Re: [Qemu-devel] [PATCH 1/8] coccinelle: add a script to optimize tcg op using tcg_gen_extract()

[Eric Blake]

On 05/10/2017 03:19 PM, Richard Henderson wrote:
> On 05/10/2017 01:05 PM, Philippe Mathieu-Daudé wrote:
>> +-tcg_gen_shri_tl(ret, arg, ofs);
>> +-tcg_gen_andi_tl(ret, ret, len);
>> ++tcg_gen_extract_tl(ret, arg, ofs, len);
> 
> You can't simply copy the and mask to the extract length.
> 
> You need to verify it's all low bits and convert that to a count of the
> low bits.  E.g. 0xff -> 8.

Coccinelle may still be able to do that, but it becomes a little less
obvious (and I'm not the expert to consult on what that would look like).

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org

signature.asc
Description: OpenPGP digital signature