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From: "su at cs dot ucdavis.edu" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/59387] New: wrong code (hangs) at -Os on x86_64-linux-gnu
Date: Wed, 04 Dec 2013 18:41:00 -0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: new
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X-Bugzilla-Product: gcc
X-Bugzilla-Component: tree-optimization
X-Bugzilla-Version: 4.9.0
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X-Bugzilla-Severity: normal
X-Bugzilla-Who: su at cs dot ucdavis.edu
X-Bugzilla-Status: UNCONFIRMED
X-Bugzilla-Priority: P3
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59387

            Bug ID: 59387
           Summary: wrong code (hangs) at -Os on x86_64-linux-gnu
           Product: gcc
           Version: 4.9.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: su at cs dot ucdavis.edu

The current gcc trunk miscompiles the following code on x86_64-linux at -Os
(but not at the other optimization levels) in both 32-bit and 64-bit modes. 

This is a regression from 4.8.x.

$ gcc-trunk -v
Using built-in specs.
COLLECT_GCC=gcc-trunk
COLLECT_LTO_WRAPPER=/usr/local/gcc-trunk/libexec/gcc/x86_64-unknown-linux-gnu/4.9.0/lto-wrapper
Target: x86_64-unknown-linux-gnu
Configured with: ../gcc-trunk/configure --prefix=/usr/local/gcc-trunk
--enable-languages=c,c++ --disable-werror --enable-multilib
Thread model: posix
gcc version 4.9.0 20131204 (experimental) [trunk revision 205673] (GCC) 
$ 
$ gcc-trunk -O1 small.c; a.out
$ gcc-trunk -O2 small.c; a.out
$ gcc-4.8 -Os small.c; a.out
$ 
$ gcc-trunk -Os small.c
$ a.out
^C
$ 


-------------------------


int a, *d, **e = &d, f;
char c;

struct
{
  int f1;
} b;

int
main ()
{
  for (a = -19; a; a++)
    {
      for (b.f1 = 0; b.f1 < 24; b.f1++)
    c--; 
      *e = &f;
      if (!d)
    return 0;
    }
  return 0;
}