cmGlobalGenerator: Optimize FindMakefile method with an index

This method is used by directory get/set APIs.  With the new
`SUBDIRECTORIES` and `BUILDSYSTEM_TARGETS` methods projects may now make
heavy use of these APIs to traverse their directory structure and
process targets.  Make this faster by indexing the directory lookups.

Source/cmGlobalGenerator.cxx

@@ -1059,6 +1059,7 @@ void cmGlobalGenerator::Configure()
 
   cmMakefile* dirMf = new cmMakefile(this, snapshot);
   this->Makefiles.push_back(dirMf);
+  this->IndexMakefile(dirMf);
 
   this->BinaryDirectories.insert(
     this->CMakeInstance->GetHomeOutputDirectory());
@@ -1528,6 +1529,7 @@ void cmGlobalGenerator::ClearGeneratorMembers()
   this->TargetDependencies.clear();
   this->TargetSearchIndex.clear();
   this->GeneratorTargetSearchIndex.clear();
+  this->MakefileSearchIndex.clear();
   this->ProjectMap.clear();
   this->RuleHashes.clear();
   this->DirectoryContentMap.clear();
@@ -1805,6 +1807,7 @@ std::string cmGlobalGenerator::GenerateCMakeBuildCommand(
 void cmGlobalGenerator::AddMakefile(cmMakefile* mf)
 {
   this->Makefiles.push_back(mf);
+  this->IndexMakefile(mf);
 
   // update progress
   // estimate how many lg there will be
@@ -1962,12 +1965,9 @@ void cmGlobalGenerator::FillProjectMap()
 
 cmMakefile* cmGlobalGenerator::FindMakefile(const std::string& start_dir) const
 {
-  for (std::vector<cmMakefile*>::const_iterator it = this->Makefiles.begin();
+  MakefileMap::const_iterator i = this->MakefileSearchIndex.find(start_dir);
-       it != this->Makefiles.end(); ++it) {
+  if (i != this->MakefileSearchIndex.end()) {
-    std::string sd = (*it)->GetCurrentSourceDirectory();
+    return i->second;
-    if (sd == start_dir) {
-      return *it;
-    }
   }
   return CM_NULLPTR;
 }
@@ -2012,6 +2012,17 @@ void cmGlobalGenerator::IndexGeneratorTarget(cmGeneratorTarget* gt)
   }
 }
 
+void cmGlobalGenerator::IndexMakefile(cmMakefile* mf)
+{
+  // FIXME: add_subdirectory supports multiple build directories
+  // sharing the same source directory.  We currently index only the
+  // first one, because that is what FindMakefile has always returned.
+  // All of its callers will need to be modified to support looking
+  // up directories by build directory path.
+  this->MakefileSearchIndex.insert(
+    MakefileMap::value_type(mf->GetCurrentSourceDirectory(), mf));
+}
+
 cmTarget* cmGlobalGenerator::FindTargetImpl(std::string const& name) const
 {
   TargetMap::const_iterator i = this->TargetSearchIndex.find(name);

Source/cmGlobalGenerator.h

@@ -462,13 +462,16 @@ private:
   typedef std::unordered_map<std::string, cmTarget*> TargetMap;
   typedef std::unordered_map<std::string, cmGeneratorTarget*>
     GeneratorTargetMap;
+  typedef std::unordered_map<std::string, cmMakefile*> MakefileMap;
 #else
   typedef cmsys::hash_map<std::string, cmTarget*> TargetMap;
   typedef cmsys::hash_map<std::string, cmGeneratorTarget*> GeneratorTargetMap;
+  typedef cmsys::hash_map<std::string, cmMakefile*> MakefileMap;
 #endif
 #else
   typedef std::map<std::string, cmTarget*> TargetMap;
   typedef std::map<std::string, cmGeneratorTarget*> GeneratorTargetMap;
+  typedef std::map<std::string, cmMakefile*> MakefileMap;
 #endif
   // Map efficiently from target name to cmTarget instance.
   // Do not use this structure for looping over all targets.
@@ -476,6 +479,11 @@ private:
   TargetMap TargetSearchIndex;
   GeneratorTargetMap GeneratorTargetSearchIndex;
 
+  // Map efficiently from source directory path to cmMakefile instance.
+  // Do not use this structure for looping over all directories.
+  // It may not contain all of them (see note in IndexMakefile method).
+  MakefileMap MakefileSearchIndex;
+
   cmMakefile* TryCompileOuterMakefile;
   // If you add a new map here, make sure it is copied
   // in EnableLanguagesFromGenerator
@@ -528,6 +536,8 @@ private:
 
   void ClearGeneratorMembers();
 
+  void IndexMakefile(cmMakefile* mf);
+
   virtual const char* GetBuildIgnoreErrorsFlag() const { return CM_NULLPTR; }
 
   // Cache directory content and target files to be built.