[PATCH] D16999: [CMake] Improve the clang order-file generation workflow

[Chris Bieneman via cfe-commits]

beanz created this revision.
beanz added a reviewer: bogner.
beanz added a subscriber: cfe-commits.

This commit re-lands r259862. The underlying cause of the build breakage was an incorrectly written capabilities test. In tools/Driver/CMakeLists.txt I was attempting to check if a linker flag worked, the test was passing it to the compiler, not the linker. CMake doesn't have a linker test, so we have a hand-rolled one.

Original Patch Review: http://reviews.llvm.org/D16896

Original Summary:
With this change generating clang order files using dtrace uses the following workflow:

cmake <whatever options you want>

ninja generate-order-file

ninja clang

This patch works by setting a default path to the order file (which can be overridden by the user). If the order file doesn't exist during configuration CMake will create an empty one.

CMake then ties up the dependencies between the clang link job and the order file, and generate-order-file overwrites CLANG_ORDER_FILE with the new order file.

http://reviews.llvm.org/D16999

Files:
  CMakeLists.txt
  tools/driver/CMakeLists.txt
  utils/perf-training/CMakeLists.txt

Index: utils/perf-training/CMakeLists.txt
===================================================================
--- utils/perf-training/CMakeLists.txt
+++ utils/perf-training/CMakeLists.txt
@@ -55,9 +55,8 @@
     COMMAND ${PYTHON_EXECUTABLE} ${CMAKE_CURRENT_SOURCE_DIR}/perf-helper.py clean ${CMAKE_CURRENT_BINARY_DIR} dtrace
     COMMENT "Clearing old dtrace data")
 
-
   add_custom_target(generate-order-file
-    COMMAND ${PYTHON_EXECUTABLE} ${CMAKE_CURRENT_SOURCE_DIR}/perf-helper.py gen-order-file --binary $<TARGET_FILE:clang> --output ${CMAKE_CURRENT_BINARY_DIR}/clang.order ${CMAKE_CURRENT_BINARY_DIR}
+    COMMAND ${PYTHON_EXECUTABLE} ${CMAKE_CURRENT_SOURCE_DIR}/perf-helper.py gen-order-file --binary $<TARGET_FILE:clang> --output ${CLANG_ORDER_FILE} ${CMAKE_CURRENT_BINARY_DIR}
     COMMENT "Generating order file"
     DEPENDS generate-dtrace-logs)
 endif()
Index: tools/driver/CMakeLists.txt
===================================================================
--- tools/driver/CMakeLists.txt
+++ tools/driver/CMakeLists.txt
@@ -87,8 +87,24 @@
   set(TOOL_INFO_BUILD_VERSION)
 endif()
 
-if(CLANG_ORDER_FILE AND EXISTS CLANG_ORDER_FILE)
-  target_link_libraries(clang "-Wl,-order_file,${CLANG_ORDER_FILE}")
+if(CLANG_ORDER_FILE)
+  include(CMakePushCheckState)
+
+  function(check_linker_flag flag out_var)
+    cmake_push_check_state()
+    set(CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS} ${flag}")
+    check_cxx_compiler_flag("" ${out_var})
+    cmake_pop_check_state()
+  endfunction()
+
+  # This is a test to ensure the actual order file works with the linker.
+  check_linker_flag("-Wl,-order_file,${CLANG_ORDER_FILE}"
+    LINKER_ORDER_FILE_WORKS)
+  
+  if(LINKER_ORDER_FILE_WORKS)
+    target_link_libraries(clang "-Wl,-order_file,${CLANG_ORDER_FILE}")
+    set_target_properties(clang PROPERTIES LINK_DEPENDS ${CLANG_ORDER_FILE})
+  endif()
 endif()
 
 if(WITH_POLLY AND LINK_POLLY_INTO_TOOLS)
Index: CMakeLists.txt
===================================================================
--- CMakeLists.txt
+++ CMakeLists.txt
@@ -586,18 +586,19 @@
   add_subdirectory(docs)
 endif()
 
-if(EXISTS "${CMAKE_CURRENT_BINARY_DIR}/clang.order")
-  file(REMOVE "${CMAKE_CURRENT_BINARY_DIR}/clang.order")
-endif()
-
-if(CLANG_ORDER_FILE STREQUAL "${CMAKE_CURRENT_BINARY_DIR}/clang.order")
+# this line is needed as a cleanup to ensure that any CMakeCaches with the old
+# default value get updated to the new default.
+if(CLANG_ORDER_FILE STREQUAL "")
   unset(CLANG_ORDER_FILE CACHE)
-  unset(CLANG_ORDER_FILE)
 endif()
 
-set(CLANG_ORDER_FILE "" CACHE FILEPATH
+set(CLANG_ORDER_FILE ${CMAKE_CURRENT_BINARY_DIR}/clang.order CACHE FILEPATH
   "Order file to use when compiling clang in order to improve startup time.")
 
+if(CLANG_ORDER_FILE AND NOT EXISTS ${CLANG_ORDER_FILE})
+  file(WRITE ${CLANG_ORDER_FILE} "\n")
+endif()
+
 if (CLANG_BUILT_STANDALONE OR CMAKE_VERSION VERSION_EQUAL 3 OR
     CMAKE_VERSION VERSION_GREATER 3)
   # Generate a list of CMake library targets so that other CMake projects can


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