Poor inlining of closures for vec::from_fn<T>() #6623
Description
When there are multiple calls to vec::from_fn<T>() with the same type T but different closures, the compiler chooses to generate only one copy of vec::from_fn<T>() and pass the closure as an argument. This is really bad for simple closures like the ones in vec::from_elem<int>() or vec::to_owned<int>()
extern mod std;
#[bench]
fn to_owned(b: &mut std::test::BenchHarness) {
let x = [0, ..1000];
do b.iter {
vec::to_owned(x);
}
}
#[bench]
fn from_elem(b: &mut std::test::BenchHarness) {
do b.iter {
vec::from_elem(1000, 0);
}
}
fn main() {
}Running these gives:
running 2 tests
test from_elem ... bench: 2060 ns/iter (+/- 0)
test to_owned ... bench: 2306 ns/iter (+/- 3)
But if I remove one of the functions and only keep the other, I get:
running 1 test
test from_elem ... bench: 425 ns/iter (+/- 3)
and
running 1 test
test to_owned ... bench: 883 ns/iter (+/- 0)
This causes a 10% performance hit for rustc --no-trans. 0m14.664s vs. 13.592s with from_elem modified not to call from_fn but having a literal copy of the code.