[LLVMdev] Ideas for making llvm-config --cxxflags more useful
beanz at apple.com
Mon Aug 3 10:24:29 PDT 2015
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.
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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