On 6/16/2018 5:53 PM, Farley, Peter x23353 wrote:
The PoP says for the Vector String instructions that "For all instructions that
optionally set the condition code, performance may be degraded if the condition code is
set."
Have you found that performance can be significantly (or at all) improved by
not setting the CC in the SIMD instruction and just always extracting the
seventh byte of operand 1 to see what is the resulting index value in a regular
GR?
GREAT QUESTION! We have not experimented with that yet.
So far, in every case where we expect the cc to be set, we are checking
it right away for example:
DO UNTIL=M
VLL V1,R15,0(R1)
VFEEB V1,V1,V0,M1
DOEXIT 4
AGHI R15,-16
LA R1,16(,R1)
ENDDO ,
Note that the DOEXIT immediately follows the VFEEB.
Despite not seeing such cases in our code, I would speculate that if we
had a situation where we could defer checking of the cc until later (or
not check it at all!), it would make perfect sense to do so.
--
Phoenix Software International
Edward E. Jaffe
831 Parkview Drive North
El Segundo, CA 90245
http://www.phoenixsoftware.com/
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