From db92f902f981bc8bc7aef42965c066605659af87 Mon Sep 17 00:00:00 2001 From: Luke Kenneth Casson Leighton Date: Wed, 25 Sep 2019 09:13:41 +0100 Subject: [PATCH] add note about swapping src1/src2 --- simple_v_extension/appendix.mdwn | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/simple_v_extension/appendix.mdwn b/simple_v_extension/appendix.mdwn index 3c07311f4..8d8941bca 100644 --- a/simple_v_extension/appendix.mdwn +++ b/simple_v_extension/appendix.mdwn @@ -234,6 +234,13 @@ element tests must be performed (and the result optionally stored in the result mask), with a "post-analysis" phase carried out which checks whether to branch. +Note also that whilst it may seem excessive to have all four (because +conditional comparisons may be inverted by swapping src1 and src2), +data-dependent fail-on-first is *not* invertible and *only* terminates +on first zero-condition encountered. Additionally it may be inconvenient +to have to swap the predicate registers associated with src1 and src2, +because this involves a new VBLOCK Context. + ### Standard Branch Branch operations use standard RV opcodes that are reinterpreted to -- 2.30.2