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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug tree-optimization/62006] Bad code generation with -O3 (possibly due to -ftree-partial-pre) Date: Mon, 04 Aug 2014 12:00:00 -0000 [thread overview] Message-ID: <bug-62006-4-fvOgPGJoLb@http.gcc.gnu.org/bugzilla/> (raw) In-Reply-To: <bug-62006-4@http.gcc.gnu.org/bugzilla/> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=62006 --- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> --- It looks ok what PRE does (it's not really a partial partial redundancy but a full redundndancy). The bug also reproduces with -O2 -ftree-partial-pre. Disabling loop optimizations and cddce2 hides the bug. With PPRE enabled CDDCE2 removes the stores to D.46421.diff (again I see nothing wrong with doing that). Btw, this all happens in _M_range_initialize. (-fno-strict-aliasing fixes the bug as well). Note that I see stores as OffPtrBase to automatic objects: - MEM[(struct OffPtrBase *)&D.46421].diff = _70; and loads from OffPtr via this: _16 = &MEM[(struct OffPtr *)this_4(D)].D.43564; or remaining stores: MEM[(struct OffPtrBase *)this_4(D) + 16B].diff = iftmp.15_41; I also see: _74 = (sizetype) _47; iftmp.10_75 = &D.46429.D.43564 + _74; __last.3_77 = (long int) iftmp.10_75; __first.4_78 = (long int) &D.46430.D.43564; _79 = __last.3_77 - __first.4_78; which effectively subtracts two unrelated addresses of automatic objects (boooo - undefined behavior!) I think the testcase is simply bogus. Can you explain what the "fancy" pointers do? Disabling points-to analysis also "fixes" the testcase. Note that with points-to analysis you cannot reach any other object with offsetting the address of an object.
next prev parent reply other threads:[~2014-08-04 12:00 UTC|newest] Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top 2014-08-04 10:40 [Bug c++/62006] New: " tkoeppe at google dot com 2014-08-04 10:55 ` [Bug tree-optimization/62006] " redi at gcc dot gnu.org 2014-08-04 11:24 ` rguenth at gcc dot gnu.org 2014-08-04 12:00 ` rguenth at gcc dot gnu.org [this message] 2014-08-04 12:05 ` tkoeppe at google dot com 2014-08-04 12:13 ` rguenth at gcc dot gnu.org 2014-08-04 13:20 ` rguenth at gcc dot gnu.org 2014-08-04 13:23 ` rguenth at gcc dot gnu.org 2014-08-04 13:31 ` tkoeppe at google dot com 2014-08-04 13:44 ` rguenther at suse dot de 2014-08-05 13:06 ` rguenth at gcc dot gnu.org
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