[clang][lex] Avoid `DirectoryLookup` copies

This patch fixes a performance regression introduced in D121685 that was caused by copying `DirectoryLookup`.

rdar://101206790

Reviewed By: ributzka

Differential Revision: https://reviews.llvm.org/D136019

diff --git a/clang/lib/Lex/HeaderSearch.cpp b/clang/lib/Lex/HeaderSearch.cpp
index dd82f42..7230345 100644 (file)
--- a/clang/lib/Lex/HeaderSearch.cpp
+++ b/clang/lib/Lex/HeaderSearch.cpp
@@ -305,7 +305,7 @@ Module *HeaderSearch::lookupModule(StringRef ModuleName, StringRef SearchName,
 
   // Look through the various header search paths to load any available module
   // maps, searching for a module map that describes this module.
-  for (DirectoryLookup Dir : search_dir_range()) {
+  for (DirectoryLookup &Dir : search_dir_range()) {
     if (Dir.isFramework()) {
       // Search for or infer a module map for a framework. Here we use
       // SearchName rather than ModuleName, to permit finding private modules