Hi Faust.
OK. Thanks!
> The BPF backend inline memmove expansion was broken for certain
> constructs. This patch addresses the two underlying issues:
> 1. Off-by-one in the "backwards" unrolled move loop offset.
> 2. Poor use of temporary register for the generated move loop, which
> could result in some of the loads performing the move to be optimized
> away when the source and destination of the memmove are based off of
> the same pointer.
>
> Tested on x86_64-linux-gnu host for bpf-unknown-none target.
> Also tested with Linux kernel bpf selftests, no regressions found.
>
> gcc/
>
> PR target/122140
> * config/bpf/bpf.cc (bpf_expand_cpymem): Fix off-by-one offset
> in backwards loop. Improve src and dest addrs used for the
> branch condition.
> (emit_move_loop): Improve emitted set insns and remove the
> explict temporary register.
>
> ---
> gcc/config/bpf/bpf.cc | 24 +++++++++++-------------
> 1 file changed, 11 insertions(+), 13 deletions(-)
>
> diff --git a/gcc/config/bpf/bpf.cc b/gcc/config/bpf/bpf.cc
> index a28018b3367..39168f689ac 100644
> --- a/gcc/config/bpf/bpf.cc
> +++ b/gcc/config/bpf/bpf.cc
> @@ -1252,13 +1252,11 @@ static void
> emit_move_loop (rtx src, rtx dst, machine_mode mode, int offset, int inc,
> unsigned iters, unsigned remainder)
> {
> - rtx reg = gen_reg_rtx (mode);
> -
> /* First copy in chunks as large as alignment permits. */
> for (unsigned int i = 0; i < iters; i++)
> {
> - emit_move_insn (reg, adjust_address (src, mode, offset));
> - emit_move_insn (adjust_address (dst, mode, offset), reg);
> + emit_insn (gen_rtx_SET (adjust_address (dst, mode, offset),
> + adjust_address (src, mode, offset)));
> offset += inc;
> }
>
> @@ -1266,22 +1264,22 @@ emit_move_loop (rtx src, rtx dst, machine_mode mode,
> int offset, int inc,
> used above. */
> if (remainder & 4)
> {
> - emit_move_insn (reg, adjust_address (src, SImode, offset));
> - emit_move_insn (adjust_address (dst, SImode, offset), reg);
> + emit_insn (gen_rtx_SET (adjust_address (dst, SImode, offset),
> + adjust_address (src, SImode, offset)));
> offset += (inc < 0 ? -4 : 4);
> remainder -= 4;
> }
> if (remainder & 2)
> {
> - emit_move_insn (reg, adjust_address (src, HImode, offset));
> - emit_move_insn (adjust_address (dst, HImode, offset), reg);
> + emit_insn (gen_rtx_SET (adjust_address (dst, HImode, offset),
> + adjust_address (src, HImode, offset)));
> offset += (inc < 0 ? -2 : 2);
> remainder -= 2;
> }
> if (remainder & 1)
> {
> - emit_move_insn (reg, adjust_address (src, QImode, offset));
> - emit_move_insn (adjust_address (dst, QImode, offset), reg);
> + emit_insn (gen_rtx_SET (adjust_address (dst, QImode, offset),
> + adjust_address (src, QImode, offset)));
> }
> }
>
> @@ -1351,13 +1349,13 @@ bpf_expand_cpymem (rtx *operands, bool is_move)
> fwd_label = gen_label_rtx ();
> done_label = gen_label_rtx ();
>
> - rtx dst_addr = copy_to_mode_reg (Pmode, XEXP (dst, 0));
> - rtx src_addr = copy_to_mode_reg (Pmode, XEXP (src, 0));
> + rtx src_addr = force_operand (XEXP (src, 0), NULL_RTX);
> + rtx dst_addr = force_operand (XEXP (dst, 0), NULL_RTX);
> emit_cmp_and_jump_insns (src_addr, dst_addr, GEU, NULL_RTX, Pmode,
> true, fwd_label, profile_probability::even ());
>
> /* Emit the "backwards" unrolled loop. */
> - emit_move_loop (src, dst, mode, size_bytes, -inc, iters, remainder);
> + emit_move_loop (src, dst, mode, (size_bytes - 1), -inc, iters,
> remainder);
> emit_jump_insn (gen_jump (done_label));
> emit_barrier ();
