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From: "ubizjak at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/44578] GCC generates MMX instructions but fails to generate "emms"
Date: Mon, 29 Apr 2013 17:37:00 -0000	[thread overview]
Message-ID: <bug-44578-4-yLpdhAcPi6@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-44578-4@http.gcc.gnu.org/bugzilla/>


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44578

--- Comment #10 from Uros Bizjak <ubizjak at gmail dot com> 2013-04-29 17:37:03 UTC ---
(In reply to comment #9)
> It does fix the issue I had in this test case. But theoretically can't
> this pattern still generate an MMX reference in some cases? And I see
> other instances of the same constraint in i386.md - is there a larger
> issue here and how can we prevent this?

Yes, leaks of MMX registers were quite problematic in the past. A lot of effort
went into insn patterns to balance register allocator to allow MMX registers
when necessary, and to avoid them otherwise. It looks that zero_extendsidi
pattern was skipped in these efforts.

-mno-mmx can be used to prevent MMX regs, but the allocator is quite well tuned
nowadays, so instantiation of %mmX registers when not strictly needed will be
considered a bug.


  parent reply	other threads:[~2013-04-29 17:37 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <bug-44578-4@http.gcc.gnu.org/bugzilla/>
2012-11-15  6:36 ` kl4yfd at gmail dot com
2012-11-15  6:39 ` kl4yfd at gmail dot com
2012-11-15 12:06 ` jakub at gcc dot gnu.org
2012-11-15 17:05 ` kl4yfd at gmail dot com
2013-04-29 16:44 ` tejohnson at google dot com
2013-04-29 17:13 ` ubizjak at gmail dot com
2013-04-29 17:24 ` tejohnson at google dot com
2013-04-29 17:37 ` ubizjak at gmail dot com [this message]
2013-04-30  5:38 ` ubizjak at gmail dot com
2013-04-30  5:43 ` tejohnson at google dot com
2013-04-30  5:53 ` ubizjak at gmail dot com
2013-04-30  6:07 ` ubizjak at gmail dot com
2010-06-18 10:27 [Bug target/44578] New: " stephen dot dolan at havok dot com
2010-06-18 10:46 ` [Bug target/44578] " rguenth at gcc dot gnu dot org
2010-06-19 17:23 ` ubizjak at gmail dot com

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