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Avoid reloading Vec::len across grow_one in push

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This saves an extra load from memory.
This commit is contained in:
Mark Rousskov 2024-04-14 11:15:00 -04:00
parent c3ceb00281
commit f1ae5314be
2 changed files with 21 additions and 3 deletions
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8
library/alloc/src/vec/mod.rs
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@ -1991,15 +1991,17 @@ impl<T, A: Allocator> Vec<T, A> {
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_confusables("push_back", "put", "append")]
pub fn push(&mut self, value: T) {
// Inform codegen that the length does not change across grow_one().
let len = self.len;
// This will panic or abort if we would allocate > isize::MAX bytes
// or if the length increment would overflow for zero-sized types.
if self.len == self.buf.capacity() {
if len == self.buf.capacity() {
self.buf.grow_one();
}
unsafe {
let end = self.as_mut_ptr().add(self.len);
let end = self.as_mut_ptr().add(len);
ptr::write(end, value);
self.len += 1;
self.len = len + 1;
}
}