Re: [PATCH]: Fix PR middle-end/56382 -- Only move MODE_COMPLEX_FLOAT by parts if we can create pseudos

[John David Anglin <dave dot anglin at bell dot net>]

On 24-Aug-13, at 6:43 AM, Steven Bosscher wrote:

> I'm trying to understand how the patch would help...
>
> The code you're patching is:
>
>  /* Move floating point as parts.  */
>  if (GET_MODE_CLASS (mode) == MODE_COMPLEX_FLOAT
> +    && can_create_pseudo_p ()
>      && optab_handler (mov_optab, GET_MODE_INNER (mode)) !=  
> CODE_FOR_nothing)
>    try_int = false;
>  /* Not possible if the values are inherently not adjacent.  */
>  else if (GET_CODE (x) == CONCAT || GET_CODE (y) == CONCAT)
>    try_int = false;
>  /* Is possible if both are registers (or subregs of registers).  */
>  else if (register_operand (x, mode) && register_operand (y, mode))
>    try_int = true;
>  /* If one of the operands is a memory, and alignment constraints
>     are friendly enough, we may be able to do combined memory  
> operations.
>     We do not attempt this if Y is a constant because that  
> combination is
>     usually better with the by-parts thing below.  */
>  else if ((MEM_P (x) ? !CONSTANT_P (y) : MEM_P (y))
>           && (!STRICT_ALIGNMENT
>               || get_mode_alignment (mode) == BIGGEST_ALIGNMENT))
>    try_int = true;
>  else
>    try_int = false;
>
> With the new test for can_create_pseudo_p, you're trying to make
> "try_int" be false. Apparently your failure happens if one of the
> operands is a MEM? Otherwise the second "else if " test would find x
> and y be registers and "try_int" still ends up being true.

I was trying to prevent "try_int" from being set to false in the "if"  
if we
can't create a pseudo.  If this is done, try_int gets set to true in  
the second
"else if" in the failing testcase.  As a result, we don't directly use
"emit_move_complex_parts" which currently needs a register on hppa64.

> It seems to me that can_create_pseudo_p is not the right test anyway.
> There many be other targets that can take this path just fine without
> needing new registers. In the PR audit trail you say: "The problem is
> SCmode is the same size as DImode on this target, so the subreg can't
> be extracted by a move." Using can_create_pseudo_p is too big a hammer

> to solve this problem. The right test would be to see if you end up
> needing extra registers to perform the move. But emit_move_change_mode
> already handles that, AFAICT, so can you please try and test if the
> following patch solves the PR for you?

I'll give your patch a try.

> Ciao!
> Steven
>
>
> Index: expr.c
> ===================================================================
> --- expr.c      (revision 201887)
> +++ expr.c      (working copy)
> @@ -3268,7 +3268,7 @@ emit_move_complex (enum machine_mode mode, rtx  
> x,
>          return get_last_insn ();
>        }
>
> -      ret = emit_move_via_integer (mode, x, y, true);
> +      ret = emit_move_via_integer (mode, x, y, can_create_pseudo_p  
> ());
>       if (ret)
>        return ret;
>     }


Thanks,
Dave
--
John David Anglin	dave.anglin@bell.net