From 4dbdadf94dbfa7eaf89e54d849ae6287de6b89c5 Mon Sep 17 00:00:00 2001
From: Vadim Petrochenkov <vadim.petrochenkov@gmail.com>
Date: Mon, 24 Feb 2020 19:03:15 +0300
Subject: [PATCH] rustc_metadata: Use binary search from standard library

instead of a hand rolled one.
---
 src/librustc_metadata/rmeta/decoder.rs | 18 +++++-------------
 1 file changed, 5 insertions(+), 13 deletions(-)

diff --git a/src/librustc_metadata/rmeta/decoder.rs b/src/librustc_metadata/rmeta/decoder.rs
index 01fd637b20e..3dacd2cbe95 100644
--- a/src/librustc_metadata/rmeta/decoder.rs
+++ b/src/librustc_metadata/rmeta/decoder.rs
@@ -408,20 +408,12 @@ impl<'a, 'tcx> SpecializedDecoder<Span> for DecodeContext<'a, 'tcx> {
             {
                 last_source_file
             } else {
-                let mut a = 0;
-                let mut b = imported_source_files.len();
+                let index = imported_source_files
+                    .binary_search_by_key(&lo, |source_file| source_file.original_start_pos)
+                    .unwrap_or_else(|index| index - 1);
 
-                while b - a > 1 {
-                    let m = (a + b) / 2;
-                    if imported_source_files[m].original_start_pos > lo {
-                        b = m;
-                    } else {
-                        a = m;
-                    }
-                }
-
-                self.last_source_file_index = a;
-                &imported_source_files[a]
+                self.last_source_file_index = index;
+                &imported_source_files[index]
             }
         };