swap instruction generation

[Ian Lance Taylor]

naga raj <gnuuser.raj@gmail.com> writes:

>    I am using Gcc-4.6.0 and I have used bswap RTL pattern for both SI
> and HI modes to generate swapb & swaph instructions respectively.
>
>   (define_insn "bswapsi2"
>   [(set (match_operand:SI 0 "register_operand" "=r")
>         (bswap:SI (match_operand:SI 1 "register_operand" "r")))]
>   ""
>   "swapb %0, %1"
> )
>
> (define_insn "bswaphi2"
>   [(set (match_operand:HI           0 "register_operand" "=r")
>         (bswap:HI (match_operand:HI 1 "register_operand"  "r")))]
>   ""
>   "swaph %0, %1"
> )
>
>
>
> I have written a sample example to generate these instructions..
> int swapb(int n)
> {
>   return ((((n) & 0xff000000) >> 24)
>             | (((n) & 0x00ff0000) >>  8)
>             | (((n) & 0x0000ff00) <<  8)
>             | (((n) & 0x000000ff) << 24));
>
> }
> short int swaph(short int n)
> {
> return  ((((n) & 0xff00) >>  8)
>             | (((n) & 0xff) <<  8));
> }
> int main()
> {
>   volatile int a=0x12345678;
>    volatile short int b=0x1234;
>   a=swapb(a);
>   b=swaph(b);
>  return 0;
> }
>
> with this example "swapb" instruction has generated but I am unable to
> generate "swaph"(HI mode of bswap RTL pattern) instruction
>
> I have tried all possibilities that I know.
> Am I missing something or this approach is wrong.
> Please guide me to generate swaph instruction.

I'm surprised that you even get swapb when using a volatile variable.  I
would remove the volatile.  Just make them global variables or function
arguments or something.

Also you should make b an unsigned short, so that gcc doesn't have to
worry about sign extending the result when the expression is implicitly
calculated in type int.

Good luck.

Ian