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From: "jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug middle-end/64491] [5 Regression] incorrect warning: loop exit may only be reached after undefined behavior Date: Wed, 18 Feb 2015 13:57:00 -0000 [thread overview] Message-ID: <bug-64491-4-7qzYYxpMju@http.gcc.gnu.org/bugzilla/> (raw) In-Reply-To: <bug-64491-4@http.gcc.gnu.org/bugzilla/> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64491 Jakub Jelinek <jakub at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |ams at gcc dot gnu.org, | |jakub at gcc dot gnu.org --- Comment #7 from Jakub Jelinek <jakub at gcc dot gnu.org> --- I think this is just a bogus warning introduced in r217891, the generated code looks ok. Code like: <bb 5>: # f_27 = PHI <f_23(4), f_17(8)> if (f_27 != 0) goto <bb 6>; else goto <bb 7>; <bb 6>: _11 = f_27 + -1; iftmp.0_12 = A[_11]; if (f_27 != 7) goto <bb 7>; else goto <bb 8>; <bb 7>: # iftmp.0_28 = PHI <iftmp.0_12(6), 0(5)> _13 = f_27 + 1; iftmp.1_14 = A[_13]; <bb 8>: # iftmp.1_4 = PHI <iftmp.1_14(7), 0(6)> # iftmp.0_29 = PHI <iftmp.0_28(7), iftmp.0_12(6)> _15 = iftmp.0_29 | iftmp.1_4; B[f_27] = _15; f_17 = f_27 + 1; if (f_17 == 8) goto <bb 9>; else goto <bb 5>; is transformed by dom1 into an extra early exit from the loop, if f_27 == 7, we jump to a new bb outside of the loop that does: <bb 11>: # iftmp.1_2 = PHI <0(6)> # iftmp.0_3 = PHI <iftmp.0_12(6)> _1 = iftmp.0_3 | iftmp.1_2; B[f_27] = _1; f_26 = f_27 + 1; goto <bb 10>; But indeed dom nor anything else doesn't figure out that the f_17 == 8 exit condition of the loop is then never true, the loop will always exit through the jump to bb 11. Supposedly the warning needs to be limited to the case where the loop has only a single exit, or when the undefined behavior occurs on all loop exits.
next prev parent reply other threads:[~2015-02-18 13:57 UTC|newest] Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top 2015-01-04 20:24 [Bug c++/64491] New: " stuwph at live dot de 2015-01-04 20:46 ` [Bug c++/64491] " redi at gcc dot gnu.org 2015-01-10 15:58 ` joona.kiiski at iki dot fi 2015-01-10 16:04 ` joona.kiiski at iki dot fi 2015-01-10 16:49 ` [Bug c++/64491] [5 Regression] incorrect " Joost.VandeVondele at mat dot ethz.ch 2015-01-11 22:10 ` [Bug middle-end/64491] " joona.kiiski at gmail dot com 2015-01-12 7:18 ` Joost.VandeVondele at mat dot ethz.ch 2015-02-09 0:06 ` pinskia at gcc dot gnu.org 2015-02-18 13:57 ` jakub at gcc dot gnu.org [this message] 2015-02-18 16:25 ` ams at gcc dot gnu.org 2015-02-18 16:28 ` jakub at gcc dot gnu.org 2015-02-20 11:28 ` ams at gcc dot gnu.org 2015-02-24 17:01 ` ams at gcc dot gnu.org 2015-02-24 19:18 ` jakub at gcc dot gnu.org 2015-03-18 12:50 ` rguenth at gcc dot gnu.org 2015-03-18 12:53 ` jakub at gcc dot gnu.org 2015-03-18 14:27 ` ams at gcc dot gnu.org 2015-03-18 14:29 ` ams at gcc dot gnu.org
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