[cfe-dev] [Modules TS] feedback

[David Blaikie via cfe-dev]

On Thu, May 11, 2017 at 6:22 AM Boris Kolpackov <boris at codesynthesis.com>
wrote:

> Hi David,
>
> David Blaikie <dblaikie at gmail.com> writes:
>
> > Passing -fmodules-codegen and -fmodules-debuginfo (I think I'm
> remembering
> > the spelling right) to the step that creates the pcm file will establish
> > the right conditions, then passing that pcm file to clang again -c,
> should
> > generate the required object file.
>
> While I believe the spelling is correct, it still does not work:
>
> clang++-5.0 -std=c++1z -fmodules-ts -fmodules-codegen -fmodules-debuginfo \
>   -I.. --precompile -x c++-module -o hello.pcm hello.mxx
>
> clang: error: unknown argument: '-fmodules-codegen'
> clang: error: unknown argument: '-fmodules-debuginfo'
>

Right, sorry - these flags aren't exposed through the driver yet, so for
now you can pass them like:

  -Xclang -fmodules-codegen
  -Xclang -fmodules-debuginfo


>
> Also note that this is not an unresolved symbol but a duplicate:
>

It should work naturally either way, I think.

Here we go:

  foo.cppm:
    export module foo;
    export {
      int f() { return 0; }
    }
  use1.cpp:
    import foo;
    void use1() { f(); }
  use2.cpp:
    import foo;
    void use1();
    int main() { f(); use1(); }

  $ clang++-tot -std=c++1z -fmodules-ts foo.cppm --precompile -o foo.pcm
-Xclang -fmodules-codegen
  $ clang++-tot -std=c++1z -fmodules-ts foo.pcm -c
  $ clang++-tot -std=c++1z -fmodules-ts -fmodule-file=foo.pcm use1.cpp
use2.cpp -c
  $ nm {foo,use1,use2}.o
  foo.o:
  0000000000000000 T _Z1fv
  use1.o:
  0000000000000000 T main
                   U _Z1fv
                   U _Z4use2v
  use2.o:
                   U _Z1fv
  0000000000000000 T _Z4use2v
  $ clang++-tot {foo,use1,use2}.o
  $ ./a.out
  $ clang++-tot -std=c++1z -fmodules-ts foo.cppm --precompile -o foo.pcm
  $ clang++-tot -std=c++1z -fmodules-ts -fmodule-file=foo.pcm use1.cpp
use2.cpp -c
  $ nm {use1,use2}.o
  use1.o:
  0000000000000010 T main
  0000000000000000 T _Z1fv
                   U _Z4use2v
  use2.o:
  0000000000000000 T _Z1fv
  0000000000000010 T _Z4use2v
  $ clang++-tot use1.o use2.o
  use2.o: In function `f()':
  use2.cpp:(.text+0x0): multiple definition of `f()'
  use1.o:use1.cpp:(.text+0x0): first defined here

I suppose -fmodules-codegen will be the default for -fmodules-ts sooner or
later. (-fmodules-debuginfo is useful too, but you won't see the
correctness issue, just debug info size changes)

It may be that two degrees of -fmodules-codegen would be useful - one that
only homes the non-inline functions (external functions become external in
the module's object, available_externally in module users objects), and the
one we have here that homes all functions (even inline ones, so
linkonce_odr functions become weak in the module's object and
available_externally in module users objects).


> clang++-5.0 -std=c++1z -fmodules-ts -I.. --precompile -x c++-module -o
> hello.pcm hello.mxx
> clang++-5.0 -std=c++1z -fmodules-ts -I.. -fmodule-file=hello.pcm -c
> hello.cxx
> clang++-5.0 -std=c++1z -fmodules-ts -I.. -fprebuilt-module-path=. -c
> driver.cxx
> clang++-5.0 -std=c++1z -fmodules-ts -I.. -o driver driver.o hello.o
> hello.o: In function `hello::non_inline()':
> hello.cxx:(.text+0x0): multiple definition of `hello::non_inline()'
> driver.o:driver.cxx:(.text+0x0): first defined here
>
> Thanks,
> Boris
>
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