> From: Jeff Law [mailto:l...@redhat.com] > Sent: Tuesday, April 28, 2015 12:27 AM > To: Thomas Preud'homme; 'Eric Botcazou' > Cc: gcc-patches@gcc.gnu.org > Subject: Re: [PATCH, combine] Try REG_EQUAL for nonzero_bits > > On 04/27/2015 04:26 AM, Thomas Preud'homme wrote: > >> From: Jeff Law [mailto:l...@redhat.com] > >> Sent: Saturday, April 25, 2015 3:00 AM > >> Do you have a testcase where this change can result in better > generated > >> code. If so please add that testcase. It's OK if it's ARM specific. > > > > Hi Jeff, > > > > Last time I tried I couldn't reduce the code to a small testcase but if I > remember > > well it was mostly due to the problem of finding a good test for creduce > > (zero extension is not unique enough). I'll try again with a more manual > approach > > and get back to you. > OK. No need for heroics -- give it a shot, but don't burn an insane > amount of time on it. If we can't get to a reasonable testcase, then so > be it.
Sadly I couldn't get a testcase. I get almost same sequence of instruction as the program we found the problem into but couldn't get exactly the same. In all the cases I constructed the nonzero_bits info we already have were enough for combine to do its job. I couldn't find what cause this information to be inaccurate. I will try to investigate a bit further on Monday as another pass might not be doing its job properly. Or maybe there's something that prevent information being propagated. Best regards, Thomas
