[Bug target/128440] [14/15/16/17 Regression] BPF incorrectly expands backwards memmove

[mateuszb at poczta dot onet.pl via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=128440

mateuszb at poczta dot onet.pl changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |mateuszb at poczta dot onet.pl

--- Comment #8 from mateuszb at poczta dot onet.pl ---
For the move "backwards" starting from SRC + SIZE we must start from the last
byte of "remainder" bytes and finish with copy in chunks as large as alignment
permits in "backwards" order.

1) code:
      /* Emit the "backwards" unrolled loop.  */
      emit_move_loop (src, dst, mode, (size_bytes - inc), -inc, iters,
remainder);
should be replaced by:
      /* Emit the "backwards" unrolled loop.  */
      emit_move_loop (src, dst, mode, size_bytes, -inc, iters, remainder);

2) in:
static void
emit_move_loop (rtx src, rtx dst, machine_mode mode, int offset, int inc,
                unsigned iters, unsigned remainder)

for memmove "backwards" (inc < 0) we should start with:
  if (remainder & 1)
    {
      offset -= 1;
      remainder -= 1;
      emit_insn (gen_rtx_SET (adjust_address (dst, QImode, offset),
                              adjust_address (src, QImode, offset)));
    }

and so on for 2 and 4 until:

  for (unsigned int i = 0; i < iters; i++)
    {
      offset += inc;
      emit_insn (gen_rtx_SET (adjust_address (dst, mode, offset),
                              adjust_address (src, mode, offset)));
    }