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From: "hubicka at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug tree-optimization/55079] [4.8 regression] false positive -Warray-bounds (also seen at -O3 bootstrap) Date: Wed, 14 Nov 2012 19:31:00 -0000 [thread overview] Message-ID: <bug-55079-4-eVLL9gc69B@http.gcc.gnu.org/bugzilla/> (raw) In-Reply-To: <bug-55079-4@http.gcc.gnu.org/bugzilla/> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55079 Jan Hubicka <hubicka at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Summary|[4.8 regression] false |[4.8 regression] false |positive -Warray-bounds |positive -Warray-bounds | |(also seen at -O3 | |bootstrap) --- Comment #8 from Jan Hubicka <hubicka at gcc dot gnu.org> 2012-11-14 19:31:16 UTC --- Hi, at -O3 bootstrap we have false positive on simplify-rtx.c ../../gcc/simplify-rtx.c: In function ‘rtx_def* simplify_plus_minus(rtx_code, machine_mode, rtx, rtx)’: ../../gcc/simplify-rtx.c:4285:63: warning: array subscript is below array bounds [-Warray-bounds] while (j-- && simplify_plus_minus_op_data_cmp (ops[j].op, save.op)); the siplified testcase is as follows: int a[8]; void test(unsigned int n) { unsigned int i; unsigned int j; if (n<8) for (j=0;j<n;j++) { i = j; do a[i+1]=a[i]; while (i--); } } here we unroll the inner do loop 7 times based on the array bounds derived from [i] access. Afterwards VRP proves that j is always at most 7 and thus the loop walks out of bounds. Here we may be able to determine that the loop accesses both i and i+1 and we could actually unroll only 6 times, but we handle each of array access independently.
next prev parent reply other threads:[~2012-11-14 19:31 UTC|newest] Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top 2012-10-26 9:56 [Bug tree-optimization/55079] New: [4.8 regeression] false positive -Warray-bounds dimhen at gmail dot com 2012-10-26 10:09 ` [Bug tree-optimization/55079] " rguenth at gcc dot gnu.org 2012-10-30 9:34 ` [Bug tree-optimization/55079] [4.8 regression] " rguenth at gcc dot gnu.org 2012-10-30 9:35 ` rguenth at gcc dot gnu.org 2012-11-02 16:35 ` hubicka at gcc dot gnu.org 2012-11-02 16:47 ` hubicka at gcc dot gnu.org 2012-11-02 18:45 ` hubicka at gcc dot gnu.org 2012-11-02 20:51 ` hubicka at gcc dot gnu.org 2012-11-14 19:31 ` hubicka at gcc dot gnu.org [this message] 2012-11-15 1:01 ` [Bug tree-optimization/55079] [4.8 regression] false positive -Warray-bounds (also seen at -O3 bootstrap) hubicka at gcc dot gnu.org 2012-12-07 12:55 ` rguenth at gcc dot gnu.org 2012-12-10 13:23 ` rguenth at gcc dot gnu.org 2012-12-10 13:50 ` rguenth at gcc dot gnu.org 2012-12-10 14:14 ` rguenth at gcc dot gnu.org 2012-12-10 16:27 ` hubicka at ucw dot cz 2012-12-11 10:06 ` rguenth at gcc dot gnu.org 2012-12-11 10:08 ` rguenth at gcc dot gnu.org 2012-12-12 9:33 ` schwab at gcc dot gnu.org
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