Re: working around "QImode can alias everything" missed optimizations

[Mike Stump <mrs at windriver dot com>]

> From: Doug Evans <dje@transmeta.com>
> Date: Mon, 29 May 2000 02:06:38 -0700 (PDT)
> To: Richard Henderson <rth@cygnus.com>
> Cc: gcc@gcc.gnu.org

> Richard Henderson writes:
>  > On Fri, May 26, 2000 at 03:43:55PM -0700, Doug Evans wrote:
>  > > (I'm guessing because it can't know that buf may point to itself
>  > > and QImode values are allowed to alias anything).
>  > 
>  > Yep.
>  > 
>  > > So how do I work around this?
>  > 
>  > You can't.  :-(

> I was afraid you were going to say that.

> Any interest in fixing this [dunno how yet]?  GCC produces great
> code for non-QImode values (well done!).  It has to be agreed that
> QImode values shouldn't be penalized (right?).  [not that I would
> change behaviour of course, but rather that some new way of
> specifying a "ya, I'm a QImode (ptr) value but, gosh darn it, I
> don't alias everything" value needs to be found.  Alternatively, one
> might come up with another way, but this way seems at first glance
> like the right way to go.

The standard already has this.  It is called int8_t.  It is not a
character type, and the alias stuff makes an exception only for
character type (s/u/plain char).  So there you have it.  We just need
to fix an brokenness in the compiler that doesn't respect this fact.