Hi Ian,
On Wed, Sep 21, 2011 at 6:57 PM, Ian Lance Taylor <iant@xxxxxxxxxx> wrote:
> naga raj <gnuuser.raj@xxxxxxxxx> 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.
>
I have tried with all the possibilities that you have mentioned but
swaph instruction was not generated.
Instead of swaph compiler is generating
1f0: 64640408 bslli r3, r4, 8 (left shift )
1f4: 64840008 bsrli r4, r4, 8 (right shift)
1f8: 80632000 or r3, r3, r4 (or operation)
Thanks,
Nagaraju
