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Re: [PATCH] Fix PR 61225

From: Jeff Law <law at redhat dot com>
To: Segher Boessenkool <segher at kernel dot crashing dot org>, Zhenqiang Chen <zhenqiang dot chen at arm dot com>
Cc: Steven Bosscher <stevenb dot gcc at gmail dot com>, gcc-patches at gcc dot gnu dot org, Jakub Jelinek <jakub at redhat dot com>
Date: Fri, 05 Dec 2014 15:31:54 -0700
Subject: Re: [PATCH] Fix PR 61225
Authentication-results: sourceware.org; auth=none
References: <CACgzC7A7+JXBQ-HCcoqjhmbjoALCi8nngJy2J8SXHF1GRvyQPQ at mail dot gmail dot com> <CABu31nP5TqCU3iB-3jBTU93bORrCAmohq5nzcVBdjx2cqabrzA at mail dot gmail dot com> <CACgzC7D40=bxqag59GYQuXtze_ZAquo3PhpLmh0EGxZte5Mw4A at mail dot gmail dot com> <53C73EBD dot 9070909 at redhat dot com> <CACgzC7CJnoaOsFMDjXDZ0CLiECWPbejxDHg2GOk_AUtjrzC80w at mail dot gmail dot com> <547CE75B dot 6090709 at redhat dot com> <000001d00f9e$64f43600$2edca200$ at arm dot com> <20141204204956 dot GA11759 at gate dot crashing dot org>

On 12/04/14 13:49, Segher Boessenkool wrote:

On Thu, Dec 04, 2014 at 04:43:34PM +0800, Zhenqiang Chen wrote:

C code:

     if (!--*p)

rtl code:

     6: r91:SI=[r90:SI]
     7: {r88:SI=r91:SI-0x1;clobber flags:CC;}
     8: [r90:SI]=r88:SI
     9: flags:CCZ=cmp(r88:SI,0)

expected output:

     8: {flags:CCZ=cmp([r90:SI]-0x1,0);[r90:SI]=[r90:SI]-0x1;}

in assemble, it is

   decl (%eax)


Combine does not consider combining 9 into 7 because there is no LOG_LINK
between them (the link for r88 is between 8 and 7 already).

OK, yea, that's a long standing design decision. We don't feed a singledef into multiple use sites.


jeff

Follow-Ups:
- Re: [PATCH] Fix PR 61225
  - From: Segher Boessenkool

References:
- Re: [PATCH] Fix PR 61225
  - From: Jeff Law
- RE: [PATCH] Fix PR 61225
  - From: Zhenqiang Chen
- Re: [PATCH] Fix PR 61225
  - From: Segher Boessenkool

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