Optimize custom command full-path dependency lookup

In the common case of custom command dependencies specified via full
path optimize the implementation of GetSourceFileWithOutput using a
(hash) map.  This is significantly faster than the existing linear
search.  In the non-full-path case fall back to the existing linear
suffix search.

Source/cmMakefile.cxx

@@ -150,6 +150,7 @@ cmMakefile::cmMakefile(const cmMakefile& mf): Internal(new Internals)
   this->Initialize();
   this->CheckSystemVars = mf.CheckSystemVars;
   this->ListFileStack = mf.ListFileStack;
+  this->OutputToSource = mf.OutputToSource;
 }
 
 //----------------------------------------------------------------------------
@@ -1010,10 +1011,31 @@ cmMakefile::AddCustomCommandToOutput(const std::vector<std::string>& outputs,
     cc->SetEscapeOldStyle(escapeOldStyle);
     cc->SetEscapeAllowMakeVars(true);
     file->SetCustomCommand(cc);
+    this->UpdateOutputToSourceMap(outputs, file);
     }
   return file;
 }
 
+//----------------------------------------------------------------------------
+void
+cmMakefile::UpdateOutputToSourceMap(std::vector<std::string> const& outputs,
+                                    cmSourceFile* source)
+{
+  for(std::vector<std::string>::const_iterator o = outputs.begin();
+      o != outputs.end(); ++o)
+    {
+    this->UpdateOutputToSourceMap(*o, source);
+    }
+}
+
+//----------------------------------------------------------------------------
+void
+cmMakefile::UpdateOutputToSourceMap(std::string const& output,
+                                    cmSourceFile* source)
+{
+  this->OutputToSource[output] = source;
+}
+
 //----------------------------------------------------------------------------
 cmSourceFile*
 cmMakefile::AddCustomCommandToOutput(const char* output,
@@ -1994,7 +2016,7 @@ cmMakefile::AddNewTarget(cmTarget::TargetType type, const char* name)
   return &it->second;
 }
 
-cmSourceFile *cmMakefile::GetSourceFileWithOutput(const char *cname)
+cmSourceFile *cmMakefile::LinearGetSourceFileWithOutput(const char *cname)
 {
   std::string name = cname;
   std::string out;
@@ -2030,6 +2052,25 @@ cmSourceFile *cmMakefile::GetSourceFileWithOutput(const char *cname)
   return 0;
 }
 
+cmSourceFile *cmMakefile::GetSourceFileWithOutput(const char *cname)
+{
+  std::string name = cname;
+
+  // If the queried path is not absolute we use the backward compatible
+  // linear-time search for an output with a matching suffix.
+  if(!cmSystemTools::FileIsFullPath(cname))
+    {
+    return LinearGetSourceFileWithOutput(cname);
+    }
+  // Otherwise we use an efficient lookup map.
+  OutputToSourceMap::iterator o = this->OutputToSource.find(name);
+  if (o != this->OutputToSource.end())
+    {
+    return (*o).second;
+    }
+  return 0;
+}
+
 #if defined(CMAKE_BUILD_WITH_CMAKE)
 cmSourceGroup* cmMakefile::GetSourceGroup(const std::vector<std::string>&name)
 {

Source/cmMakefile.h

@@ -29,6 +29,9 @@
 
 #include <cmsys/auto_ptr.hxx>
 #include <cmsys/RegularExpression.hxx>
+#if defined(CMAKE_BUILD_WITH_CMAKE)
+# include <cmsys/hash_map.hxx>
+#endif
 
 class cmFunctionBlocker;
 class cmCommand;
@@ -1039,6 +1042,26 @@ private:
 
   bool GeneratingBuildSystem;
 
+  /**
+   * Old version of GetSourceFileWithOutput(const char*) kept for
+   * backward-compatibility. It implements a linear search and support
+   * relative file paths. It is used as a fall back by
+   * GetSourceFileWithOutput(const char*).
+   */
+  cmSourceFile *LinearGetSourceFileWithOutput(const char *cname);
+
+  // A map for fast output to input look up.
+#if defined(CMAKE_BUILD_WITH_CMAKE)
+  typedef cmsys::hash_map<std::string, cmSourceFile*> OutputToSourceMap;
+#else
+  typedef std::map<std::string, cmSourceFile*> OutputToSourceMap;
+#endif
+  OutputToSourceMap OutputToSource;
+
+  void UpdateOutputToSourceMap(std::vector<std::string> const& outputs,
+                               cmSourceFile* source);
+  void UpdateOutputToSourceMap(std::string const& output,
+                               cmSourceFile* source);
 };
 
 //----------------------------------------------------------------------------