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rustc: Don't read both rlib and dylib metadata

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This is an optimization which is quite impactful for compiling small crates.
Reading libstd's metadata takes about 50ms, and a hello world before this change
took about 100ms (this change halves that time).

Recent changes made it such that this optimization wasn't performed, but I think
it's a better idea do to this for now. See #10786 for tracking this issue.
This commit is contained in:
Alex Crichton 2014-04-07 13:13:21 -07:00
parent 5367c32c7d
commit cced02fcac
1 changed files with 12 additions and 4 deletions
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16
src/librustc/metadata/loader.rs
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@ -317,15 +317,23 @@ impl<'a> Context<'a> {
// read the metadata from it if `*slot` is `None`. If the metadata couldn't
// be read, it is assumed that the file isn't a valid rust library (no
// errors are emitted).
//
// FIXME(#10786): for an optimization, we only read one of the library's
// metadata sections. In theory we should read both, but
// reading dylib metadata is quite slow.
fn extract_one(&mut self, m: HashSet<Path>, flavor: &str,
slot: &mut Option<MetadataBlob>) -> Option<Path> {
let mut ret = None::<Path>;
let mut error = 0;
if slot.is_some() {
// FIXME(#10786): for an optimization, we only read one of the
// library's metadata sections. In theory we should
// read both, but reading dylib metadata is quite
// slow.
if m.len() == 0 {
return None
} else if m.len() == 1 {
return Some(m.move_iter().next().unwrap())
}
}
for lib in m.move_iter() {
info!("{} reading metadata from: {}", flavor, lib.display());
let metadata = match get_metadata_section(self.os, &lib) {