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gfx: Micro-optimize DList and StackingContext a bit.

Browse source 
I'm sad to say that this improved performance significantly. A lot of
this win is due to the Rust compiler not being smart about not zeroing
objects out if it doesn't need to.
This commit is contained in:
Patrick Walton 2014-11-05 00:51:21 -08:00
parent ffae110498
commit bdab68ab60
2 changed files with 50 additions and 49 deletions
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47
components/util/dlist.rs
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@ -10,13 +10,13 @@ use std::ptr;
struct RawDList<T> {
length: uint,
head: Option<Box<RawNode<T>>>,
head: *mut RawNode<T>,
tail: *mut RawNode<T>,
}
#[allow(dead_code)]
struct RawNode<T> {
next: Option<Box<RawNode<T>>>,
next: *mut RawNode<T>,
prev: *mut RawNode<T>,
value: T,
}
@ -38,27 +38,32 @@ pub fn split<T>(list: &mut DList<T>) -> DList<T> {
if list.length == 0 {
fail!("split_dlist(): empty list")
}
let mut head_node = mem::replace(&mut list.head, None);
let head_node_ptr: *mut RawNode<T> = &mut **head_node.as_mut().unwrap();
let mut head_list = RawDList {
let head_node = mem::replace(&mut list.head, ptr::null_mut());
let head_list = RawDList {
length: 1,
head: head_node,
tail: head_node_ptr,
tail: head_node,
};
debug_assert!(list.head.is_none());
mem::swap(&mut head_list.head.as_mut().unwrap().next, &mut list.head);
debug_assert!(head_list.head.as_mut().unwrap().next.is_none());
debug_assert!(head_list.head.as_mut().unwrap().prev.is_null());
head_list.head.as_mut().unwrap().prev = ptr::null_mut();
debug_assert!(list.head.is_null());
unsafe {
mem::swap(&mut (*head_list.head).next, &mut list.head);
debug_assert!((*head_list.head).next.is_null());
debug_assert!((*head_list.head).prev.is_null());
(*head_list.head).prev = ptr::null_mut();
}
list.length -= 1;
if list.length == 0 {
list.tail = ptr::null_mut()
} else {
if list.length == 1 {
list.tail = &mut **list.head.as_mut().unwrap() as *mut RawNode<T>
list.tail = list.head
}
unsafe {
(*list.head).prev = ptr::null_mut()
}
list.head.as_mut().unwrap().prev = ptr::null_mut()
}
unsafe {
@ -73,19 +78,19 @@ pub fn append_from<T>(this: &mut DList<T>, other: &mut DList<T>) {
let this = mem::transmute::<&mut DList<T>,&mut RawDList<T>>(this);
let other = mem::transmute::<&mut DList<T>,&mut RawDList<T>>(other);
if this.length == 0 {
this.head = mem::replace(&mut other.head, None);
this.head = mem::replace(&mut other.head, ptr::null_mut());
this.tail = mem::replace(&mut other.tail, ptr::null_mut());
this.length = mem::replace(&mut other.length, 0);
return
}
(*this.tail).next = match mem::replace(&mut other.head, None) {
None => return,
Some(mut head) => {
head.prev = this.tail;
Some(head)
}
};
let old_other_head = mem::replace(&mut other.head, ptr::null_mut());
if old_other_head.is_null() {
return
}
(*old_other_head).prev = this.tail;
(*this.tail).next = old_other_head;
this.tail = mem::replace(&mut other.tail, ptr::null_mut());
this.length += other.length;
other.length = 0;