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Optimize line offset parsing in <SourceFile as Decodable>::decode

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By inverting parsing loop, avoiding continually re-checking bytes_per_diff.
This commit is contained in:
Martin Gammelsæter 2022-04-12 16:31:03 +02:00
parent 4e1927db3c
commit 2b14529a7c
1 changed files with 20 additions and 11 deletions
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31
compiler/rustc_span/src/lib.rs
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@ -1318,17 +1318,26 @@ impl<D: Decoder> Decodable<D> for SourceFile {
let mut line_start: BytePos = Decodable::decode(d);
lines.push(line_start);
for _ in 1..num_lines {
let diff = match bytes_per_diff {
1 => d.read_u8() as u32,
2 => d.read_u16() as u32,
4 => d.read_u32(),
_ => unreachable!(),
};
line_start = line_start + BytePos(diff);
lines.push(line_start);
match bytes_per_diff {
1 => {
for _ in 1..num_lines {
line_start = line_start + BytePos(d.read_u8() as u32);
lines.push(line_start);
}
}
2 => {
for _ in 1..num_lines {
line_start = line_start + BytePos(d.read_u16() as u32);
lines.push(line_start);
}
}
4 => {
for _ in 1..num_lines {
line_start = line_start + BytePos(d.read_u32());
lines.push(line_start);
}
}
_ => unreachable!(),
}
}