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Re: [qemu-s390x] [Qemu-devel] [PATCH v1 1/5] s390x/tcg: Implement VECTOR

From: Richard Henderson
Subject: Re: [qemu-s390x] [Qemu-devel] [PATCH v1 1/5] s390x/tcg: Implement VECTOR FIND ANY ELEMENT EQUAL
Date: Wed, 22 May 2019 07:09:53 -0400
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1

On 5/22/19 7:01 AM, David Hildenbrand wrote:
>> I also think that, if we create a bunch more of these wrappers:
>> then RT and ZS can be passed in as constant parameters to the above, and then
>> the compiler will fold away all of the stuff that's not needed for each
>> different case.  Which, I think, is significant.  These are practically
>> different instructions with the different modifiers.
> So, we have 4 flags, resulting in 16 variants. Times 3 element sizes ...
> 48 helpers in total. Do we really want to go down that path?


> I can also go ahead any try to identify the most frequent users (in
> Linux) and only specialize that one.

Also plausible.  I guess it would be good to know, anyway.

I think RT probably makes the largest difference to the layout of the function,
so maybe that's the one we pick.  We could also leave our options open and make
the 3 non-CC flags be parameters to the inline function, just extract them from
the M4 parameter at the one higher level.


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