Add a section-ordering script

I think this lets us specify that certain functions should be
put together at the end of the text segment.

This is inspired by a similar feature of HHVM's build, though the goal
for us for now is just to improve performance consistency rather
than overall performance.  Hopefully soon/eventually we can do
profile-guided sorting like they do.

Some of the performance changes here are very dramatic and I can't
explain them.  No wonder performance debugging is hard when link
ordering could easily produce +-20% changes.

Author: kmod

CMakeLists.txt

@@ -45,9 +45,11 @@ if(ENABLE_GOLD)
     message(STATUS "found the gold linker ${GOLD_LINKER}")
     set(CMAKE_LINKER "${GOLD_LINKER}")
     set(CMAKE_CXX_LINK_FLAGS "${CMAKE_CXX_LINK_FLAGS} -B${CMAKE_SOURCE_DIR}/tools/build_system")
+    set(CMAKE_CXX_LINK_FLAGS "${CMAKE_CXX_LINK_FLAGS} -Wl,--section-ordering-file,${CMAKE_CURRENT_SOURCE_DIR}/section_ordering.txt")
   endif()
 endif()
 
+
 # pyston self host mode
 if(ENABLE_SELF_HOST)
   set(PYTHON_EXE "pyston")
@@ -196,7 +198,11 @@ add_subdirectory(test/test_extension)
 add_subdirectory(test/unittests)
 add_subdirectory(tools)
 
-add_executable(pyston $<TARGET_OBJECTS:PYSTON_MAIN_OBJECT> $<TARGET_OBJECTS:PYSTON_OBJECTS> $<TARGET_OBJECTS:FROM_CPYTHON>)
+# There are supposed to be better ways [1] to add link dependencies, but none of them worked for me.
+# [1] http://www.cmake.org/pipermail/cmake/2010-May/037206.html
+add_custom_command(OUTPUT ${CMAKE_BINARY_DIR}/linkdeps_dummy.c COMMAND ${CMAKE_COMMAND} -E touch ${CMAKE_BINARY_DIR}/linkdeps_dummy.c DEPENDS ${CMAKE_SOURCE_DIR}/section_ordering.txt)
+
+add_executable(pyston $<TARGET_OBJECTS:PYSTON_MAIN_OBJECT> $<TARGET_OBJECTS:PYSTON_OBJECTS> $<TARGET_OBJECTS:FROM_CPYTHON> linkdeps_dummy.c)
 # Wrap the stdlib in --whole-archive to force all the symbols to be included and eventually exported
 target_link_libraries(pyston -Wl,--whole-archive stdlib -Wl,--no-whole-archive pthread m readline sqlite3 gmp ssl crypto unwind pypa liblz4 double-conversion ${LLVM_LIBS} ${LIBLZMA_LIBRARIES} ${OPTIONAL_LIBRARIES})
 

section_ordering.txt

@@ -0,0 +1,5 @@
+.text.intLtInt
+.text.div_i64_i64
+.text.boxInt
+.text._ZN6pyston2gc10SmallArena6_allocEmi
+.text._ZNSt17_Function_handlerIFvPN6pyston2gc10SmallArena16ThreadBlockCacheEEZNS2_12freeUnmarkedERSt6vectorIPNS0_3BoxESaIS8_EEE3$_0E9_M_invokeERKSt9_Any_dataS4_