[Tarantool-patches] [PATCH] cmake: add LTO support for building luajit

Olga Arkhangelskaia arkholga at tarantool.org
Wed Apr 15 16:22:20 MSK 2020


Hi Igor!

See diff below:

14.04.2020 20:00, Igor Munkin пишет:
> Olya,
>
> Thanks for the fixes! There are still a couple nits below.
>
> On 14.04.20, Olga Arkhangelskaia wrote:
>> Hi once again!
>>
>> I have fixed your comments and pushed once again. See below.
>>
>> 14.04.2020 12:18, Igor Munkin пишет:
>>> Olya,
>>>
>>> Thanks for the patch! I left several comments below, please consider
>>> them.
>>>
>>> On 12.03.20, Olga Arkhangelskaia wrote:
>>>> Tarantool has LTO support, however while building luajit this opt. was
>>>> omitted. Patch adds necessary flag to turn it on.
>>>>
>>>> Minimum compiler/linker versions: clang 3.4, gcc 5.0+, ld 2.27+.
>>>>
>>>> Closes #3743
>>>> ---
>>>> Branch: OKriw/gh-3743-LuaJIT-does-not-use-LTO-with-DENABLE_LTO=ON-full-ci
>>>>    cmake/lto.cmake    |  3 ++-
>>>>    cmake/luajit.cmake | 26 ++++++++++++++++++++++++++
>>>>    2 files changed, 28 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/cmake/lto.cmake b/cmake/lto.cmake
>>>> index 95ade75f4..9f29f3324 100644
>>>> --- a/cmake/lto.cmake
>>>> +++ b/cmake/lto.cmake
>>>> @@ -78,7 +78,8 @@ if (NOT TARGET_OS_DARWIN)
>>>>            if (linker_version VERSION_LESS "2.31")
>>>>                message(FATAL_ERROR "ld.bfd >= 2.31 is needed for LTO")
>>>>            endif()
>>>> -    elseif(matched_gold)
>>>> +
>>>> +	elseif(matched_gold)
>>> Typo: there is a mess with whitespace above.
>>>
>>> However this chunk provides no changes except whitespace and newline.
>>> Please drop it.
>>>
>> Tarantool has LTO support, however while building luajit this opt. was
>> omitted. Patch adds necessary flag to turn it on.
>>
>> Minimum compiler/linker versions: clang 3.4, gcc 5.0+, ld 2.27+.
>>
>> Closes #3743
>> ---
>>    cmake/luajit.cmake | 23 +++++++++++++++++++++++
>>    1 file changed, 23 insertions(+)
>>
>>
>>>>            set(linker_version ${CMAKE_MATCH_1})
>>>>            message(STATUS "Found ld.gold version: ${linker_version}")
>>>>    
>>>> diff --git a/cmake/luajit.cmake b/cmake/luajit.cmake
>>>> index 072db8269..da1b4926d 100644
>>>> --- a/cmake/luajit.cmake
>>>> +++ b/cmake/luajit.cmake
>>>> @@ -225,6 +225,32 @@ macro(luajit_build)
>>>>            set(luajit_xcflags ${luajit_xcflags} -D${def})
>>>>        endforeach()
>>>>    
>>>> +    # Add LTO option to luajit
>>>> +    if (CMAKE_INTERPROCEDURAL_OPTIMIZATION)
>>>> +	    message("Setting LTO flags for building luajit")
>>>> +	# Clang opt to support LTO
>>>> +	if (CMAKE_COMPILER_IS_CLANG AND
>>>> +	    NOT ${CMAKE_CXX_COMPILER_VERSION} VERSION_LESS 3.4)
>>> So, if clang toolchain is used but version is less than 3.4, then gcc
>>> toolchain settings are used. It's either totally wrong or definitely
>>> need to be clarified with a corresponding comment.
>>>
>>> Also, AFAICS LTO support for toolchain is checked via CheckIPOSupported
>>> CMake module. So additional check here looks to be excess or also need
>>> to be clarified.
>>>
>>>> +	    if (${CMAKE_CXX_COMPILER_VERSION} VERSION_LESS 3.9)
>>>> +		set(luajit_cflags ${luajit_cflags} -flto=full)
>>>> +	    else()
>>>> +	        set(luajit_cflags ${luajit_cflags} -flto=full)
>>>> +	    endif()
>>> I see no difference in the branches above.
>>>
>>>> +	if (NOT TARGET_OS_DARWIN)
>>>> +	   # Depending of compiler we need to set appropriate llvm/gcc-ar lib
>>>> +	   set (CMAKE_AR llvm-ar)
>>> What ar is used on systems different from Darwin based ones when clang
>>> toolchain is used?
>>>
>>>> +	endif()
>>>> +	# GNU opts to support lto
>>>> +	else()
>>>> +	   #Due to some problems (bugs, slow work, etc) we support LTO only for 5.0+
>>>> +	   #The same is for binutils prior 2.27
>>>> +	   if (NOT ${CMAKE_CXX_COMPILER_VERSION} VERSION_LESS 5.0
>>>> +	       AND NOT ${linker_version} VERSION_LESS 2.27)
>>>> +	       set(luajit_cflags ${luajit_cflags} -flto -fuse-linker-plugin -fno-fat-lto-objects)
>>>> +	   endif()
>>>> +	   set (CMAKE_AR gcc-ar)
>>> Could you please clarify why ar is set explicitly here?
>>>
>>>> +        endif()
>>>> +    endif()
>> +    # Add LTO option to luajit
>> +    if (CMAKE_INTERPROCEDURAL_OPTIMIZATION)
>> +           message("Setting LTO flags for building luajit")
>> +       # Clang opt to support LTO
>> +       if (CMAKE_COMPILER_IS_CLANG)
>> +           if (${CMAKE_CXX_COMPILER_VERSION} VERSION_LESS 3.9)
>> +               set(luajit_cflags ${luajit_cflags} -flto=full)
>> + else()
>> +               set(luajit_cflags ${luajit_cflags} -flto=thin)
>> + endif()
> Moved our discussion below:
>
> ================================================================================
>
>>> I see no difference in the branches above.
>> I have a mistake here (Thin LTO) - will wix it
>>
>> If version is above than 3.9 we can use -flto=thin
> What is the difference between "full" and "thin" values? Please drop a
> few words regarding it.
>
> ================================================================================
>
>> +          # Depending of compiler we need to set appropriate
>> llvm/gcc-ar lib
>> +          set (CMAKE_AR llvm-ar)
> Moved our discussion below:
>
> ================================================================================
>
>>> What ar is used on systems different from Darwin based ones when clang
>>> toolchain is used?
>>
>> gcc-ar/ llvm-ar  is wrapper on ar that simply passes —plugin option. We
>> need it for LTO.
>>
>> ( See https://bugzilla.redhat.com/show_bug.cgi?id=1678826
>>
>> https://lists.llvm.org/pipermail/llvm-dev/2018-March/122018.html)
>> <https://lists.llvm.org/pipermail/llvm-dev/2018-March/122018.html>
> It would be nice to leave a comment regarding it.
>
> ================================================================================
>
>> +       # GNU opts to support lto
> Minor: Please move this comment under <else()> statement as the
> corresponding clang-related comment.
>
>> + else()
>> +          #Due to some problems (bugs, slow work, etc) we support LTO
>> only for 5.0+
>> +          #The same is for binutils prior 2.27
> Typo: Please separate # from the comment with a space.
>
>> +          if (NOT ${CMAKE_CXX_COMPILER_VERSION} VERSION_LESS 5.0
>> +              AND NOT ${linker_version} VERSION_LESS 2.27)
> Are there any versions supporting LTO/IPO less than gcc-5.0 and ld-2.27?
> If yes, please mention why they don't fit our purposes. If not, I see no
> rationale for this condition.
>
>> +              set(luajit_cflags ${luajit_cflags} -flto
>> -fuse-linker-plugin -fno-fat-lto-objects)
>> + endif()
>> +          set (CMAKE_AR gcc-ar)
> Minor: there are some <set> commands with a whitespace prior to
> parentheses and some without. Please adjust those you introduced within
> your changes to a single style.
>
>> + endif()
>> +    endif()
>>> Typo: there is a mess with indent above. Unfortunately I failed to find
>>> our CMake style guide, so please adjust your changes considering the
>>> code nearby.
>>>
>>>>        # Pass the same toolchain that is used for building of
>>>>        # tarantool itself, because tools from different toolchains
>>>>        # can be incompatible. A compiler and a linker are already set
>>>> -- 
>>>> 2.20.1 (Apple Git-117)
>>>>

            if (${CMAKE_CXX_COMPILER_VERSION} VERSION_LESS 3.9)

-                set(luajit_cflags ${luajit_cflags} -flto=full)
+                set (luajit_cflags ${luajit_cflags} -flto=full)
              else()
-                set(luajit_cflags ${luajit_cflags} -flto=thin)
+               # ThinLTO that is both scalable and incremental
+               # due to parallel IPO, available since 3.9 and above.
+               # See 
http://blog.llvm.org/2016/06/thinlto-scalable-and-incremental-lto.html
+               set (luajit_cflags ${luajit_cflags} -flto=thin)
              endif()
              # Depending of compiler we need to set appropriate 
llvm/gcc-ar lib
              # llvm/gcc -ar is just a wrapper over ar to pass --plugin= 
option,
              # so that ar can understand LTO objects.
-            set (CMAKE_AR llvm-ar)
-        # GNU opts to support lto
+            # See 
https://lists.llvm.org/pipermail/llvm-dev/2018-March/122018.html
+           set (CMAKE_AR llvm-ar)
          else()
-        # Due to some problems (bugs, slow work, etc) we support LTO 
only for 5.0+
-        # The same is for binutils prior 2.27
+       # GNU opts to support lto
+               # Due to some problems (bugs, slow work, etc) we support 
LTO only for 5.0+
+               # The same is for binutils prior 2.27
+               # See https://patchwork.kernel.org/patch/10078207/
              if (NOT ${CMAKE_CXX_COMPILER_VERSION} VERSION_LESS 5.0
                  AND NOT ${linker_version} VERSION_LESS 2.27)
-                set(luajit_cflags ${luajit_cflags} -flto 
-fuse-linker-plugin -fno-fat-lto-objects)
+                set (luajit_cflags ${luajit_cflags} -flto 
-fuse-linker-plugin -fno-fat-lto-objects)
              endif()
+           # The same as for llvm-ar
+           # See, https://bugzilla.redhat.com/show_bug.cgi?id=1678826



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