https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63502
--- Comment #1 from Bill Klees <bill.klees at teamquest dot com> --- Setting breakpoint at s390_add_constant Breakpoint 5, s390_add_constant (pool=0x80da0880, val=0x20003889cc0, mode=BLKmod at /home/bjk/gcc/gcc-4.9.1/./gcc/config/s390/s390.c:6400 6400 for (i = 0; i < NR_C_MODES; i++) (gdb) list 6395 s390_add_constant (struct constant_pool *pool, rtx val, enum machine_mode mode) 6396 { 6397 struct constant *c; 6398 int i; 6399 6400 for (i = 0; i < NR_C_MODES; i++) 6401 if (constant_modes[i] == mode) 6402 break; 6403 gcc_assert (i != NR_C_MODES); 6404 (gdb) print constant_modes $4 = {TFmode, TImode, TDmode, DFmode, DImode, DDmode, SFmode, SImode, SDmode, HImode, QImode} (gdb) print mode $5 = BLKmode (gdb) Failure occurs on the assert since BLKmode is not in the list.