[llvm-commits] [llvm] r117102 - /llvm/trunk/cmake/modules/TableGen.cmake

[Oscar Fuentes]

Author: ofv
Date: Fri Oct 22 11:20:10 2010
New Revision: 117102

URL: http://llvm.org/viewvc/llvm-project?rev=117102&view=rev
Log:
Teach CMake to only touch tablegen-generated files if anything
actually changed.

Patch by Frits van Bommel!

Modified:
    llvm/trunk/cmake/modules/TableGen.cmake

Modified: llvm/trunk/cmake/modules/TableGen.cmake
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/cmake/modules/TableGen.cmake?rev=117102&r1=117101&r2=117102&view=diff
==============================================================================
--- llvm/trunk/cmake/modules/TableGen.cmake (original)
+++ llvm/trunk/cmake/modules/TableGen.cmake Fri Oct 22 11:20:10 2010
@@ -13,10 +13,19 @@
       ${CMAKE_CURRENT_SOURCE_DIR}/${LLVM_TARGET_DEFINITIONS})
   endif()
   add_custom_command(OUTPUT ${CMAKE_CURRENT_BINARY_DIR}/${ofn}
+    # Generate tablegen output in a temporary file.
     COMMAND ${LLVM_TABLEGEN_EXE} ${ARGN} -I ${CMAKE_CURRENT_SOURCE_DIR}
     -I ${LLVM_MAIN_SRC_DIR}/lib/Target -I ${LLVM_MAIN_INCLUDE_DIR}
     ${LLVM_TARGET_DEFINITIONS_ABSOLUTE} 
-    -o ${CMAKE_CURRENT_BINARY_DIR}/${ofn}
+    -o ${CMAKE_CURRENT_BINARY_DIR}/${ofn}.tmp
+    # Only update the real output file if there are any differences.
+    # This prevents recompilation of all the files depending on it if there
+    # aren't any.
+    COMMAND ${CMAKE_COMMAND} -E copy_if_different
+        ${CMAKE_CURRENT_BINARY_DIR}/${ofn}.tmp
+        ${CMAKE_CURRENT_BINARY_DIR}/${ofn}
+    # Either way, we no longer need the temporary file.
+    COMMAND ${CMAKE_COMMAND} -E remove ${CMAKE_CURRENT_BINARY_DIR}/${ofn}.tmp
     DEPENDS tblgen ${local_tds} ${global_tds}
     COMMENT "Building ${ofn}..."
     )