Re: ifcvt.c and STORE_FLAG_VALUE

["Philippe De Muyter" <phdm at macqel dot be>]

John Vickers wrote :
> Philippe De Muyter wrote:
> > 
> > Bootstrapping on m68k-motorola-sysv yields also the following failure:
> > 
> > cc -c  -DIN_GCC    -g   -DHAVE_CONFIG_H    -I. -I/gcc -I/gcc/config -I/gcc/../include /gcc/ifcvt.c
> > "/gcc/ifcvt.c", line 519: illegal lhs of assignment operator
> > "/gcc/ifcvt.c", line 557: illegal lhs of assignment operator
> > "/gcc/ifcvt.c", line 640: illegal lhs of assignment operator
> > 
> > That happens with -STORE_FLAG_VALUE when STORE_FLAG_VALUE is defined as -1
> 
> > I thought to define it as (-1), but as it it tested in preprocessor
> > expressions for equality with -1, I did not dare to do that.
> 
> Sorry if I'm being dense, but the brackets in the macro definition
> don't look like a courageous step to me.
> 
> Presumably you agree that normally we should have the brackets
> in the definition, rather than hacking the point of use, but you
> perhaps know of a preprocessor where this would break ?

The preprocessor I tested on afterwards does not break, but all the
documentation says STORE_FLAG_VALUE has a value of 1 or -1, not (-1).

And I have found other places where protecting STORE_FLAG_VALUE from - was
done that way, or with a space between - and STORE_FLAG_VALUE.

./gcc/combine.c:                   && INTVAL (true) == - STORE_FLAG_VALUE
./gcc/combine.c:                   && INTVAL (false) == - STORE_FLAG_VALUE
./gcc/expmed.c:   else if (- normalizep == STORE_FLAG_VALUE)

So, for the moment I feel inclined to only add a space between - and
STORE_FLAG_VALUE, instead of my proposed fix, but I will fix every definition
of STORE_FLAG_VALUE and the documentation if that's what the majority wants.

> 
> Regards,
> 
> John.
> 
> >  My proposed fix
> > is below.  OK to commit ?
> > 
> > Philippe De Muyter  <phdm@macqel.be>
> > 
> >         * ifcvt.c (noce_try_store_flag_constants): Do not negate
> >         STORE_FLAG_VALUE.
> [...]
> > -      if (diff == STORE_FLAG_VALUE || diff == -STORE_FLAG_VALUE)
> > +      if (diff == STORE_FLAG_VALUE || -diff == STORE_FLAG_VALUE)
> 
> Michael Meissner wrote:
> > 
> > Yes it is ok to commit, providing you put in a comment of why this is being
> > done, or possibly change the line to:
> > 
> >         if (diff == STORE_FLAG_VALUE || diff == -(STORE_FLAG_VALUE))
>