non-normative: add guidance for Zkt alternative sequences

Added a section of alternative sequences that can be built up using Zkt instructions, as requested in today's Tech Chairs.
riscvarchive · Jan 25, 2023 · 4edbea4 · 4edbea4
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diff --git a/header.adoc b/header.adoc
@@ -1,7 +1,7 @@
 [[header]]
 :description: RISC-V Integer Conditional (Zicond) operations extension
 :company: RISC-V.org
-:revdate: 9/2022
+:revdate: 2023-01-25
 :revnumber: 1.0
 :revremark: This document is in development. Assume everything can change. See http://riscv.org/spec-state for details.
 :url-riscv: http://riscv.org

diff --git a/zicondops.adoc b/zicondops.adoc
@@ -128,6 +128,29 @@ or         rd, rd, rtmp
 
 |===
 
+=== Alternative sequences with data-invariant timing
+
+The definition of `czero.eqz` and `czero.nez` does not generally guarantee data-invariant timing (although it guarantees independence of the value of one of its arguments, if the Zkt extension is implemented).
+
+However, sequences using instructions covered by Zkt are available to express the same semantics as for the `czero.eqz` and `czero.nez` instructions:
+
+[%header,cols="2,.^4l"]
+|===
+|Zicond instruction
+|Alternative sequence with data-invariant timing
+
+|`czero.eqz rd, rs1, rs2`
+|snez rtmp, rs2
+neg  rtmp, rtmp
+and  rd, rtmp, rs1
+
+|`czero.nez rd, rs1, rs2`
+|seqz rtmp, rs2
+neg  rtmp, rtmp
+and  rd, rtmp, rs1
+
+|===
+
 == Instructions (in alphabetical order)
 
 <<<