tcg-arm: Use ldrd/strd for appropriate qemu_ld/st64

Reviewed-by: Aurelien Jarno <aurelien@aurel32.net>
Signed-off-by: Richard Henderson <rth@twiddle.net>
tcg-arm: Rearrange slow-path qemu_ld/st

Use the new helper_ret_*_mmu routines.  Use a conditional call
to arrange for a tail-call from the store path, and to load the
return address for the helper for the load path.

Signed-off-by: Richard Henderson <rth@twiddle.net>
tcg-arm: Use strd for tcg_out_arg_reg64

Signed-off-by: Richard Henderson <rth@twiddle.net>
tcg-arm: Use QEMU_BUILD_BUG_ON to verify constraints on tlb

One of the two constraints we already checked via #if, but
the tlb offset distance was only checked at runtime.

Signed-off-by: Richard Henderson <rth@twiddle.net>
tcg-arm: Move load of tlb addend into tcg_out_tlb_read

This allows us to make more intelligent decisions about the relative
offsets of the tlb comparator and the addend, avoiding any need of
writeback addressing.

Signed-off-by: Richard Henderson <rth@twiddle.net>
tcg-arm: Return register containing tlb addend

Preparatory to rescheduling the tlb load, and changing said register.
Continues to use R1 for now.

Signed-off-by: Richard Henderson <rth@twiddle.net>
tcg-arm: Remove restriction on qemu_ld output register

The main intent of the patch is to allow the tlb addend register
to be changed, without tying that change to the constraint.  But
the most common side-effect seems to be to enable usage of ldrd
with the r0,r1 pair.

Signed-off-by: Richard Henderson <rth@twiddle.net>
tcg-arm: Move the tlb addend load earlier

There are free scheduling slots between the sequence of
comparison instructions.  This requires changing the
register in use to avoid conflict with those compares.

Signed-off-by: Richard Henderson <rth@twiddle.net>