Re: swap instruction generation

[naga raj <gnuuser.raj@gmail.com>]

Hi Ian,

   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.

Thanks in Advance,
Nag

On Tue, Apr 19, 2011 at 12:25 AM, Ian Lance Taylor <iant@google.com> wrote:
> naga raj <gnuuser.raj@gmail.com> writes:
>
>>   I need to emit a swap instruction from a embedded target which is
>> using Gcc-4.1.2.
>>
>>   I am trying to emit a instruction which will perform following operation
>>
>>   R0=0x12345678;
>>
>>   swap R1,R0
>>
>>   Then after this R1 should contain R1= 0x00007856;
>
> Not 0x78563421?
>
>>  As there is no bswap rtl expression in Gcc-4.1.2 I have tried various
>> alternatives like:
>>
>>  1. Used rotate rtl expression
>>
>>   2. ashift,ashiftrt and or to generate the above instruction
>>
>>
>>  but compiler is not generating(emitting) swap instruction.
>
> Current gcc has a bswap RTL pattern which swaps bytes in a word.  It was
> added in gcc 4.3.  That's the thing to use if your instruction actually
> swaps bytes in a word.  For versions of gcc before that you will have to
> use an intrinsic function.
>
> Ian
>