Re: [PATCH, AARCH64] Fix ICE in CCMP (PR64015)

[Richard Henderson <rth at redhat dot com>]

On 11/25/2014 09:41 AM, Zhenqiang Chen wrote:
> I want to confirm with you two things before I rework it.
> (1) expand_insn needs an optab_handler as input. Do I need to define a ccmp_optab with different mode support in optabs.def?

No, look again: expand_insn needs an enum insn_code as input.  Since this is
the backend, you can use any icode name you like, which means that you can use
CODE_FOR_ccmp_and etc directly.

> (2) To make sure later operands not clobber CC, all operands are expanded before ccmp-first in current implementation. If taking tree/gimple as input, what's your preferred logic to guarantee CC not clobbered?

Hmm.  Perhaps the target hook will need to output two sequences, each of which
will be concatenated while looping around the calls to gen_ccmp_next.  The
first sequence will be operand preparation and the second sequence will be ccmp
generation.

Something like

bool
aarch64_gen_ccmp_start(rtx *prep_seq, rtx *gen_seq,
                       int cmp_code, int bit_code,
                       tree op0, tree op1)
{
  bool success;

  start_sequence ();
  // Widen and expand operands
  *prep_seq = get_insns ();
  end_sequence ();

  start_sequence ();
  // Generate the first compare
  *gen_seq = get_insns ();
  end_sequence ();

  return success;
}

bool
aarch64_gen_ccmp_next(rtx *prep_seq, rtx *gen_seq,
                      rtx prev, int cmp_code, int bit_code,
                      tree op0, tree op1)
{
  bool success;

  push_to_sequence (*prep_seq);
  // Widen and expand operands
  *prep_seq = get_insns ();
  end_sequence ();

  push_to_sequence (*gen_seq);
  // Generate the next ccmp
  *gen_seq = get_insns ();
  end_sequence ();

  return success;
}

If there are ever any failures, the middle-end can simply discard the
sequences.  If everything succeeds, it simply calls emit_insn on both sequences.


r~