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From: "glisse at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug tree-optimization/100366] spurious warning - std::vector::clear followed by std::vector::insert(vec.end(), ...) with -O2 Date: Wed, 05 May 2021 10:55:38 +0000 [thread overview] Message-ID: <bug-100366-4-qjRNDcPPP1@http.gcc.gnu.org/bugzilla/> (raw) In-Reply-To: <bug-100366-4@http.gcc.gnu.org/bugzilla/> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100366 --- Comment #5 from Marc Glisse <glisse at gcc dot gnu.org> --- (In reply to Martin Sebor from comment #2) > The IL looks like the warning is justified: The memcpy call is dead code, we just fail to notice it. > <bb 13> [local count: 230225493]: > # prephitmp_42 = PHI <_6(4), _7(3)> This is always _6, because in bb 3 we have _6 == _7. > pretmp_67 = vec_2(D)->D.33449._M_impl.D.32762._M_start; > _69 = prephitmp_42 - pretmp_67; Always 0. > <bb 7> [local count: 220460391]: > MEM <unsigned int> [(char * {ref-all})_155] = pretmp_72; > _50 = vec_2(D)->D.33449._M_impl.D.32762._M_finish; > _Num_51 = _50 - prephitmp_42; Always 0, in bb 4 we copy _M_start in _M_finish if they are not already equal. (sorry for the wrong FRE comment earlier) Note that if I replace operator new/delete with malloc/free inline void* operator new(std::size_t n){return __builtin_malloc(n);} inline void operator delete(void*p)noexcept{__builtin_free(p);} inline void operator delete(void*p,std::size_t)noexcept{__builtin_free(p);} we optimize quite a bit more and the warning disappears.
next prev parent reply other threads:[~2021-05-05 10:55 UTC|newest] Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-05-01 2:36 [Bug c++/100366] New: " mrsam@courier-mta.com 2021-05-02 11:27 ` [Bug tree-optimization/100366] " glisse at gcc dot gnu.org 2021-05-03 17:51 ` msebor at gcc dot gnu.org 2021-05-03 21:02 ` mrsam@courier-mta.com 2021-05-04 7:39 ` rguenth at gcc dot gnu.org 2021-05-05 10:55 ` glisse at gcc dot gnu.org [this message] 2021-05-05 11:01 ` glisse at gcc dot gnu.org 2021-05-05 11:15 ` glisse at gcc dot gnu.org 2021-05-05 12:18 ` mrsam@courier-mta.com 2021-05-12 23:44 ` msebor at gcc dot gnu.org 2021-12-02 21:14 ` msebor at gcc dot gnu.org 2021-12-06 16:45 ` [Bug tree-optimization/100366] [11/12 Regression] " roystgnr at ices dot utexas.edu 2021-12-28 12:09 ` pinskia at gcc dot gnu.org 2022-01-20 14:03 ` rguenth at gcc dot gnu.org 2022-04-21 7:49 ` rguenth at gcc dot gnu.org 2022-07-05 10:07 ` [Bug tree-optimization/100366] [11/12/13 " hewillk at gmail dot com 2022-11-26 15:53 ` zeranoe at gmail dot com 2022-11-29 15:58 ` redi at gcc dot gnu.org 2022-11-29 17:14 ` cvs-commit at gcc dot gnu.org 2023-04-20 13:57 ` [Bug tree-optimization/100366] [11/12 " cvs-commit at gcc dot gnu.org 2023-05-29 10:04 ` jakub at gcc dot gnu.org
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