https://gcc.gnu.org/bugzilla/show_bug.cgi?id=128620
--- Comment #3 from Tobias Burnus <burnus at gcc dot gnu.org> ---
The problem is in
Breakpoint 3, validate_subreg (omode=omode@entry=E_QImode, imode=E_HImode,
reg=reg@entry=0x7ffff6c80cf0, offset=...) at […]/gcc/emit-rtl.cc:925
for:
992 /* Ensure that subregs of hard registers can be folded. In other
words,
993 the hardware register must be valid in the subreg's outer mode,
994 and consequently the subreg can be replaced with a hardware
register. */
995 if (reg && REG_P (reg) && HARD_REGISTER_P (reg))
996 {
997 unsigned int regno = REGNO (reg);
998
999 if ((COMPLEX_MODE_P (imode) || VECTOR_MODE_P (imode))
1000 && GET_MODE_INNER (imode) == omode)
1001 ;
1002 else if (!REG_CAN_CHANGE_MODE_P (regno, imode, omode))
1003 return false;
at
#0 validate_subreg (omode=omode@entry=E_QImode, imode=<optimized out>,
reg=reg@entry=0x7ffff6c80cf0, offset=...) at
/net/vbuild-02/srv/data/tburnus/repos/gcc/gcc/emit-rtl.cc:1002
1002 else if (!REG_CAN_CHANGE_MODE_P (regno, imode, omode))
(gdb) p omode
$11 = E_QImode
(gdb) p regno
$12 = 0
(gdb) p imode
$10 = <optimized out>
which can be determined via:
1062 gcc_assert (validate_subreg (mode, GET_MODE (reg), reg, offset));
(gdb) p debug(reg)
(reg:HI 0 %value)
$13 = void
