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Re: bitrotate
From: |
Simon Josefsson |
Subject: |
Re: bitrotate |
Date: |
Mon, 01 Sep 2008 20:00:49 +0200 |
User-agent: |
Gnus/5.110011 (No Gnus v0.11) Emacs/22.2 (gnu/linux) |
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
- Re: bitrotate, Simon Josefsson, 2008/09/01
- Re: bitrotate, Paolo Bonzini, 2008/09/01
- Re: bitrotate,
Simon Josefsson <=
- Re: bitrotate, Bruno Haible, 2008/09/01
- Re: bitrotate, Simon Josefsson, 2008/09/01
- Re: bitrotate, Simon Josefsson, 2008/09/01
- Re: bitrotate, Ben Pfaff, 2008/09/01
- Re: bitrotate, Bruno Haible, 2008/09/01
- Re: bitrotate, Simon Josefsson, 2008/09/02
- Re: bitrotate, Eric Blake, 2008/09/02
- Re: bitrotate, Simon Josefsson, 2008/09/02