dblaikie added a comment.
>> (I'd still sort of lean towards "make it the same as the .o, but with the
>> .pcm suffix" and if the build system wants to put things in other places, it
>> can move them around - but I understand why that's not something everyone's
>> on board with)
>
> Actually, I would think that to be a great default (and put it in the CWD
> just like the object),
> .. but it seems (in addition to the default) we do need a way to place
> specific module files - and I could imagine needing to make different places
> for different command line option sets. Asking the driver or build system to
> move the file seems like spawning more processes and we'd still need a
> user-visible way to say where we wanted the file to be put.
At least I'd like these to be separate patches - adding ".cppm -> {.pcm + .o}"
action and then separately adding a way to specify the name of the .pcm output
file.
But I still have some reservations about even providing a flag for it - I think
the example I was thinking of was coverage files (
https://gcc.gnu.org/onlinedocs/gcc/Gcov-Data-Files.html ) which also don't have
a custom path option, like Split DWARF. I'd be happy not to add this until
someone comes back with a demonstrated need - it doesn't seem like it'd be a
major imposition on a build system to copy the file if it needed to to move it
into a release tree V the build tree, for instance. And if it did add up to
real performance problems, we could add it.
>> Yeah, if the `-fmodule-file` syntax is currently only for input I don't
>> think we need to try to overload it for output as well.
>
> My understanding [which could be flawed] is that the second syntax (which
> already exists, it's not an invention of this discussion) is intended to
> allow specification of output files.
I haven't seen evidence of that, but it's certainly not something I've got lots
of info on. It looks like it was added in https://reviews.llvm.org/D35020 as a
search path.
I think the first patch (be it using this review or another) should be just the
".cppm -> {.pcm + .o}" (which should basically be entirely in the driver,
right? Since for now it'll still be two actions that are already implemented)
and then another for "here's a flag to name the .pcm output file" (not sure if
we need that, really, just yet) and possibly another for "here's an option to
write the .pcm file out to a cache directory instead of the .o path or custom
.pcm output path" (I've even stronger reservations about that). I guess
discussing the second and third somewhat together, if their flag interface
might interact (since they both specify where the .pcm file goes).
CHANGES SINCE LAST ACTION
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https://reviews.llvm.org/D134267
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