[cfe-dev] Language not recognized: 'c++-module-cpp-output'

[Richard Smith via cfe-dev]

On 3 Jun 2017 7:07 am, "Boris Kolpackov" <boris at codesynthesis.com> wrote:

Richard Smith <richard at metafoo.co.uk> writes:

> What difference are you expecting the -cpp-output to make to the
> compilation?

Make it a lot faster? ;-)


I think you misunderstood my question. What difference do you expect the -x
c++-cpp-output / -x c++-module-cpp-output flag to make, compared to passing
-x c++ / -x c++-module for the same input file? What do you think that flag
does?

Seriously, though, in my case I know that certain TU do not use the
preprocessor. I do some optimizations at the build system level but
also want to pass this information along to the compiler in case it
wants to do some as well. It may not do any currently (e.g., because
such preprocessed TU are virtually non-existent and its not worth the
effort). But maybe it makes sense to "reserve" the name even if it's
just an alias for 'c++-module'. But I am also happy to always pass
'c++-module' (and perhaps 'c++' for consistency).

Also, on the topic of expectations: I assume that such a preprocessed
TU can still contain comments and line continuations. Clang's -cpp-output
handles this but not GCC's (where I use -fdirectives-only to indicate
that the source is only partially preprocessed).

Boris
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