From f1ae5314bef94f1defe868cb5d78d15b5da31c8c Mon Sep 17 00:00:00 2001 From: Mark Rousskov Date: Sun, 14 Apr 2024 11:15:00 -0400 Subject: Avoid reloading Vec::len across grow_one in push This saves an extra load from memory. --- library/alloc/src/vec/mod.rs | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) (limited to 'library/alloc/src/vec') diff --git a/library/alloc/src/vec/mod.rs b/library/alloc/src/vec/mod.rs index 1930be65bfb..b2e22d8715a 100644 --- a/library/alloc/src/vec/mod.rs +++ b/library/alloc/src/vec/mod.rs @@ -1991,15 +1991,17 @@ impl Vec { #[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; } } -- cgit 1.4.1-3-g733a5