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Re: [Bug tree-optimization/19723] [4.0 Regression] A side effect is missed in 0 % a++.
- From: Richard Henderson <rth at gcc dot gnu dot org>
- To: Jeffrey A Law <law at redhat dot com>
- Cc: gcc-bugzilla at gcc dot gnu dot org, gcc-patches at gcc dot gnu dot org
- Date: Mon, 31 Jan 2005 22:36:22 -0800
- Subject: Re: [Bug tree-optimization/19723] [4.0 Regression] A side effect is missed in 0 % a++.
- References: <20050131134136.19723.kazu@cs.umass.edu> <20050131173323.22919.qmail@sourceware.org> <1107229535.20928.22.camel@localhost.localdomain>
On Mon, Jan 31, 2005 at 08:45:34PM -0700, Jeffrey A Law wrote:
> + /* 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.
r~