Re: Naming flag for specifying the output file name for Binary Module Interface files

["chuanqi.xcq" <yedeng.yd@linux.alibaba.com>]

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Hi David,
> I think Nathan might've been asking not only about what currently
happens, but what we think should happen?
Yes.
> Is that consistent with `-o`? (I assume so, but don't know - I guess
there aren't many cases where `-o` is unused (maybe `-fsyntax-only`),
so that behavior might be a bit less well specified)
`-o` wouldn't emit a warning if it is not used. (with `-fsyntax-only` for example).
Since we want to make the behavior of `-fmodule-output` to be consistent with `-o`.
I've changed the behavior in https://reviews.llvm.org/D140001.
> This seems surprising/possibly wrong to me - do we have precedent from
other flags to draw from?
I feel it makes sense since `-fmodule-output=` will provide more information than `-fmodule-output`.
So it is naturally to me that `-fmodule-output=` has higher priority.
For examples, I don't enumerate all the flags but I find the following cases in minutes:
- `-fpack-struct=` has higher priority than `-fpack-struct`.
- `-fsave-optimization-record=` has higher priority than `-fsave-optimization-record=`.
- `-ftime-report=` has higher priority than `-ftime-report`.
- `-ftime-trace=` has higher priority than `-ftime-trace`.
So I think the bahavior should be correct.
Thanks,
Chuanqi
------------------------------------------------------------------
From:David Blaikie <dblaikie@gmail.com>
Send Time:2022年12月13日(星期二) 23:56
To:chuanqi.xcq <yedeng.yd@linux.alibaba.com>
Cc:Iain Sandoe <iain@sandoe.co.uk>; GCC Development <gcc@gcc.gnu.org>; Nathan Sidwell <nathanmsidwell@gmail.com>; Jonathan Wakely <jwakely.gcc@gmail.com>; ben.boeckel <ben.boeckel@kitware.com>
Subject:Re: Naming flag for specifying the output file name for Binary Module Interface files
I think Nathan might've been asking not only about what currently
happens, but what we think should happen?
On Mon, Dec 12, 2022 at 7:11 PM chuanqi.xcq <yedeng.yd@linux.alibaba.com> wrote:
>
> Hi Nathan,
>
> > 1) Are these flags silently ignored, if no module output is to be generated? Or is some kind of diagnostic generated?
>
> Currently, clang will generate the unused-command-line-argument warning for this case:
>
> ```
> argument unused during compilation: '-fmodule-output' [-Wunused-command-line-argument]
> ```
Is that consistent with `-o`? (I assume so, but don't know - I guess
there aren't many cases where `-o` is unused (maybe `-fsyntax-only`),
so that behavior might be a bit less well specified)
> > 2) what happens if you specify both -- do you get two outputs, a diagnostic, or
> is one silently selected?
>
> If someone specify both `-fmodule-output` and `-fmodule-output=/path`,
> the `-fmodule-output=/path` will be selected always no matter what the order is.
This seems surprising/possibly wrong to me - do we have precedent from
other flags to draw from?
> And if multiple `-fmodule-output=/path` are specified, the last one will be selected.
>
> > 3) What is the behaviour if compilation fails? Does nothing happen to the file
> indicated (potentially leaving an older version there), or does the equivalent
> of 'rm -f $MODULE.pcm' happen?
>
> The module file will be deleted. The behavior is the same with `-o`.
>
> Thanks,
> Chuanqi
>
>
> ------------------------------------------------------------------
> From:Nathan Sidwell <nathan@acm.org>
> Send Time:2022年12月12日(星期一) 22:30
> To:Iain Sandoe <iain@sandoe.co.uk>; GCC Development <gcc@gcc.gnu.org>
> Cc:Nathan Sidwell <nathanmsidwell@gmail.com>; Jonathan Wakely <jwakely.gcc@gmail.com>; David Blaikie <dblaikie@gmail.com>; ben.boeckel <ben.boeckel@kitware.com>; chuanqi.xcq <yedeng.yd@linux.alibaba.com>
> Subject:Re: Naming flag for specifying the output file name for Binary Module Interface files
>
> On 12/9/22 12:33, Iain Sandoe wrote:
> > Hello all.
> >
> >> On 9 Dec 2022, at 01:58, chuanqi.xcq <yedeng.yd@linux.alibaba.com> wrote:
> >>
> >> It looks like `-fmodule-file` is better from the discussion. So let's take it. Thanks for everyone here
> >
> > So FAOD (after this discussion) Chuanqi's current patchset implements the following in clang:
> >
> > -fmodule-output
> >
> > - this causes the BMI to be saved in the CWG with the basename of the source file and a suffix of .pcm.
> >
> > -fmodule-output=<path>
> >
> > - this causes the BMI to be saved at the path specified.
> >
>
> 1) Are these flags silently ignored, if no module output is to be generated? Or
> is some kind of diagnostic generated?
>
> 2) what happens if you specify both -- do you get two outputs, a diagnostic, or
> is one silently selected?
>
> 3) What is the behaviour if compilation fails? Does nothing happen to the file
> indicated (potentially leaving an older version there), or does the equivalent
> of 'rm -f $MODULE.pcm' happen?
>
> nathan
>
> --
> Nathan Sidwell
>
>