From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 38581 invoked by alias); 6 Mar 2015 08:41:17 -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 38490 invoked by uid 55); 6 Mar 2015 08:41:12 -0000 From: "rguenther at suse dot de" To: gcc-bugs@gcc.gnu.org Subject: [Bug rtl-optimization/65321] [5 Regression] ICE on valid code at -O2 and -O3 with -g enabled in decompose, at rtl.h:2007 Date: Fri, 06 Mar 2015 08:41:00 -0000 X-Bugzilla-Reason: CC X-Bugzilla-Type: changed X-Bugzilla-Watch-Reason: None X-Bugzilla-Product: gcc X-Bugzilla-Component: rtl-optimization X-Bugzilla-Version: 5.0 X-Bugzilla-Keywords: X-Bugzilla-Severity: normal X-Bugzilla-Who: rguenther at suse dot de X-Bugzilla-Status: ASSIGNED X-Bugzilla-Priority: P1 X-Bugzilla-Assigned-To: rguenth at gcc dot gnu.org X-Bugzilla-Target-Milestone: 5.0 X-Bugzilla-Flags: X-Bugzilla-Changed-Fields: Message-ID: In-Reply-To: References: Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit X-Bugzilla-URL: http://gcc.gnu.org/bugzilla/ Auto-Submitted: auto-generated MIME-Version: 1.0 X-SW-Source: 2015-03/txt/msg00687.txt.bz2 https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65321 --- Comment #5 from rguenther at suse dot de --- On Thu, 5 Mar 2015, rsandifo at gcc dot gnu.org wrote: > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65321 > > --- Comment #4 from rsandifo at gcc dot gnu.org --- > (In reply to Richard Biener from comment #3) > > (gdb) p debug_rtx (x.first) > > (const_int 128 [0x80]) > > (gdb) p x.second > > $2 = QImode > > (gdb) p precision > > $3 = 8 > > > > the CONST_INT is not properly sign-extended. This is from > > > > #6 0x0000000000d55381 in simplify_const_binary_operation (code=ASHIFT, > > mode=QImode, op0=0x7ffff68d3490, op1=0x7ffff69e8b00) > > at /space/rguenther/src/svn/trunk2/gcc/simplify-rtx.c:4001 > > ... > > 3997 case LSHIFTRT: > > 3998 case ASHIFTRT: > > 3999 case ASHIFT: > > 4000 { > > 4001 wide_int wop1 = pop1; > > 4002 if (SHIFT_COUNT_TRUNCATED) > > 4003 wop1 = wi::umod_trunc (wop1, width); > > > > but of course the shift amount need not be QImode as well. 128 is quite > > large, > > but well... > > > > Fact is that we don't know the mode of op1 here. From the fact that the > > const_int is not sign-extended we can conclude its mode is larger than > > QImode. > > And we will truncate it anyway (or return NULL_RTX) if it is too large, so > > it doesn't even matter. > > I take your point, but at the same time, is it really worth supporting shifts > whose shift amount is wider than the shifted value? ISTM that no .md pattern > would want such a thing, so in practice this would only ever happen with debug > exprs. Well, simplifying such shift may occur in regular code as well. We simply drop the extra bits (or fail to simplify), but that's done with wide-int stuff so we need to be able to convert the RTX to a wide-int first... (chicken and egg issue). > I think the safest fix would be to make use_narrower_mode{,_test} > narrow the shift amount if it is wider than the target mode. Just tried that > locally and it seems to fix the test case. No, that doesn't work. It will change behavior for say a shift of a QImode value by 0x101 because you'd obtain one for the shift value and thus the path taken will be different. ISTR that the difference with respect to implementations is whether a shift by 0x101 will result in a shift by 1 (SHIFT_COUNT_TRUNCATED) or whether it will result in zero (shift by too large value). So we need to either saturate (for !SHIFT_COUNT_TRUNCATED) or truncate (for SHIFT_COUNT_TRUNCATED). > > I think we can simply use > > > > wide_int wop1 = std::make_pair (op1, MAX_MODE_INT); > > > > here (or SImode maybe). Or have a "don't care" way to make a wide-int > > from a CONST_INT directly. > > Certainly SImode would be dangerous, since there's nothing to stop the same bug > reappearing with DImode. MAX_MODE_INT is a problem because it can be wider > than MAX_BITSIZE_MODE_ANY_INT on targets like x86_64 that explicitly override > the wide_int size. And I'd be reluctant to relax the general CONST_INT > semantics for such an oddball case. Well, the real fix is to pass down the mode - which may be not available, of course. Or simply declare that the shift amount has to be the same mode as the shifted value and properly create the RTL in the first place (honoring SHIFT_COUNT_TRUNCATED in the correct way).