Avoid adjusting file positions twice.

`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.

1 files changed, 4 insertions, 22 deletions

diff --git a/compiler/rustc_metadata/src/rmeta/decoder.rs b/compiler/rustc_metadata/src/rmeta/decoder.rs
index 4038af38a2c..1624e6cd6ee 100644
--- a/compiler/rustc_metadata/src/rmeta/decoder.rs
+++ b/compiler/rustc_metadata/src/rmeta/decoder.rs
@@ -1639,10 +1639,10 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
                         src_hash,
                         start_pos,
                         end_pos,
-                        mut lines,
-                        mut multibyte_chars,
-                        mut non_narrow_chars,
-                        mut normalized_pos,
+                        lines,
+                        multibyte_chars,
+                        non_narrow_chars,
+                        normalized_pos,
                         name_hash,
                         ..
                     } = source_file_to_import;
@@ -1679,24 +1679,6 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
 
                     let source_length = (end_pos - start_pos).to_usize();
 
-                    // Translate line-start positions and multibyte character
-                    // position into frame of reference local to file.
-                    // `SourceMap::new_imported_source_file()` will then translate those
-                    // coordinates to their new global frame of reference when the
-                    // offset of the SourceFile is known.
-                    for pos in &mut lines {
-                        *pos = *pos - start_pos;
-                    }
-                    for mbc in &mut multibyte_chars {
-                        mbc.pos = mbc.pos - start_pos;
-                    }
-                    for swc in &mut non_narrow_chars {
-                        *swc = *swc - start_pos;
-                    }
-                    for np in &mut normalized_pos {
-                        np.pos = np.pos - start_pos;
-                    }
-
                     let local_version = sess.source_map().new_imported_source_file(
                         name,
                         src_hash,