From: lkcl <lkcl@web>
Date: Tue, 14 Jun 2022 06:16:29 +0000 (+0100)
Subject: (no commit message)
X-Git-Tag: opf_rfc_ls005_v1~1798
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=db01d633875631719f949dffc7b695c293e2b853;p=libreriscv.git

---

diff --git a/openpower/sv/mv.swizzle.mdwn b/openpower/sv/mv.swizzle.mdwn
index b1cf79955..26ab13877 100644
--- a/openpower/sv/mv.swizzle.mdwn
+++ b/openpower/sv/mv.swizzle.mdwn
@@ -7,13 +7,16 @@ Links
 * <https://bugs.libre-soc.org/show_bug.cgi?id=139>
 * <https://lists.libre-soc.org/pipermail/libre-soc-dev/2022-June/004913.html>
 
-Swizzle is usually done on a per-operand basis in 3D GPU ISAs, making
-for extremely long instructions (64 bits or greater).
+Swizzle is a type of permute shorthand allowing arbitrary selection
+of elements from vec2/3/4 creating a new vec2/3/4.
 Their value lies in the high occurrence of Swizzle
-in 3D Shader Binaries (over 10% of all instructions),
+in 3D Shader Binaries (over 10% of all instructions).
+Swizzle is usually done on a per-vec-operand basis in 3D GPU ISAs, making
+for extremely long instructions (64 bits or greater),
 however it is not practical to add two or more sets of 12-bit
 prefixes into a single instruction.
-A compromise is to provide a Swizzle "Move".
+A compromise is to provide a Swizzle "Move": one such move is
+then required for each operand to a subsequent instruction.
 The encoding for this instruction embeds static predication into the
 swizzle as well as constants 1/1.0 and 0/0.0