Abt RTL expression - combining instruction

[Rohit Arul Raj]

Hi all,

Finally got the combined compare_and_branch instruction to work. But
it has some side effects while testing other files.

20010129-1.s: Assembler messages:
20010129-1.s:46: Error: Value of 0x88 too large for 7-bit relative
instruction offset

I just designed my compare and branch insn as given below:

(define_insn "compare_and_branch_insn"
   [(set (pc)
        (if_then_else (match_operator 3 "comparison_operator"
                   [(match_operand:SI 1 "register_operand"  "r,r")
                    (match_operand:SI 2 "nonmemory_operand" "O,r")])
                      (label_ref (match_operand 0 "" ""))
                      (pc)))]
""
"*
        output_asm_insn (\"cmp\\t%2, %1\", operands);
/* Body of branch insn */

"
 [(set (attr "length") (if_then_else
                          (ltu
                            (plus
                              (minus
                                (match_dup 0)
                                (pc))
                              (const_int 128))
                            (const_int 250))
                          (const_int 4)
                          (if_then_else
                            (ltu
                              (plus
                                (minus
                                  (match_dup 0)
                                  (pc))
                                (const_int 65536))
                              (const_int 131072))
                            (if_then_else (eq_attr "align_lbranch" "true")
                                          (const_int 6)
                                          (const_int 5))
                            (if_then_else (eq_attr "call_type" "short")
                               (const_int 8)
                               (const_int 16)))))
   (set_attr "delay_type" "delayed")
   (set_attr "type" "compare,branch")]
)

1. Does attribute length affect the calculation of offset?
2. What are the other factors that i have to take into consideration
while combining a compare and branch instruction.

Regards,
Rohit

On 08 Nov 2006 07:00:29 -0800, Ian Lance Taylor <iant@google.com> wrote:
> "Rohit Arul Raj" <rohitarulraj@gmail.com> writes:
>
> > I have used cbranchmode4 instruction to generate combined compare and
> > branch instruction.
> >
> > (define_insn "cbranchmode4"
> >  (set (pc) (if_then_else
> >               (match_operator:CC 0 "comparison_operator"
> >                 [ (match_operand:SI 1  "register_operand"  "r,r")
> >                   (match_operand:SI 2 "nonmemory_operand" "O,r")])
> >               (label_ref (match_operand 3 "" ""))
> >               (pc)))]
> > This pattern matches if the code is of the form
> >
> > if ( h == 1)
> >  p = 0;
> >
> > if the code is of the form
> > if (h), if (h >= 0)
> > p = 0;
> >
> > Then it matches the seperate compare and branch instructions and not
> > cbranch instruction.
> >
> > Can anyone point out where i am going wrong?
>
> If you have a cbranch insn, and you want that one to always be
> recognized, then why do you also have separate compare and branch
> insns?
>
> Ian
>