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Subject: Re: i370 port
To: mutazilah@gmail.com (Paul Edwards)
Date: Mon, 14 Sep 2009 15:42:00 -0000
From: "Ulrich Weigand" <uweigand@de.ibm.com>
Cc: joseph@codesourcery.com (Joseph S. Myers), gcc@gcc.gnu.org
In-Reply-To: <65E668F7450F461E82E66A815F06EEDF@Paullaptop> from "Paul Edwards" at Sep 10, 2009 08:32:30 AM
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Paul Edwards wrote:

> int
> i370_branch_dest (branch)
>      rtx branch;
> {
>   rtx dest = SET_SRC (PATTERN (branch));
>   int dest_uid;
>   int dest_addr;
> 
>   /* first, compute the estimated address of the branch target */
>   if (GET_CODE (dest) == IF_THEN_ELSE)
>     dest = XEXP (dest, 1);
>   dest = XEXP (dest, 0);

This is set up only to handle direct branches of the form

  (set (pc) (label_ref ...))

and indirect branches of the form

  (set (pc) (if_then_else (...) (label_ref ...) (pc)))

but *not* indirect branches of the form

  (set (pc) (if_then_else (...) (pc) (label_ref ...)))

This latter form is accepted by the "negated conditional
jump instructions in the i370.md file, like so:

(define_insn ""
  [(set (pc)
        (if_then_else (eq (cc0)
                          (const_int 0))
                      (pc)
                      (label_ref (match_operand 0 "" ""))))
;   (clobber (reg:SI 14))
   ]
  ""
  "*
{
  check_label_emit ();
  mvs_check_page (0, 4, 0);
  if (i370_short_branch(insn) || mvs_check_label (CODE_LABEL_NUMBER (operands[0])))
    {


Therefore, the i370_branch_dest routine needs to handle
those as well.  Probably something along the following lines:

  if (GET_CODE (dest) == IF_THEN_ELSE)
    {
      if (GET_CODE (XEXP (dest, 1) == LABEL_REF)
	dest = XEXP (dest, 1);
      else
	dest = XEXP (dest, 2);
    }

  gcc_assert (GET_CODE (dest) == LABEL_REF);
  dest = XEXP (dest, 0);

Bye,
Ulrich

-- 
  Dr. Ulrich Weigand
  GNU Toolchain for Linux on System z and Cell BE
  Ulrich.Weigand@de.ibm.com