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Re: xtensa PR65730


On Fri, Apr 10, 2015 at 9:44 PM, augustine.sterling@gmail.com
<augustine.sterling@gmail.com> wrote:
> On Fri, Apr 10, 2015 at 11:40 AM, augustine.sterling@gmail.com
> <augustine.sterling@gmail.com> wrote:
>>
>> On Fri, Apr 10, 2015 at 11:37 AM, Max Filippov <jcmvbkbc@gmail.com> wrote:
>>>
>>> On Fri, Apr 10, 2015 at 9:29 PM, augustine.sterling@gmail.com
>>> <augustine.sterling@gmail.com> wrote:
>>> > On Fri, Apr 10, 2015 at 6:31 AM, Max Filippov <jcmvbkbc@gmail.com> wrote:
>>> >> OTOH calling helper function to do multiplication by a constant 8 looks
>>> >> rather stupid. I guess we're not going to have non-8-bit bytes on xtensa
>>> >> anytime soon, maybe this multiplication can be replaced with shift?
>>> >
>>> > I think the optimizer will convert it after this point, so it
>>> > shouldn't matter. I would need to verify that though.
>>>
>>> It doesn't, I see the call in the final assembly code, even with various
>>> optimization levels.
>>
>> This is likely a second bug then. It should have been eliminated prior to this call.
>>
>> What happens on a config _with_ a multiply instruction? Do you get a multiply instruction, or a shift?

-O0 gives mull, higher levels give shift.

> Or possibly just a single bug in the sense that the rest of this code
> expects the multiply to be resolved to something else at this point.

Then configuration w/o multiplication should call helper at -O0 and
use shift at higher optimization levels?

-- 
Thanks.
-- Max


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