From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 16179 invoked by alias); 29 Apr 2013 17:37:07 -0000 Mailing-List: contact gcc-bugs-help@gcc.gnu.org; run by ezmlm Precedence: bulk List-Id: List-Archive: List-Post: List-Help: Sender: gcc-bugs-owner@gcc.gnu.org Received: (qmail 16133 invoked by uid 48); 29 Apr 2013 17:37:05 -0000 From: "ubizjak at gmail dot com" 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 X-Bugzilla-Reason: CC X-Bugzilla-Type: changed X-Bugzilla-Watch-Reason: None X-Bugzilla-Product: gcc X-Bugzilla-Component: target X-Bugzilla-Keywords: wrong-code X-Bugzilla-Severity: normal X-Bugzilla-Who: ubizjak at gmail dot com X-Bugzilla-Status: NEW X-Bugzilla-Priority: P3 X-Bugzilla-Assigned-To: unassigned at gcc dot gnu.org X-Bugzilla-Target-Milestone: --- X-Bugzilla-Changed-Fields: Message-ID: In-Reply-To: References: X-Bugzilla-URL: http://gcc.gnu.org/bugzilla/ Auto-Submitted: auto-generated Content-Type: text/plain; charset="UTF-8" MIME-Version: 1.0 X-SW-Source: 2013-04/txt/msg02364.txt.bz2 http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44578 --- Comment #10 from Uros Bizjak 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.