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From: "nakacristo at hotmail dot com" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug c/56463] infinite loop when having integer overflow in a simple accumulator Date: Wed, 27 Feb 2013 08:19:00 -0000 [thread overview] Message-ID: <bug-56463-4-JW1olteIBg@http.gcc.gnu.org/bugzilla/> (raw) In-Reply-To: <bug-56463-4@http.gcc.gnu.org/bugzilla/> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56463 --- Comment #5 from Cristóbal Camarero <nakacristo at hotmail dot com> 2013-02-27 08:19:04 UTC --- Dominique, I think the test I found is more problematic than yours. Since in mine, the huge value is completely independent of the ending condition. Hence most people would expect the loop to end without care of what happens to the accumulator variable 'a'. Exploring the intermediate steps of my test (with gcc test.c -O2 -fdump-tree-all) I see that in test.c.119t.ivopts the condition of the loop is changed from 'ivtmp.8_3 != 0' to 'a_25 != 1267128320', which would be correct considering overflow. From here the situation must be similar to Dominique's examples. In test.c.123t.vrp2 we see that the Value Range Propagation has decided that the ending condition never happens, probably because the ranges have no modular considerations. The ending condition and the printf are eliminated. In a later stage the infinite loop is substituted by an empty infinite loop. I suppose that this is not technically a bug. However, the lack of warning IS a bug. And a coherent behaviour would still being a good enhancement.
next prev parent reply other threads:[~2013-02-27 8:19 UTC|newest] Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top 2013-02-26 16:06 [Bug c/56463] New: " nakacristo at hotmail dot com 2013-02-26 16:16 ` [Bug c/56463] " jakub at gcc dot gnu.org 2013-02-26 17:40 ` nakacristo at hotmail dot com 2013-02-26 17:54 ` jakub at gcc dot gnu.org 2013-02-26 18:42 ` dominiq at lps dot ens.fr 2013-02-27 8:19 ` nakacristo at hotmail dot com [this message] 2013-02-27 8:31 ` jakub at gcc dot gnu.org 2013-12-02 19:03 ` Joost.VandeVondele at mat dot ethz.ch 2013-12-02 19:04 ` Joost.VandeVondele at mat dot ethz.ch
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