public inbox for gcc-bugs@sourceware.org help / color / mirror / Atom feed
From: "eggert at gnu dot org" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug c/48968] New: incorrect warning about longjmp/vfork clobbering a local (-W -O2, x86-64) Date: Wed, 11 May 2011 20:04:00 -0000 [thread overview] Message-ID: <bug-48968-4@http.gcc.gnu.org/bugzilla/> (raw) http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48968 Summary: incorrect warning about longjmp/vfork clobbering a local (-W -O2, x86-64) Product: gcc Version: 4.6.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c AssignedTo: unassigned@gcc.gnu.org ReportedBy: eggert@gnu.org The attached program u.i, derived from the Emacs trunk, has code of the following form: Lisp_Object XXXevent, tem; if (idx < 0) { XXXevent = Qnil; } else { Lisp_Object _l; _l.s.val = idx; _l.s.type = Lisp_Int; XXXevent = _l; } if ((((enum Lisp_Type) ((XXXevent)).u.type)) == Lisp_Int) { ... } These are the only defs and uses of XXXevent, which is a local variable of union type. When compiled with -W -O2 on x86-64, GCC 4.6.0 complains: error: variable 'XXXevent' might be clobbered by 'longjmp' or 'vfork' But no longjmp or vfork is possible between the time that XXXevent is set, and the time that it is used. I worry that this bogus warning is a symptom of deeper problems in GCC 4.6.0's optimizer. Here is the full output of: gcc -v -save-temps -S -W -Wno-missing-field-initializers -Wno-sign-compare -Werror -O2 u.i Using built-in specs. COLLECT_GCC=gcc COLLECT_LTO_WRAPPER=/usr/local_cs/linux/gcc-4.6.0/bin/../libexec/gcc/x86_64-unknown-linux-gnu/4.6.0/lto-wrapper Target: x86_64-unknown-linux-gnu Configured with: ../gcc-4.6.0/configure --prefix=/usr/local/cs/gcc-4.6.0 --with-gmp-include=/usr/local/cs/include --disable-nls --with-stage1-ldflags='-L/usr/local/cs/lib64 -Xlinker -rpath=/usr/local/cs/lib64' --with-boot-ldflags='-L/usr/local/cs/lib64 -Xlinker -rpath=/usr/local/cs/lib64' LDFLAGS='-L/usr/local/cs/lib64 -Xlinker -rpath=/usr/local/cs/lib64' Thread model: posix gcc version 4.6.0 (GCC) COLLECT_GCC_OPTIONS='-v' '-save-temps' '-S' '-Wextra' '-Wno-missing-field-initializers' '-Wno-sign-compare' '-Werror' '-O2' '-mtune=generic' '-march=x86-64' /usr/local_cs/linux/gcc-4.6.0/bin/../libexec/gcc/x86_64-unknown-linux-gnu/4.6.0/cc1 -fpreprocessed u.i -quiet -dumpbase u.i -mtune=generic -march=x86-64 -auxbase u -O2 -Wextra -Wno-missing-field-initializers -Wno-sign-compare -Werror -version -o u.s GNU C (GCC) version 4.6.0 (x86_64-unknown-linux-gnu) compiled by GNU C version 4.6.0, GMP version 5.0.2, MPFR version 3.0.1-p4, MPC version 0.9 GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072 GNU C (GCC) version 4.6.0 (x86_64-unknown-linux-gnu) compiled by GNU C version 4.6.0, GMP version 5.0.2, MPFR version 3.0.1-p4, MPC version 0.9 GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072 Compiler executable checksum: 48a4f3d76c3a714a5f5622b4f42440c5 u.i: In function 'read_char': u.i:60167:20: error: variable 'XXXevent' might be clobbered by 'longjmp' or 'vfork' [-Werror=clobbered] cc1: all warnings being treated as errors
next reply other threads:[~2011-05-11 20:03 UTC|newest] Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top 2011-05-11 20:04 eggert at gnu dot org [this message] 2011-05-11 20:00 ` [Bug c/48968] " eggert at gnu dot org 2011-05-12 11:07 ` rguenth at gcc dot gnu.org 2011-05-12 13:54 ` schwab@linux-m68k.org 2011-05-12 19:11 ` jakub at gcc dot gnu.org 2011-05-12 20:22 ` eggert at gnu dot org 2012-06-01 20:42 ` eggert at gnu dot org 2012-06-01 21:19 ` eggert at gnu dot org 2014-01-19 18:01 ` mpolacek at gcc dot gnu.org 2014-01-19 18:34 ` eggert at gnu dot org 2014-01-19 20:31 ` mpolacek 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-48968-4@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).