From: lkcl <lkcl@web>
Date: Wed, 7 Jun 2023 01:56:56 +0000 (+0100)
Subject: (no commit message)
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=04eb3ead5889f539d9cee0ffe2670401beee2304;p=libreriscv.git

---

diff --git a/openpower/sv/po9_encoding/discussion.mdwn b/openpower/sv/po9_encoding/discussion.mdwn
index ce523708a..fa3cbc1ea 100644
--- a/openpower/sv/po9_encoding/discussion.mdwn
+++ b/openpower/sv/po9_encoding/discussion.mdwn
@@ -25,3 +25,14 @@ Length detection:
     else                     return 32
 ```
 
+Instruction allocation restrictions:
+
+* setvl is Unvectorizable but needs more space later: use 55-bit
+* likewise svshape svindex and svshape2, all these need 32-bit
+* svstep *is* Vectorizable but needs to be encoded 32-bit in order
+  to reduce loop-size
+* space for 32-bit instructions is needed: some instructions
+  just make no sense if done as 64-bit because they **replace**
+  two 32-bit instructions.
+* but those types of space-saving instructions
+  **also need to be Vectorizable*