https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68991
--- Comment #14 from H.J. Lu <hjl.tools at gmail dot com> ---
(In reply to H.J. Lu from comment #13)
> > LRA is OK when Bm is properly defined as
> >
> > (define_memory_constraint "Bm"
> > "@internal Vector memory operand."
> > (match_operand 0 "vector_memory_operand"))
>
> It doesn't work since process_alt_operands in LRA will treat Bm as m:
>
> case CT_MEMORY:
> if (MEM_P (op)
> && satisfies_memory_constraint_p (op, cn))
> win = true;
> else if (spilled_pseudo_p (op))
> win = true;
>
> and ignores vector_memory_operand.
It happens with
case CT_MEMORY:
if (MEM_P (op)
&& satisfies_memory_constraint_p (op, cn))
win = true;
else if (spilled_pseudo_p (op))
win = true;
/* If we didn't already win, we can reload constants
via force_const_mem or put the pseudo value into
memory, or make other memory by reloading the
address like for 'o'. */
if (CONST_POOL_OK_P (mode, op)
|| MEM_P (op) || REG_P (op))
badop = false;
/* If this operand accepts a register, and if the
register class has at least one allocatable register,
then this operand can be reloaded. */
if (winreg && !no_regs_p)
badop = false;
