[vlc-devel] [PATCH 2/2] contrib: mfx: don't force a level optimization even on non optimized builds

[Steve Lhomme]

Le 30/03/2018 à 10:36, Martin Storsjö a écrit :
> On Fri, 30 Mar 2018, Steve Lhomme wrote:
>
>> Le 29/03/2018 à 22:01, Martin Storsjö a écrit :
>>> On Thu, 29 Mar 2018, Steve Lhomme wrote:
>>>
>>>> No other contrib need it and we use the same compiler for them.
>>>> ---
>>>> contrib/src/mfx/rules.mak | 2 +-
>>>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>>>
>>>> diff --git a/contrib/src/mfx/rules.mak b/contrib/src/mfx/rules.mak
>>>> index a5b1fdaa61..f3b1287db5 100644
>>>> --- a/contrib/src/mfx/rules.mak
>>>> +++ b/contrib/src/mfx/rules.mak
>>>> @@ -23,6 +23,6 @@ mfx: mfx-$(MFX_GITHASH).tar.xz .sum-mfx
>>>>     $(MOVE)
>>>>
>>>> .mfx: mfx
>>>> -    cd $< && $(HOSTVARS) ./configure $(HOSTCONF) 
>>>> CXXFLAGS="$(CXXFLAGS) -std=c++98 -O2"
>>>> +    cd $< && $(HOSTVARS) ./configure $(HOSTCONF) 
>>>> CXXFLAGS="$(CXXFLAGS) -std=c++98"
>>>
>>> The reason for this is, if you don't override configure's CXXFLAGS, 
>>> it will implicitly contain -O2. If you do override it, it will clear 
>>> all the defaults and you'll end up with a build with no optimization 
>>> flags whatsoever, and you need to manually add the -O2 that would 
>>> otherwise have been there.
>>
>> I think if it's placed after the env CXXFLAGS it will override 
>> whatever value was set before. It may depend on the compiler though.
>
> There's no difference between if I do "./configure CXXFLAGS=-foo" or 
> "CXXFLAGS=-foo ./configure" or "export CXXFLAGS=-foo; ./configure", 
> both of them will override things that you had in $CXXFLAGS from 
> before - this has nothing to do with the compiler.
>

I meant between "$(CXXFLAGS) -O2" and "-O2 $(CXXFLAGS)". We always do 
the former, so I assume the order matters. Otherwise some flag 
overriding may not work anyway.

>> In any case it's not a good idea to discard the env flags. For 
>> example you may lose the forced _WIN32_WINNT version and 
>> WINAPI_FAMILY when building on Windows.
>
> So yes, in that aspect, it will override whatever was set before - I 
> wasn't aware that it was commonly used in the contribs build system to 
> set CFLAGS/CXXFLAGS globally. Now I see that this is done, and the 
> default flags there include -g -O2 as well.
>
> In any case, this change isn't needed any longer since I fixed libmfx 
> to build with clang in C++11 mode and got rid of overriding the flags.
>
> // Martin
>
>
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