From c5830686dea641b6efaec98607412c4ce204aff2 Mon Sep 17 00:00:00 2001
From: Raz Luvaton <16746759+rluvaton@users.noreply.github.com>
Date: Sat, 20 Sep 2025 22:05:38 +0300
Subject: [PATCH] perf: change `RawVec` `grow_one` from `#[inline(never)]` to
 `#[inline]`

I noticed that this was not inlined when trying to `push` and probably the reason why the compiler lose the information about the capacity (fixes https://github.com/rust-lang/rust/issues/82801)

BTW The original PR that added it (https://github.com/rust-lang/rust/pull/91352) wrote:
> [...] I tried lots of minor variations on this, e.g. different inlining
attributes. This was the best one I could find. [...]

I never contributed to Rust so I did not know how to test that it actually fixes the problem, but I'm fairly certain it is.

Consider the very basic example (Godbolt rustc 1.90.0 `-C opt-level=3 -C target-feature=+avx2 -C codegen-units=1`)
```rust
#[no_mangle]
fn extend_offsets(offsets: &[usize]) -> Vec::<usize> {
    let mut intermediate = Vec::<usize>::with_capacity(offsets.len());

    for &offset in offsets {
        intermediate.push(offset)
    }

    intermediate
}
```

it does not inline `grow_one` which make it not use SIMD.

If however we are using [`push_within_capacity`](https://github.com/rust-lang/rust/issues/100486):

```rust
#![feature(vec_push_within_capacity)]

#[no_mangle]
fn extend_offsets(offsets: &[usize]) -> Vec::<usize> {
    let mut intermediate = Vec::<usize>::with_capacity(offsets.len());

    for &offset in offsets {
        intermediate.push_within_capacity(offset).unwrap()
    }

    intermediate
}
```

it will use SIMD
---
 library/alloc/src/raw_vec/mod.rs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/library/alloc/src/raw_vec/mod.rs b/library/alloc/src/raw_vec/mod.rs
index b0027e964e467..d42e27cc3b405 100644
--- a/library/alloc/src/raw_vec/mod.rs
+++ b/library/alloc/src/raw_vec/mod.rs
@@ -334,7 +334,7 @@ impl<T, A: Allocator> RawVec<T, A> {
     /// A specialized version of `self.reserve(len, 1)` which requires the
     /// caller to ensure `len == self.capacity()`.
     #[cfg(not(no_global_oom_handling))]
-    #[inline(never)]
+    #[inline]
     #[track_caller]
     pub(crate) fn grow_one(&mut self) {
         self.inner.grow_one(T::LAYOUT)