------- Additional Comments From kazu at cs dot umass dot edu 2005-02-01 13:46
-------
Subject: Re: [4.0 Regression] A side effect
is missed in 0 % a++.
Hi Richard,
> > + /* X % 0, return X % 0 unchanged so that we can get the
> > + proper warnings and errors. */
> > if (integer_zerop (arg1))
> > return t;
> >
> > + /* 0 % X is always zero, but be sure to preserve any side
> > + effects in X. Place this after checking for X == 0. */
> > + if (integer_zerop (arg0))
> > + return omit_one_operand (type, integer_zero_node, arg1);
>
> Not ok yet. You have to *know* that arg1 is not zero. Otherwise
> you're still potentially removing a division-by-zero.
>
> The only check you have at this level for this is integer_nonzerop.
Err, if this is the case, we have to disable the equivalent
optimization at RTL level. Even if you disable this tree-level
optimization, CSE still simplifies the following to "return 0;".
int
foo (int a)
{
return 0 % a;
}
Kazu Hirata
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19723
