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Re: GCC 2.7.2.3 good, EGCS 1.0.3 bad for x86 subtract then test
- To: Richard Henderson <rth at cygnus dot com>
- Subject: Re: GCC 2.7.2.3 good, EGCS 1.0.3 bad for x86 subtract then test
- From: Jeffrey A Law <law at hurl dot cygnus dot com>
- Date: Wed, 23 Dec 1998 21:55:08 -0700
- cc: Jamie Lokier <egcs at tantalophile dot demon dot co dot uk>, Marc Lehmann <pcg at goof dot com>, egcs at cygnus dot com
- Reply-To: law at cygnus dot com
In message <19981223141815.C12309@dot.cygnus.com>you write:
> On Mon, Dec 21, 1998 at 10:52:13AM +0000, Jamie Lokier wrote:
> > Here's the example program:
> >
> > extern void a (void);
> >
> > void f (int x, int y)
> > {
> > if ((x -= y) >= 0)
> > a ();
> > }
>
> This is solved by a patch Jeff sent me just yesterday.
Yea. But it seems to generally create worse code -- too aggressive about
copying the source to the destination. Some tweaking of the heuristic for
when to copy the source to the destination may be needed to make the change
generally useful.
jeff