Major optimization of C/C++ dependency scanning.

Now only the dependencies for the file where the dependencies actually may
have changed are rescanned, before that this was done for all source files
even if only one source file had changed.
This reduces e.g. on my machine the time for scanning the dependencies
of kdelibs/khtml/ when only one file (khtml_global.cpp) has changed from
around 7.5 seconds to 1.2 seconds.

The tests succeed, it does what I expected it to do on kdelibs, and Brad
also reviewed the patch, so I think it should be ok.

Alex

1 files changed, 19 insertions, 7 deletions

diff --git a/Source/cmLocalUnixMakefileGenerator3.cxx b/Source/cmLocalUnixMakefileGenerator3.cxx
index 495a05a..db22d1d 100644
--- a/Source/cmLocalUnixMakefileGenerator3.cxx
+++ b/Source/cmLocalUnixMakefileGenerator3.cxx
@@ -16,7 +16,6 @@
 =========================================================================*/
 #include "cmLocalUnixMakefileGenerator3.h"
 
-#include "cmDepends.h"
 #include "cmGeneratedFileStream.h"
 #include "cmGlobalUnixMakefileGenerator3.h"
 #include "cmMakefile.h"
@@ -1387,9 +1386,9 @@ bool cmLocalUnixMakefileGenerator3::UpdateDependencies(const char* tgtInfo,
     if(verbose)
       {
       cmOStringStream msg;
-      msg << "Dependee \"" << internalDependFile
+      msg << "Dependee \"" << dirInfoFile
           << "\" is newer than depender \""
-          << dirInfoFile << "\"." << std::endl;
+          << internalDependFile << "\"." << std::endl;
       cmSystemTools::Stdout(msg.str().c_str());
       }
     needRescanDirInfo = true;
@@ -1400,14 +1399,26 @@ bool cmLocalUnixMakefileGenerator3::UpdateDependencies(const char* tgtInfo,
   // The build.make file may have explicit dependencies for the object
   // files but these will not affect the scanning process so they need
   // not be considered.
+  std::map<std::string, cmDepends::DependencyVector> validDependencies;
   bool needRescanDependencies = false;
   if (needRescanDirInfo == false)
     {
     cmDependsC checker;
     checker.SetVerbose(verbose);
     checker.SetFileComparison(ftc);
+    // cmDependsC::Check() fills the vector validDependencies() with the
+    // dependencies for those files where they are still valid, i.e. neither
+    // the files themselves nor any files they depend on have changed.
+    // We don't do that if the CMakeDirectoryInformation.cmake file has 
+    // changed, because then potentially all dependencies have changed.
+    // This information is given later on to cmDependsC, which then only
+    // rescans the files where it did not get valid dependencies via this
+    // dependency vector. This means that in the normal case, when only 
+    // few or one file have been edited, then also only this one file is
+    // actually scanned again, instead of all files for this target.
     needRescanDependencies = !checker.Check(dependFile.c_str(),
-                                            internalDependFile.c_str());
+                                            internalDependFile.c_str(),
+                                            validDependencies);
     }
 
   if(needRescanDependInfo || needRescanDirInfo || needRescanDependencies)
@@ -1426,7 +1437,7 @@ bool cmLocalUnixMakefileGenerator3::UpdateDependencies(const char* tgtInfo,
     fprintf(stdout, "%s\n", message.c_str());
 #endif
 
-    return this->ScanDependencies(dir.c_str());
+    return this->ScanDependencies(dir.c_str(), validDependencies);
     }
   else
     {
@@ -1438,7 +1449,8 @@ bool cmLocalUnixMakefileGenerator3::UpdateDependencies(const char* tgtInfo,
 //----------------------------------------------------------------------------
 bool
 cmLocalUnixMakefileGenerator3
-::ScanDependencies(const char* targetDir)
+::ScanDependencies(const char* targetDir,
+                 std::map<std::string, cmDepends::DependencyVector>& validDeps)
 {
   // Read the directory information file.
   cmMakefile* mf = this->Makefile;
@@ -1526,7 +1538,7 @@ cmLocalUnixMakefileGenerator3
     if(lang == "C" || lang == "CXX" || lang == "RC")
       {
       // TODO: Handle RC (resource files) dependencies correctly.
-      scanner = new cmDependsC(this, targetDir, lang.c_str());
+      scanner = new cmDependsC(this, targetDir, lang.c_str(), &validDeps);
       }
 #ifdef CMAKE_BUILD_WITH_CMAKE
     else if(lang == "Fortran")