Performance: Improve efficiency of source file lookup in cmMakefile

This reintroduces the change from commit v3.10.0-rc1~69^2 (Performance:
Improve efficiency of source file lookup in cmMakefile, 2017-08-17) with
some corrections.  The original was rolled back by commit
v3.10.0-rc1~52^2~1 (Revert "Performance: ...", 2017-09-25) due to
incompatibilities found.  The rollback was followed-up by addition of a
test for the offending case, and this revision passes the test.

1 files changed, 12 insertions, 1 deletions

diff --git a/Source/cmMakefile.h b/Source/cmMakefile.h
index 6867c02..7c27aef 100644
--- a/Source/cmMakefile.h
+++ b/Source/cmMakefile.h
@@ -821,7 +821,18 @@ protected:
   // libraries, classes, and executables
   mutable cmTargets Targets;
   std::map<std::string, std::string> AliasTargets;
-  std::vector<cmSourceFile*> SourceFiles;
+
+  typedef std::vector<cmSourceFile*> SourceFileVec;
+  SourceFileVec SourceFiles;
+
+  // Because cmSourceFile names are compared in a fuzzy way (see
+  // cmSourceFileLocation::Match()) we can't have a straight mapping from
+  // filename to cmSourceFile.  To make lookups more efficient we store the
+  // Name portion of the cmSourceFileLocation and then compare on the list of
+  // cmSourceFiles that might match that name.  Note that on platforms which
+  // have a case-insensitive filesystem we store the key in all lowercase.
+  typedef std::unordered_map<std::string, SourceFileVec> SourceFileMap;
+  SourceFileMap SourceFileSearchIndex;
 
   // Tests
   std::map<std::string, cmTest*> Tests;