This is the mail archive of the mailing list for the GCC project.

Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]
Other format: [Raw text]

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

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.  */
+    && 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;
   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.


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;

John David Anglin

Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]