rustc: Don't zero out arena chunks with vec::from_elem; that's slow because it calls the glue.

pcwalton · pcwalton · commit 5ce3d35f4170 · 2012-03-29T08:41:25.000-07:00
diff --git a/src/libstd/arena.rs b/src/libstd/arena.rs
@@ -8,7 +8,9 @@ type chunk = {data: [u8], mut fill: uint};
 type arena = {mut chunks: list::list<@chunk>};
 
 fn chunk(size: uint) -> @chunk {
-    @{ data: vec::from_elem(size, 0u8), mut fill: 0u }
+    let mut v = [];
+    vec::reserve(v, size);
+    @{ data: v, mut fill: 0u }
 }
 
 fn arena_with_size(initial_size: uint) -> arena {

Original file line number	Diff line number	Diff line change
`@@ -8,7 +8,9 @@ type chunk = {data: [u8], mut fill: uint};`
`8`	`8`	`type arena = {mut chunks: list::list<@chunk>};`
`9`	`9`
`10`	`10`	`fn chunk(size: uint) -> @chunk {`
`11`		`- @{ data: vec::from_elem(size, 0u8), mut fill: 0u }`
	`11`	`+ let mut v = [];`
	`12`	`+ vec::reserve(v, size);`
	`13`	`+ @{ data: v, mut fill: 0u }`
`12`	`14`	`}`
`13`	`15`
`14`	`16`	`fn arena_with_size(initial_size: uint) -> arena {`