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RE: Why doesn't GCC generate conditional move for COND_EXPR?
Thanks, Andrew. I also implemented a quick patch on our port (based on GCC 4.5).
I noticed it produced better code now for our applications. Maybe eliminating
control flow in earlier stage helps other optimizing passes. Currently, tree
if-conversion pass is not turned on by default (only with tree vectorization
or some other passes). Maybe it is worth to make it default at -O2 (for those
processors support conditional move)?
> -----Original Message-----
> From: Andrew Pinski [mailto:firstname.lastname@example.org]
> Sent: 24 October 2011 17:20
> To: Richard Guenther
> Cc: Bingfeng Mei; email@example.com
> Subject: Re: Why doesn't GCC generate conditional move for COND_EXPR?
> On Mon, Oct 24, 2011 at 7:00 AM, Richard Guenther
> <firstname.lastname@example.org> wrote:
> > On Mon, Oct 24, 2011 at 2:55 PM, Bingfeng Mei <email@example.com>
> >> Hello,
> >> I noticed that COND_EXPR is not expanded to conditional move
> >> as MIN_EXPR/MAX_EXPR are (assuming movmodecc is available).
> >> I wonder why not?
> >> I have some loop that fails tree vectorization, but still contains
> >> COND_EXPR from tree ifcvt pass. In the end, the generated code
> >> is worse than if I don't turned -ftree-vectorize on. ÂThis
> >> is on our private port.
> > Because nobody touched COND_EXPR expansion since ages.
> I have a patch which I will be submitting next week or so that does
> this expansion correctly. In fact I have a few patches which improves
> the generation of COND_EXPR in simple cases (in PHI-OPT).
> Andrew Pinski