add note about swapping src1/src2

diff --git a/simple_v_extension/appendix.mdwn b/simple_v_extension/appendix.mdwn
index 3c07311f4bc9d1242c11b17a9c208c452acada99..8d8941bcacf93fe752ee72d1653f2b45812f8241 100644 (file)
--- 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 <a name="standard_branch"></a>
 
 Branch operations use standard RV opcodes that are reinterpreted to