https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114591
--- Comment #12 from Hongtao Liu <liuhongt at gcc dot gnu.org> ---
short a;
short c;
short d;
void
foo (short b, short f)
{
c = b + a;
d = f + a;
}
foo(short, short):
addw a(%rip), %di
addw a(%rip), %si
movw %di, c(%rip)
movw %si, d(%rip)
ret
this one is bad since gcc10.1 and there's no subreg, The problem is if the
operand is used by more than 1 insn, and they all support separate m
constraint, mem_cost is quite small(just 1, reg move cost is 2), and this makes
RA more inclined to propagate memory across insns. I guess RA assumes the
separate m means the insn only support memory_operand?
961 if (op_class == NO_REGS)
962 /* Although we don't need insn to reload from
963 memory, still accessing memory is usually more
964 expensive than a register. */
965 pp->mem_cost = frequency;
966 else
