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From: "rakdver at gcc dot gnu dot org" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug tree-optimization/25985] [4.2 Regression] with optimization integer math fails Date: Thu, 16 Mar 2006 03:15:00 -0000 [thread overview] Message-ID: <20060316031539.2203.qmail@sourceware.org> (raw) In-Reply-To: <bug-25985-9034@http.gcc.gnu.org/bugzilla/> ------- Comment #6 from rakdver at gcc dot gnu dot org 2006-03-16 03:15 ------- Actually, my previous comment is wrong, it is ivcanon (more precisely, # of iterations analysis). Consider this testcase: #include <stdio.h> void bla(int x) { if (x < -100) exit (0); } int main(void) { int bits = 25; while (bits) { printf ("%d\n", bits); bla(bits); bits -= 8; } return 0; } We note that bits is signed, therefore it cannot overflow, and conclude the loop must be finite. Using this assumption, we conclude it iterates two times. However, this would only be correct if the loop were exited through this particular exit, as these examples demonstrate. -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=25985
next prev parent reply other threads:[~2006-03-16 3:15 UTC|newest] Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top 2006-01-26 23:13 [Bug c/25985] New: " jurka at ejurka dot com 2006-01-26 23:28 ` [Bug middle-end/25985] [4.2 Regression] " pinskia at gcc dot gnu dot org 2006-02-20 17:50 ` [Bug tree-optimization/25985] " pinskia at gcc dot gnu dot org 2006-03-15 18:27 ` pinskia at gcc dot gnu dot org 2006-03-15 18:40 ` pinskia at gcc dot gnu dot org 2006-03-15 20:15 ` rguenth at gcc dot gnu dot org 2006-03-15 20:22 ` rakdver at gcc dot gnu dot org 2006-03-16 2:49 ` rakdver at gcc dot gnu dot org 2006-03-16 3:15 ` rakdver at gcc dot gnu dot org [this message] 2006-03-16 14:29 ` rakdver at gcc dot gnu dot org 2006-03-29 1:41 ` rakdver at gcc dot gnu dot org 2006-04-11 23:13 ` pinskia at gcc dot gnu dot org 2006-05-04 6:40 ` jakub at gcc dot gnu dot org
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