Teach CMake to only touch tablegen-generated files if anything
actually changed.
Patch by Frits van Bommel!
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@117102 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/cmake/modules/TableGen.cmake b/cmake/modules/TableGen.cmake
index cf7cd1f..bb8fc13 100644
--- a/cmake/modules/TableGen.cmake
+++ b/cmake/modules/TableGen.cmake
@@ -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}..."
)