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From: "vries at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug tree-optimization/65440] pass_lim misses support for predicated code motion Date: Mon, 16 Mar 2015 14:39:00 -0000 [thread overview] Message-ID: <bug-65440-4-QffzyPfuRO@http.gcc.gnu.org/bugzilla/> (raw) In-Reply-To: <bug-65440-4@http.gcc.gnu.org/bugzilla/> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65440 --- Comment #1 from vries at gcc dot gnu.org --- Concrete example ( based on example at https://gcc.gnu.org/git/?p=gcc.git;a=blob;f=gcc/tree-ssa-loop-im.c;h=9aba79ba776944ec6fba8459354deabe8c126b75;hb=HEAD#l333) test.c: ... #include <string.h> const char *something (void); size_t f (unsigned int n) { const char *s = something (); size_t sum = 0; size_t t; unsigned int i; for (i = 0; i < n; ++i) { if (s) t = strlen (s); else t = i * 2; sum += t; } return sum; } ... The resulting code with -O2 from the optimized dump is: ... f (unsigned int n) { unsigned int i; size_t t; size_t sum; const char * s; unsigned int _9; <bb 2>: s_6 = something (); if (n_7(D) != 0) goto <bb 3>; else goto <bb 8>; <bb 3>: # sum_13 = PHI <0(2)> # i_1 = PHI <0(2)> <bb 4>: # sum_14 = PHI <sum_13(3), sum_11(7)> # i_17 = PHI <i_1(3), i_12(7)> if (s_6 != 0B) goto <bb 5>; else goto <bb 6>; <bb 5>: t_8 = strlen (s_6); goto <bb 7>; <bb 6>: _9 = i_17 * 2; t_10 = (size_t) _9; <bb 7>: # t_2 = PHI <t_8(5), t_10(6)> sum_11 = t_2 + sum_14; i_12 = i_17 + 1; if (n_7(D) != i_12) goto <bb 4>; else goto <bb 8>; <bb 8>: # sum_16 = PHI <sum_11(7), 0(2)> return sum_16; } ... [ The same code is generated with -O3 -fno-tree-vectorize -fno-unswitch-loops. -funswitch-loops manages to take the strlen out of the loop, but by generating two loops. ]
next prev parent reply other threads:[~2015-03-16 14:39 UTC|newest] Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top 2015-03-16 14:27 [Bug tree-optimization/65440] New: " vries at gcc dot gnu.org 2015-03-16 14:39 ` vries at gcc dot gnu.org [this message] 2015-03-16 14:58 ` [Bug tree-optimization/65440] " vries at gcc dot gnu.org 2015-03-18 11:36 ` rguenth at gcc dot gnu.org
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