Re: [PATCH 4/7] ifcvt/optabs: Allow using a CC comparison for emit_conditional_move.

[Richard Sandiford <richard.sandiford@arm.com>]

> Before, we had a loop with two iterations that tried "emit_cmov (cond, 
> op2, op3)".  op2 and op3 can (or even were) If this did not succeed we 
> would revert the condition as well as op3 and op3 in-place and try 
> again.  I found that a bit cumbersome and intended to make this explicit 
> but it's still kind of involved, particularly since cond may come in 
> reversed, we additionally swap op2 and op3 and all the way back again.
>
> I remember from the first iteration of these patches that this (double 
> revert) was needed for exactly one test case in the test suite on x86. 
> When re-running it today I could not reproduce it anymore, though.

Hmm, OK.  Doesn't expanding both versions up-front create the same kind of
problem that the patch is fixing, in that we expand (and therefore cost)
both the reversed and unreversed comparison?  Also…

Robin Dapp <rdapp@linux.ibm.com> writes:
> @@ -4782,17 +4784,30 @@ emit_conditional_move (rtx target, enum rtx_code code, rtx op0, rtx op1,
>    if (cmode == VOIDmode)
>      cmode = GET_MODE (op0);
>  
> -  enum rtx_code orig_code = code;
> +  /* If the first condition operand is constant and the second is not, swap
> +     them.  In that case we also need to reverse the comparison.
> +     If both are non-constant It is possible that the conditional move
> +     will not expand with operands in this order, e.g. when we are about to
> +     create a min/max expression and the operands do not match the condition.
> +     In that case we also need the reversed condition code and comparison.  */

…for min/max, I would have expected this swap to create the canonical
operand order for the min and max too.  What causes it to be rejected?

> +
> +  rtx rev_comparison = NULL_RTX;
>    bool swapped = false;
> -  if (swap_commutative_operands_p (op2, op3)
> -      && ((reversed = reversed_comparison_code_parts (code, op0, op1, NULL))
> -          != UNKNOWN))
> +
> +  code = unsignedp ? unsigned_condition (code) : code;
> +  comparison = simplify_gen_relational (code, VOIDmode, cmode, op0, op1);
> +
> +  if ((reversed = reversed_comparison_code_parts (code, op0, op1, NULL))
> +      != UNKNOWN)
>      {
> -      std::swap (op2, op3);
> -      code = reversed;
> -      swapped = true;
> +      reversed = unsignedp ? unsigned_condition (reversed) : reversed;

When is this needed?  I'd have expected the reversed from of an unsigned
code to be naturally unsigned.

Thanks,
Richard

> +      rev_comparison = simplify_gen_relational (reversed, VOIDmode, cmode,
> +						op0, op1);
>      }
>  
> +  if (swap_commutative_operands_p (op2, op3) && reversed != UNKNOWN)
> +    swapped = true;
> +
>    if (mode == VOIDmode)
>      mode = GET_MODE (op2);
>  
> @@ -4804,58 +4819,99 @@ emit_conditional_move (rtx target, enum rtx_code code, rtx op0, rtx op1,
>    if (!target)
>      target = gen_reg_rtx (mode);
>  
> -  for (int pass = 0; ; pass++)
> +  if (comparison && COMPARISON_P (comparison))
> +    prepare_cmp_insn (XEXP (comparison, 0), XEXP (comparison, 1),
> +		      GET_CODE (comparison), NULL_RTX,
> +		      unsignedp, OPTAB_WIDEN, &comparison, &cmode);
> +  else
> +    return NULL_RTX;
> +
> +  if (rev_comparison && COMPARISON_P (rev_comparison))
> +    prepare_cmp_insn (XEXP (rev_comparison, 0), XEXP (rev_comparison, 1),
> +		      GET_CODE (rev_comparison), NULL_RTX,
> +		      unsignedp, OPTAB_WIDEN, &rev_comparison, &cmode);
> +
> +  if (!swapped)
> +    return emit_conditional_move (target, comparison, rev_comparison,
> +				  op2, op3, mode);
> +  else
> +    return emit_conditional_move (target, rev_comparison, comparison,
> +				  op3, op2, mode);
> +}
> +
> +/* Helper function for emitting a conditional move.  Given a COMPARISON
> +   and a reversed REV_COMPARISON it will try to expand a conditional move
> +   with COMPARISON first and try with REV_COMPARISON if that fails.  */
> +
> +rtx
> +emit_conditional_move (rtx target, rtx comparison, rtx rev_comparison,
> +		       rtx op2, rtx op3, machine_mode mode)
> +{
> +
> +  rtx res = emit_conditional_move (target, comparison, op2, op3, mode);
> +
> +  if (res != NULL_RTX)
> +    return res;
> +
> +  return emit_conditional_move (target, rev_comparison, op3, op2, mode);
> +}
> +
> +/* Helper for emitting a conditional move.  */
> +
> +static rtx
> +emit_conditional_move (rtx target, rtx comparison,
> +		       rtx op2, rtx op3, machine_mode mode)
> +{
> +  rtx_insn *last;
> +  enum insn_code icode;
> +
> +  if (comparison == NULL_RTX || !COMPARISON_P (comparison))
> +    return NULL_RTX;
> +
> +  /* If the two source operands are identical, that's just a move.  */
> +  if (rtx_equal_p (op2, op3))
>      {
> -      code = unsignedp ? unsigned_condition (code) : code;
> -      comparison = simplify_gen_relational (code, VOIDmode, cmode, op0, op1);
> +      if (!target)
> +	target = gen_reg_rtx (mode);
>  
> -      /* We can get const0_rtx or const_true_rtx in some circumstances.  Just
> -	 punt and let the caller figure out how best to deal with this
> -	 situation.  */
> -      if (COMPARISON_P (comparison))
> -	{
> -	  saved_pending_stack_adjust save;
> -	  save_pending_stack_adjust (&save);
> -	  last = get_last_insn ();
> -	  do_pending_stack_adjust ();
> -	  machine_mode cmpmode = cmode;
> -	  prepare_cmp_insn (XEXP (comparison, 0), XEXP (comparison, 1),
> -			    GET_CODE (comparison), NULL_RTX, unsignedp,
> -			    OPTAB_WIDEN, &comparison, &cmpmode);
> -	  if (comparison)
> -	    {
> -	      class expand_operand ops[4];
> +      emit_move_insn (target, op3);
> +      return target;
> +    }
>  
> -	      create_output_operand (&ops[0], target, mode);
> -	      create_fixed_operand (&ops[1], comparison);
> -	      create_input_operand (&ops[2], op2, mode);
> -	      create_input_operand (&ops[3], op3, mode);
> -	      if (maybe_expand_insn (icode, 4, ops))
> -		{
> -		  if (ops[0].value != target)
> -		    convert_move (target, ops[0].value, false);
> -		  return target;
> -		}
> -	    }
> -	  delete_insns_since (last);
> -	  restore_pending_stack_adjust (&save);
> -	}
> +  if (mode == VOIDmode)
> +    mode = GET_MODE (op2);
>  
> -      if (pass == 1)
> -	return NULL_RTX;
> +  icode = direct_optab_handler (movcc_optab, mode);
>  
> -      /* If the preferred op2/op3 order is not usable, retry with other
> -	 operand order, perhaps it will expand successfully.  */
> -      if (swapped)
> -	code = orig_code;
> -      else if ((reversed = reversed_comparison_code_parts (orig_code, op0, op1,
> -							   NULL))
> -	       != UNKNOWN)
> -	code = reversed;
> -      else
> -	return NULL_RTX;
> -      std::swap (op2, op3);
> +  if (icode == CODE_FOR_nothing)
> +    return NULL_RTX;
> +
> +  if (!target)
> +    target = gen_reg_rtx (mode);
> +
> +  saved_pending_stack_adjust save;
> +  save_pending_stack_adjust (&save);
> +  last = get_last_insn ();
> +  do_pending_stack_adjust ();
> +
> +  class expand_operand ops[4];
> +
> +  create_output_operand (&ops[0], target, mode);
> +  create_fixed_operand (&ops[1], comparison);
> +  create_input_operand (&ops[2], op2, mode);
> +  create_input_operand (&ops[3], op3, mode);
> +
> +  if (maybe_expand_insn (icode, 4, ops))
> +    {
> +      if (ops[0].value != target)
> +	convert_move (target, ops[0].value, false);
> +      return target;
>      }
> +
> +  delete_insns_since (last);
> +  restore_pending_stack_adjust (&save);
> +
> +  return NULL_RTX;
>  }
>  
>  
> diff --git a/gcc/optabs.h b/gcc/optabs.h
> index 3bbceff92d9..f853b93f37f 100644
> --- a/gcc/optabs.h
> +++ b/gcc/optabs.h
> @@ -281,6 +281,7 @@ extern void emit_indirect_jump (rtx);
>  /* Emit a conditional move operation.  */
>  rtx emit_conditional_move (rtx, enum rtx_code, rtx, rtx, machine_mode,
>  			   rtx, rtx, machine_mode, int);
> +rtx emit_conditional_move (rtx, rtx, rtx, rtx, rtx, machine_mode);
>  
>  /* Emit a conditional negate or bitwise complement operation.  */
>  rtx emit_conditional_neg_or_complement (rtx, rtx_code, machine_mode, rtx,