bit test instruction

[Jeff Law]

On 01/21/15 19:35, James Bowman wrote:
> My target has a bit test (btst) instruction, so the C code:
>
>    if (x & 256)
>
> can be efficiently coded as (for example):
>
>    btst    $r0,256
>    jmp    nz,.L1
>
> However, with my current patterns, it generates an explicit "and" and
> "compare" using a scratch:
>
>    and    $r1,$r0,256
>    cmp   $r1,0
>    jmp    nz,.L1
>
> Looking through targets with a similar instruction - arc, rx, s390,
> i386 - I see several different approaches. They all seem quite
> complicated.
>
> What is the best way of implementing this? Thanks.


PA also has a bit test, both constant and variable position.

(define_insn ""
   [(set (pc)
         (if_then_else
          (ne (zero_extract:SI (match_operand:SI 0 "register_operand" "r")
                               (const_int 1)
                               (match_operand:SI 1 "uint5_operand" ""))
              (const_int 0))
          (label_ref (match_operand 2 "" ""))
          (pc)))]


That's the constant position test.  There's a similar pattern for 
testing at a variable position.



jeff