public inbox for gcc-bugs@sourceware.org help / color / mirror / Atom feed
From: "msebor at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug tree-optimization/94675] [9 regression] -Warray-bounds false positive with -O2 Date: Mon, 20 Apr 2020 22:16:33 +0000 [thread overview] Message-ID: <bug-94675-4-YfzU9ynG2o@http.gcc.gnu.org/bugzilla/> (raw) In-Reply-To: <bug-94675-4@http.gcc.gnu.org/bugzilla/> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94675 Martin Sebor <msebor at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |msebor at gcc dot gnu.org --- Comment #1 from Martin Sebor <msebor at gcc dot gnu.org> --- The false positive is not due a shortcoming of the warning but rather due to GCC not having a sufficiently sophisticated analysis of relationships of pointers into the same objects. The same warning (and probably a numbers as well) can be reproduced with a simpler example. $ cat pr94675.c && gcc -O2 -S -Wall -fdump-tree-vrp=/dev/stdout pr94675.c unsigned char c, n; int f (void) { if (n <= 7) return 0; unsigned char *p = &c, *q = p + n; if (q - p <= 7) // not eliminated return 0; return p[7]; // spurious -Warray-bounds } ;; Function f (f, funcdef_no=0, decl_uid=1932, cgraph_uid=1, symbol_order=2) ;; 1 loops found ;; ;; Loop 0 ;; header 0, latch 1 ;; depth 0, outer -1 ;; nodes: 0 1 2 3 4 ;; 2 succs { 4 3 } ;; 3 succs { 4 } ;; 4 succs { 1 } Value ranges after VRP: n.0_1: unsigned char VARYING _2: unsigned char VARYING _3: int [0, 255] _5: int [0, 255] pr94675.c: In function ‘f’: pr94675.c:12:11: warning: array subscript 7 is outside array bounds of ‘unsigned char[1]’ [-Warray-bounds] 12 | return p[7]; | ~^~~ pr94675.c:1:15: note: while referencing ‘c’ 1 | unsigned char c, n; | ^ f () { unsigned char n.0_1; unsigned char _2; int _3; int _5; <bb 2> [local count: 1073741824]: n.0_1 = n; if (n.0_1 <= 7) goto <bb 4>; [34.00%] else goto <bb 3>; [66.00%] <bb 3> [local count: 708669601]: _2 = MEM[(unsigned char *)&c + 7B]; _5 = (int) _2; <bb 4> [local count: 1073741824]: # _3 = PHI <0(2), _5(3)> return _3; } ;; Function f (f, funcdef_no=0, decl_uid=1932, cgraph_uid=1, symbol_order=2) ;; 1 loops found ;; ;; Loop 0 ;; header 0, latch 1 ;; depth 0, outer -1 ;; nodes: 0 1 2 3 4 ;; 2 succs { 4 3 } ;; 3 succs { 4 } ;; 4 succs { 1 } Value ranges after VRP: n.0_1: unsigned char VARYING _2: unsigned char VARYING _3: int [0, 255] _5: int [0, 255] f () { unsigned char n.0_1; unsigned char _2; int _3; int _5; <bb 2> [local count: 1073741824]: n.0_1 = n; if (n.0_1 <= 7) goto <bb 4>; [34.00%] else goto <bb 3>; [66.00%] <bb 3> [local count: 708669601]: _2 = MEM[(unsigned char *)&c + 7B]; _5 = (int) _2; <bb 4> [local count: 1073741824]: # _3 = PHI <_5(3), 0(2)> return _3; }
next prev parent reply other threads:[~2020-04-20 22:16 UTC|newest] Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top 2020-04-20 19:42 [Bug tree-optimization/94675] New: " chantry.xavier at gmail dot com 2020-04-20 22:16 ` msebor at gcc dot gnu.org [this message] 2020-04-21 6:51 ` [Bug tree-optimization/94675] " chantry.xavier at gmail dot com 2020-04-21 7:04 ` marxin at gcc dot gnu.org 2020-04-21 7:46 ` rguenth at gcc dot gnu.org 2020-04-21 7:58 ` [Bug tree-optimization/94675] [9/10 " rguenth at gcc dot gnu.org 2020-04-21 7:59 ` jakub at gcc dot gnu.org 2020-04-21 8:06 ` [Bug tree-optimization/94675] [9/10 regression] -Warray-bounds false positive with -O2 since r9-1948 jakub at gcc dot gnu.org 2020-04-21 14:03 ` law at redhat dot com 2020-04-21 14:18 ` rguenther at suse dot de 2020-04-21 14:43 ` law at redhat dot com 2020-04-21 14:57 ` rguenther at suse dot de 2020-04-21 14:58 ` msebor at gcc dot gnu.org 2020-04-21 19:14 ` law at redhat dot com 2020-04-21 19:16 ` law at redhat dot com 2020-04-21 20:10 ` law at redhat dot com 2020-04-21 21:00 ` msebor at gcc dot gnu.org 2020-04-22 6:34 ` rguenther at suse dot de 2020-04-24 7:48 ` chantry.xavier at gmail dot com 2020-04-24 15:16 ` msebor at gcc dot gnu.org 2020-04-30 13:12 ` chantry.xavier at gmail dot com 2021-06-01 8:17 ` [Bug tree-optimization/94675] [9/10/11/12 " rguenth at gcc dot gnu.org 2021-09-06 11:25 ` pinskia at gcc dot gnu.org 2022-03-16 11:09 ` chantry.xavier at gmail dot com 2022-03-16 13:24 ` rguenth at gcc dot gnu.org 2022-05-27 9:42 ` [Bug tree-optimization/94675] [10/11/12/13 " rguenth at gcc dot gnu.org 2022-06-28 10:40 ` jakub at gcc dot gnu.org 2023-05-14 21:25 ` [Bug tree-optimization/94675] [10/11/12/13/14 " pinskia at gcc dot gnu.org 2023-07-07 10:37 ` [Bug tree-optimization/94675] [11/12/13/14 " rguenth at gcc dot gnu.org
Reply instructions: You may reply publicly to this message via plain-text email using any one of the following methods: * Save the following mbox file, import it into your mail client, and reply-to-all from there: mbox Avoid top-posting and favor interleaved quoting: https://en.wikipedia.org/wiki/Posting_style#Interleaved_style * Reply using the --to, --cc, and --in-reply-to switches of git-send-email(1): git send-email \ --in-reply-to=bug-94675-4-YfzU9ynG2o@http.gcc.gnu.org/bugzilla/ \ --to=gcc-bugzilla@gcc.gnu.org \ --cc=gcc-bugs@gcc.gnu.org \ /path/to/YOUR_REPLY https://kernel.org/pub/software/scm/git/docs/git-send-email.html * If your mail client supports setting the In-Reply-To header via mailto: links, try the mailto: linkBe sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions for how to clone and mirror all data and code used for this inbox; as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).