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Optimize vec::from_elem with manual inlining #6876

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Merged
merged 1 commit into from
Jun 1, 2013
Merged

Optimize vec::from_elem with manual inlining #6876

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18 changes: 15 additions & 3 deletions src/libstd/vec.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -149,8 +149,7 @@ pub fn from_fn<T>(n_elts: uint, op: old_iter::InitOp<T>) -> ~[T] {
do as_mut_buf(v) |p, _len| {
let mut i: uint = 0u;
while i < n_elts {
intrinsics::move_val_init(&mut(*ptr::mut_offset(p, i)),
op(i));
intrinsics::move_val_init(&mut(*ptr::mut_offset(p, i)), op(i));
i += 1u;
}
}
Expand All @@ -166,7 +165,20 @@ pub fn from_fn<T>(n_elts: uint, op: old_iter::InitOp<T>) -> ~[T] {
* to the value `t`.
*/
pub fn from_elem<T:Copy>(n_elts: uint, t: T) -> ~[T] {
from_fn(n_elts, |_i| copy t)
// hack: manually inline from_fn for 2x plus speedup (sadly very important, from_elem is a
// bottleneck in borrowck!)
unsafe {
let mut v = with_capacity(n_elts);
do as_mut_buf(v) |p, _len| {
let mut i = 0u;
while i < n_elts {
intrinsics::move_val_init(&mut(*ptr::mut_offset(p, i)), copy t);
i += 1u;
}
}
raw::set_len(&mut v, n_elts);
v
}
}

/// Creates a new unique vector with the same contents as the slice
Expand Down