[llvm] r222308 - Teach llvm-build to avoid touching LibraryDependencies.inc unless the contents

[Peter Collingbourne]

Author: pcc
Date: Tue Nov 18 21:34:20 2014
New Revision: 222308

URL: http://llvm.org/viewvc/llvm-project?rev=222308&view=rev
Log:
Teach llvm-build to avoid touching LibraryDependencies.inc unless the contents
change. This saves us from rebuilding llvm-config each time we reconfigure.

Modified:
    llvm/trunk/utils/llvm-build/llvmbuild/main.py

Modified: llvm/trunk/utils/llvm-build/llvmbuild/main.py
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/utils/llvm-build/llvmbuild/main.py?rev=222308&r1=222307&r2=222308&view=diff
==============================================================================
--- llvm/trunk/utils/llvm-build/llvmbuild/main.py (original)
+++ llvm/trunk/utils/llvm-build/llvmbuild/main.py Tue Nov 18 21:34:20 2014
@@ -1,4 +1,5 @@
 from __future__ import absolute_import
+import filecmp
 import os
 import sys
 
@@ -382,7 +383,7 @@ subdirectories = %s
 
         # Write out the library table.
         make_install_dir(os.path.dirname(output_path))
-        f = open(output_path, 'w')
+        f = open(output_path+'.new', 'w')
         f.write("""\
 //===- llvm-build generated file --------------------------------*- C++ -*-===//
 //
@@ -420,6 +421,14 @@ subdirectories = %s
         f.write('};\n')
         f.close()
 
+        if not os.path.isfile(output_path):
+            os.rename(output_path+'.new', output_path)
+        elif filecmp.cmp(output_path, output_path+'.new'):
+            os.remove(output_path+'.new')
+        else:
+            os.remove(output_path)
+            os.rename(output_path+'.new', output_path)
+
     def get_required_libraries_for_component(self, ci, traverse_groups = False):
         """
         get_required_libraries_for_component(component_info) -> iter