Re: [PATCH] Basic asm blocks should always be volatile

[Andrew Pinski <pinskia@gmail.com>]

On Wed, Jun 28, 2023 at 8:04 AM Michael Matz <matz@suse.de> wrote:
>
> Hello,
>
> On Wed, 28 Jun 2023, Julian Waters via Gcc wrote:
>
> > On the contrary, code compiled with gcc with or without the applied patch
> > operates very differently, with only gcc with the applied patch producing a
> > fully correctly operating program as expected. Even if the above inline
> > assembly blocks never worked due to other optimizations however, the
> > failure mode of the program would be very different from how it fails now:
> > It should fail noisily with an access violation exception due to
> > the malformed assembly, but instead all the assembly which installs an
> > exception handler never makes it into the final program because with
> > anything higher than -O1 gcc deletes all of it (I have verified this with
> > objdump too),
>
> Can you please provide a _full_ compilable testcase (preprocessed).  What
> Andrew says is (supposed to be) correct: ignoring the other
> problems you're going to see with your asms (even if you make them
> volatile) GCC should not remove any of the asm statements of them.
>
> If something changes when you add 'volatile' by hand then we have another
> problem lurking somewhere, and adding the parser patch might not fully
> solve it (even if it changes behaviour for you).

By the way I just testcase:
```
void f(void)
{
  asm("#should be volatile");
}
```

The produced gimple (via -fdump-tree-gimple=/dev/stdout) is:
```
void f ()
{
  __asm__ __volatile__("#should be volatile");
}
```

Which is 100% volatile. and I tested all the way back to GCC 4.8.0 and
it was volatile back then too.
So as both Michael and myself have mentioned, we need a full
(compilable) testcase, even if it is for mingw or cygwin, we can
handle those just fine too.

Thanks,
Andrew

>
>
> Ciao,
> Michael.