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]
```
> 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.
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