-lang/rust#120863
 * rust-lang/rust#117772
 * rust-lang/rust#117658

With rust-lang/rust#121309 some intrinsics
became inlineable so their names became qualified. This made our `match`
on the intrinsic name to fail in those cases, leaving them as
unsupported constructs as in this example:

```
warning: Found the following unsupported constructs:
             - _RNvNtCscyGW2MM2t5j_4core10intrinsics8unlikelyCs1eohKeNmpdS_5arith (3)
             - caller_location (1)
             - foreign function (1)
         
         Verification will fail if one or more of these constructs is reachable.
         See https://model-checking.github.io/kani/rust-feature-support.html for more details.

[...]

Failed Checks: _RNvNtCscyGW2MM2t5j_4core10intrinsics8unlikelyCs1eohKeNmpdS_5arith is not currently supported by Kani. Please post your example at https://github.com/model-checking/kani/issues/new/choose
 File: "/home/ubuntu/.rustup/toolchains/nightly-2024-02-18-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/num/mod.rs", line 25, in core::num::<impl i8>::checked_add
```

We use `trimmed_name()` to work around this, but that may include type
arguments if the intrinsic is defined on generics. So in those cases, we
just take the first part of the name so we can keep the rest as before.

Resolves #3044
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6 participants