Re: bitrotate

[Simon Josefsson]

Paolo Bonzini <address@hidden> writes:

>> I suspect the rotation part is the sarl+sall and or.  Either we could
>> experiment with changing the code, or we could try to make gcc detect
>> that this code actually is a rotate...  Possibly gcc already does that
>> right thing, with today's CPU architectures it can be difficult to know
>> which ops are the most efficient choice.
>
> I don't know, GCC already has plenty of rotate-detection code.  It might
> be that for 16-bit it does not like to give a rotate to your machine.
> Usually, trying with -mtune=i386 is a way to see if it has taken its
> decision based on the hardware.

I checked with 32-bit rotates, and then I do see it use the proper
instructions.  Couldn't get it to use them for 16-bit rotates though.  I
don't have more energy to investigate it though.

/Simon