From: lkcl Date: Mon, 26 Oct 2020 21:13:41 +0000 (+0000) Subject: (no commit message) X-Git-Tag: convert-csv-opcode-to-binary~1930 X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=941f786040081a44f95dd965942bc2534f8dcada;p=libreriscv.git --- diff --git a/openpower/sv/predication.mdwn b/openpower/sv/predication.mdwn index becd0468d..9e5c2f04e 100644 --- a/openpower/sv/predication.mdwn +++ b/openpower/sv/predication.mdwn @@ -43,9 +43,11 @@ As well-known weaknesses that compromise performance, very little use of OE=1 is One of the design principles of SV is that the use of VL should be as closrly equivalent to a direct substitution of the scalar operations of the hardware for-loop as possible, as if those looped operations were actually in the instruction stream rather than being issued from the Vector loop. -The implications here are that **register dependency hazards still have to be respected inter-element**. +The implications here are that *register dependency hazards still have to be respected inter-element*. -Using a multi-issue out-of-order engine as the underlying microarchitectural basis this is not as difficult to achieve as it first seems. In addition, Vectir Chaining should also be possible for a multi-issue out-of-order rngine to cope with, as long as false (unnecessary) Dependency Hazards are not introduced. +Using a multi-issue out-of-order engine as the underlying microarchitectural basis this is not as difficult to achieve as it first seems. In addition, Vector Chaining should also be possible for a multi-issue out-of-order rngine to cope with, as long as false (unnecessary) Dependency Hazards are not introduced in between Vectors, where the dependencies actually only exist between elements *in* the Vector. + +The concept of recognising that it is the elements within the Vector that have Dependency Hazards rather than the Vectors themselves is what permits Cray-style "chaining". This "false/unnecessary hazard" condition eliminates and/or compromises the performance or drives up resource utilisation in at least two of the proposals below.