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Rollup merge of #89546 - joshtriplett:grow-metadata-faster, r=petroch…
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…enkov

Make an initial guess for metadata size to reduce buffer resizes

When reading metadata, the compiler starts with a `Vec::new()`, which will need to grow repeatedly as the metadata gets decompressed into it. Reduce the number of resizes by starting out at the size of the compressed data.
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Manishearth authored Oct 5, 2021
2 parents e8f2cdd + c35a700 commit f1dab12
Showing 1 changed file with 3 additions and 1 deletion.
4 changes: 3 additions & 1 deletion compiler/rustc_metadata/src/locator.rs
Original file line number Diff line number Diff line change
Expand Up @@ -740,7 +740,9 @@ fn get_metadata_section(
// Header is okay -> inflate the actual metadata
let compressed_bytes = &buf[header_len..];
debug!("inflating {} bytes of compressed metadata", compressed_bytes.len());
let mut inflated = Vec::new();
// Assume the decompressed data will be at least the size of the compressed data, so we
// don't have to grow the buffer as much.
let mut inflated = Vec::with_capacity(compressed_bytes.len());
match FrameDecoder::new(compressed_bytes).read_to_end(&mut inflated) {
Ok(_) => rustc_erase_owner!(OwningRef::new(inflated).map_owner_box()),
Err(_) => {
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