cmTarget: Cache the cmSourceFiles in GetSourceFiles.

Avoid calling GetSourceFiles with the same result container multiple
times when tracing target dependencies.  The result from the previous
configuration is cached and used later otherwise.

Source/cmGeneratorTarget.cxx

@@ -636,19 +636,18 @@ cmTargetTraceDependencies
   // Queue all the source files already specified for the target.
   if (this->Target->GetType() != cmTarget::INTERFACE_LIBRARY)
     {
-    std::vector<std::string> sources;
     std::vector<std::string> configs;
     this->Makefile->GetConfigurations(configs);
     if (configs.empty())
       {
       configs.push_back("");
       }
+    std::set<std::string> emitted;
     for(std::vector<std::string>::const_iterator ci = configs.begin();
         ci != configs.end(); ++ci)
       {
+      std::vector<std::string> sources;
       this->Target->GetSourceFiles(sources, *ci);
-      }
-    std::set<std::string> emitted;
       for(std::vector<std::string>::const_iterator si = sources.begin();
           si != sources.end(); ++si)
         {
@@ -659,6 +658,7 @@ cmTargetTraceDependencies
           }
         }
       }
+    }
 
   // Queue pre-build, pre-link, and post-build rule dependencies.
   this->CheckCustomCommands(this->Target->GetPreBuildCommands());

Source/cmTarget.cxx

@@ -138,6 +138,10 @@ public:
                                                           LinkClosureMapType;
   LinkClosureMapType LinkClosureMap;
 
+  typedef std::map<TargetConfigPair, std::vector<cmSourceFile*> >
+                                                          SourceFilesMapType;
+  SourceFilesMapType SourceFilesMap;
+
   struct TargetPropertyEntry {
     TargetPropertyEntry(cmsys::auto_ptr<cmCompiledGeneratorExpression> cge,
       const std::string &targetName = std::string())
@@ -793,6 +797,18 @@ void cmTarget::GetSourceFiles(std::vector<cmSourceFile*> &files,
                               const std::string& config,
                               cmTarget const* head) const
 {
+
+  // Lookup any existing link implementation for this configuration.
+  TargetConfigPair key(head, cmSystemTools::UpperCase(config));
+
+  cmTargetInternals::SourceFilesMapType::iterator
+    it = this->Internal->SourceFilesMap.find(key);
+  if(it != this->Internal->SourceFilesMap.end())
+    {
+    files = it->second;
+    }
+  else
+    {
     std::vector<std::string> srcs;
     this->GetSourceFiles(srcs, config, head);
 
@@ -807,6 +823,8 @@ void cmTarget::GetSourceFiles(std::vector<cmSourceFile*> &files,
         files.push_back(sf);
         }
       }
+    this->Internal->SourceFilesMap[key] = files;
+    }
 }
 
 //----------------------------------------------------------------------------
@@ -835,6 +853,7 @@ void cmTarget::AddSources(std::vector<std::string> const& srcs)
     }
   if (!srcFiles.empty())
     {
+    this->Internal->SourceFilesMap.clear();
     cmListFileBacktrace lfbt;
     this->Makefile->GetBacktrace(lfbt);
     cmGeneratorExpression ge(lfbt);
@@ -969,6 +988,7 @@ cmSourceFile* cmTarget::AddSource(const std::string& src)
                    TargetPropertyEntryFinder(sfl))
                                       == this->Internal->SourceEntries.end())
     {
+    this->Internal->SourceFilesMap.clear();
     cmListFileBacktrace lfbt;
     this->Makefile->GetBacktrace(lfbt);
     cmGeneratorExpression ge(lfbt);
@@ -1738,6 +1758,7 @@ void cmTarget::SetProperty(const std::string& prop, const char* value)
       this->Makefile->IssueMessage(cmake::FATAL_ERROR, e.str());
       return;
       }
+    this->Internal->SourceFilesMap.clear();
     cmListFileBacktrace lfbt;
     this->Makefile->GetBacktrace(lfbt);
     cmGeneratorExpression ge(lfbt);
@@ -1824,7 +1845,7 @@ void cmTarget::AppendProperty(const std::string& prop, const char* value,
       this->Makefile->IssueMessage(cmake::FATAL_ERROR, e.str());
       return;
       }
-
+      this->Internal->SourceFilesMap.clear();
       cmListFileBacktrace lfbt;
       this->Makefile->GetBacktrace(lfbt);
       cmGeneratorExpression ge(lfbt);