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From: "suochenyao at 163 dot com" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug c/97493] generate wrong code with "-Os -fno-toplevel-reorder -frename-registers" Date: Fri, 30 Oct 2020 15:28:25 +0000 [thread overview] Message-ID: <bug-97493-4-kuVpwalouv@http.gcc.gnu.org/bugzilla/> (raw) In-Reply-To: <bug-97493-4@http.gcc.gnu.org/bugzilla/> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97493 --- Comment #5 from suochenyao at 163 dot com <suochenyao at 163 dot com> --- ******************************************************************************* I think this can be reproduced with "-fno-strict-aliasing"... I am not sure whether it can be helpful... ******************************************************************************* OS and Platform: CentOS Linux release 7.8.2003 (Core), x86_64 GNU/Linux ******************************************************************************* Program: int printf(const char *, ...); union { long a; int b; } c; int d=0; long e=0; long *f = &c.a; short g=0; int *h = &c.b; short i(int j) { g = *h; *f = 3; for (;; e--) { if (*h) return d; *h = j; } return 0; } int main() { i(1); printf("%d\n", (int)e); return 0; } ******************************************************************************* gcc version: $ gcc -v Using built-in specs. COLLECT_GCC=/home/suocy/bin/gcc-dev/bin/gcc COLLECT_LTO_WRAPPER=/home/suocy/bin/gcc-dev/libexec/gcc/x86_64-pc-linux-gnu/11.0.0/lto-wrapper Target: x86_64-pc-linux-gnu Configured with: ../configure --prefix=/home/suocy/bin/gcc-dev/ --disable-multilib --enable-languages=c,c++ Thread model: posix Supported LTO compression algorithms: zlib gcc version 11.0.0 20201029 (experimental) (GCC) ******************************************************************************* Command Lines: $ gcc a.c -o a.o1 $ gcc -Wall -Wextra -fno-strict-aliasing -fwrapv -Og -fgcse -fstrict-aliasing a.c -o a.o2 $ gcc -Og -fgcse -fstrict-aliasing a.c -o a.o3 $ ./a.o1 0 $ ./a.o2 -1 $ ./a.o3 -1
prev parent reply other threads:[~2020-10-30 15:28 UTC|newest] Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top 2020-10-19 13:50 [Bug c/97493] New: " suochenyao at 163 dot com 2020-10-19 14:06 ` [Bug c/97493] " jakub at gcc dot gnu.org 2020-10-19 15:23 ` rguenth at gcc dot gnu.org 2020-10-19 15:39 ` jakub at gcc dot gnu.org 2020-10-20 12:59 ` suochenyao at 163 dot com 2020-10-20 12:59 ` suochenyao at 163 dot com 2020-10-30 15:28 ` suochenyao at 163 dot com [this message]
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