bjoernager/rust
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Avoid adjusting file positions twice.

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`imported_source_files` adjusts lots of file positions, and then calls
`new_imported_source_file`, which then adjust them all again. This
commit combines the two adjustments into one, for a small perf win.
This commit is contained in:
Nicholas Nethercote 2022-05-25 14:01:18 +10:00
parent 3e810c64d0
commit 2b91c40c19
2 changed files with 18 additions and 29 deletions
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21
compiler/rustc_span/src/source_map.rs
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@ -345,20 +345,27 @@ impl SourceMap {
let end_pos = Pos::from_usize(start_pos + source_len);
let start_pos = Pos::from_usize(start_pos);
// Translate these positions into the new global frame of reference,
// now that the offset of the SourceFile is known.
//
// These are all unsigned values. `original_start_pos` may be larger or
// smaller than `start_pos`, but `pos` is always larger than both.
// Therefore, `(pos - original_start_pos) + start_pos` won't overflow
// but `start_pos - original_start_pos` might. So we use the former
// form rather than pre-computing the offset into a local variable. The
// compiler backend can optimize away the repeated computations in a
// way that won't trigger overflow checks.
for pos in &mut file_local_lines {
*pos = *pos + start_pos;
*pos = (*pos - original_start_pos) + start_pos;
}
for mbc in &mut file_local_multibyte_chars {
mbc.pos = mbc.pos + start_pos;
mbc.pos = (mbc.pos - original_start_pos) + start_pos;
}
for swc in &mut file_local_non_narrow_chars {
*swc = *swc + start_pos;
*swc = (*swc - original_start_pos) + start_pos;
}
for nc in &mut file_local_normalized_pos {
nc.pos = nc.pos + start_pos;
nc.pos = (nc.pos - original_start_pos) + start_pos;
}
let source_file = Lrc::new(SourceFile {