[LLVMdev] Ideas for making llvm-config --cxxflags more useful
mehdi.amini at apple.com
Mon Aug 3 10:30:17 PDT 2015
> On Aug 3, 2015, at 10:24 AM, Chris Bieneman <beanz at apple.com> wrote:
> Hey Tom,
> I’m not a regular user of llvm-config, but this sounds completely right to me, and it would be a significant improvement over what we have now.
> The only question I want to raise is, what about NDEBUG? There are headers that conditionalize on NDEBUG, which could lead to ABI incompatibility in the C++ API.
Is it something that can be fixed or would it be too complicated to handle?
It would be nice in general to be able to link a “Non assert” build of Clang with an “Assert" version of LLVM (and vice-versa).
And on the original topic: +1 for Tom proposal/goal, it makes sense to me.
> Thanks for doing this,
>> On Jul 30, 2015, at 1:04 PM, tom at stellard.net wrote:
>> My understanding of llvm-config --cxxflags is that it is supposed to report
>> which flags are necessary to compile a program that will include LLVM's
>> headers and link against its libraries. What it currently reports is
>> all of the flags which were used to compile LLVM. This is not very useful,
>> because users are required in most cases to filter out flags they don't
>> I would like to try to fix this so that it reports only the bare minimum
>> of required flags. As an example here all the flags that it reports in
>> my autoconf build of llvm:
>> Of these flags the only ones that are really required are (c++ experts
>> please correct me if I'm wrong here):
>> Technically the -D__STDC* macros are only required if you include
>> Support/DataTypes.h, but I think that is hard to avoid.
>> As I understand, The rest of the flags are not required in 100% of the
>> use cases.
>> My proposal for fixing this is to remove everything but the 5 options listed
>> For flags like -fno-rtti (are there others?) that are required in some cases
>> (I think -fno-rtti is required only if you sub-class LLVM objects), I would propose
>> adding a separate flag like --uses-rtti. This would give users more fine-grained
>> control over which flags they use, and also would let them choose the correct
>> flag since, for example, -fno-rtti is not understood by MSVC.
>> How do people feel about this proposal?
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