[Bug tree-optimization/81192] New: gcc ICE at -Os on x86_64-linux-gnu: Segmentation fault

["helloqirun at gmail dot com" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81192

            Bug ID: 81192
           Summary: gcc ICE at -Os on x86_64-linux-gnu: Segmentation fault
           Product: gcc
           Version: 8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: helloqirun at gmail dot com
  Target Milestone: ---

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


$ gcc-trunk --version
gcc-trunk (GCC) 8.0.0 20170623 (experimental) [trunk revision 249588]


$ gcc-trunk -Os abc.c
during GIMPLE pass: pre
abc.c: In function ‘fn2’:
abc.c:4:6: internal compiler error: Segmentation fault
 void fn2() {
      ^~~
0xc8a4cf crash_signal
        ../../gcc/gcc/toplev.c:338
0xe56285 same_succ_flush_bb
        ../../gcc/gcc/tree-ssa-tail-merge.c:813
0xe580cb same_succ_flush_bbs
        ../../gcc/gcc/tree-ssa-tail-merge.c:828
0xe580cb update_worklist
        ../../gcc/gcc/tree-ssa-tail-merge.c:875
0xe580cb tail_merge_optimize(unsigned int)
        ../../gcc/gcc/tree-ssa-tail-merge.c:1792
0xe06bf0 execute
        ../../gcc/gcc/tree-ssa-pre.c:5162
Please submit a full bug report,
with preprocessed source if appropriate.
Please include the complete backtrace with any bug report.
See <https://gcc.gnu.org/bugs/> for instructions.


$ cat abc.c
unsigned a;
int b, c;
int(fn1)(int p1, int p2) { return p1 > 2147483647 - p2 ? p1 : p1 + p2; }
void fn2() {
  int j;
  a = 30;
  for (; a;)
    for (; c; b = fn1(j, 1))
      ;
}