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Subject: [Bug tree-optimization/48813] New: Segfault with backward branch inside dead loop body
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D48813

           Summary: Segfault with backward branch inside dead loop body
           Product: gcc
           Version: 4.7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: arthur.j.odwyer@gmail.com


Created attachment 24135
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=3D24135
Output of "gcc -Os -funroll-loops -c test227972954.c -v" with gcc 4.4.5

This reproduces for me with svn revision 172950 (2011-04-25), and also with=
 gcc
4.4.5, but strangely not with gcc 4.5.1.  I'm on Ubuntu 10.10, x86-64.

cat >test227972954.c <<EOF
extern unsigned int g_202;
extern int g_16, x;
extern void foo();
int func_103() {
  lbl_240:
    for (g_16 =3D 0; g_16 < 1; ++g_16) {
        foo();
        for (g_202 =3D 4; g_202 <=3D 3; ++g_202) {  /* loop body is dead */
            if (x)
              goto lbl_240;
        }
    }
    return 0;
}
EOF
gcc -Os -funroll-loops -c test227972954.c

test227972954.c: In function =E2=80=98func_103=E2=80=99:
test227972954.c:14:1: internal compiler error: Segmentation fault


gdb's stack trace looks like this:

Program received signal SIGSEGV, Segmentation fault.
0x00000000005aa45c in fix_bb_placements (from=3D0x7ffff6df0820,=20
    irred_invalidated=3D0x7fffffffddfe "") at ../../gcc/cfgloopmanip.c:199
199      SET_BIT (in_queue, base_loop->header->index);
(gdb) backtrace
#0  0x00000000005aa45c in fix_bb_placements (from=3D0x7ffff6df0820,=20
    irred_invalidated=3D0x7fffffffddfe "") at ../../gcc/cfgloopmanip.c:199
#1  0x00000000005aab22 in fix_loop_placements (e=3D<value optimized out>)
    at ../../gcc/cfgloopmanip.c:858
#2  remove_path (e=3D<value optimized out>) at ../../gcc/cfgloopmanip.c:388
#3  0x0000000000745fc6 in peel_loop_completely (flags=3D6)
    at ../../gcc/loop-unroll.c:514
#4  peel_loops_completely (flags=3D6) at ../../gcc/loop-unroll.c:256
#5  unroll_and_peel_loops (flags=3D6) at ../../gcc/loop-unroll.c:165
[...]


This test case is reduced from the output of Csmith
(http://embed.cs.utah.edu/csmith/), using the following command line:
csmith --bitfields --packed-struct -s 227972954 > test227972954.c