[Bug tree-optimization/63800] New: ICE on valid code at -O3 on x86_64-linux-gnu

[su at cs dot ucdavis.edu]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63800

            Bug ID: 63800
           Summary: ICE on valid code at -O3 on x86_64-linux-gnu
           Product: gcc
           Version: 5.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: su at cs dot ucdavis.edu

The following code causes an ICE when compiled with the current gcc trunk at
-O3 on x86_64-linux-gnu in both 32-bit and 64-bit modes. 

It is a regression from 4.9.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/5.0.0/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 5.0.0 20141108 (experimental) [trunk revision 217256] (GCC) 

$ gcc-trunk -O2 -c small.c
$ gcc-4.9 -O3 -c small.c
$ 
$ gcc-trunk -O3 -c small.c
small.c: In function ‘fn1’:
small.c:4:1: internal compiler error: Segmentation fault
 fn1 ()
 ^
0xa32bff crash_signal
    ../../gcc-trunk/gcc/toplev.c:358
0xbf5d90 update_dep_bb
    ../../gcc-trunk/gcc/tree-ssa-tail-merge.c:427
0xbf8a68 stmt_update_dep_bb
    ../../gcc-trunk/gcc/tree-ssa-tail-merge.c:457
0xbf8a68 same_succ_hash
    ../../gcc-trunk/gcc/tree-ssa-tail-merge.c:481
0xbf8a68 find_same_succ_bb
    ../../gcc-trunk/gcc/tree-ssa-tail-merge.c:742
0xbf91ac find_same_succ
    ../../gcc-trunk/gcc/tree-ssa-tail-merge.c:773
0xbf91ac init_worklist
    ../../gcc-trunk/gcc/tree-ssa-tail-merge.c:792
0xbf91ac tail_merge_optimize(unsigned int)
    ../../gcc-trunk/gcc/tree-ssa-tail-merge.c:1682
0xbb197f execute
    ../../gcc-trunk/gcc/tree-ssa-pre.c:4831
Please submit a full bug report,
with preprocessed source if appropriate.
Please include the complete backtrace with any bug report.
See <http://gcc.gnu.org/bugs.html> for instructions.
$ 


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


int a, b, c, d[2];

int
fn1 ()
{
  int f = 0;
  d[1] = b = 1; 
  for (; b; b--)
    {
      for (c = 0; c < 2; c++)
    {
      d[b] & 1 & b;
      if (d[0])
        f = d[b] * a;
      if (f)
        return 0;
    }
      d[b] && (d[0] = 0);
    }
  return 0;
}