This is the mail archive of the
gcc-patches@gcc.gnu.org
mailing list for the GCC project.
Re: [PATCH] Fix bitfield-- != 0 transformation in fold-const.c
- From: Roger Sayle <roger at eyesopen dot com>
- To: Paolo Bonzini <bonzini at gnu dot org>
- Cc: gcc-patches at gcc dot gnu dot org
- Date: Sat, 6 Mar 2004 15:26:57 -0700 (MST)
- Subject: Re: [PATCH] Fix bitfield-- != 0 transformation in fold-const.c
On Sun, 7 Mar 2004, Paolo Bonzini wrote:
> > Consider the following counter example, for unsigned short x,
> > "x-- > 0" is not equivalent to "--x > 65535". Notice that this
> > transformation only works for equality and inequality.
>
> But you can convert for signed short x, x-- > -32768 to --x > 32767,
> because overflow semantics are not defined.
Consider x equals zero. "x-- > -32768" is true, but "--x > 32767" isn't.
Roger
--