From: lkcl <lkcl@web>
Date: Thu, 9 Jun 2022 12:42:35 +0000 (+0100)
Subject: (no commit message)
X-Git-Tag: opf_rfc_ls005_v1~1898
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=e85a71de680326846b2a06bb61a394ac4815418a;p=libreriscv.git

---

diff --git a/openpower/sv/svp64_quirks.mdwn b/openpower/sv/svp64_quirks.mdwn
index 299d624f2..36c59d594 100644
--- a/openpower/sv/svp64_quirks.mdwn
+++ b/openpower/sv/svp64_quirks.mdwn
@@ -40,7 +40,7 @@ not fundamentally change an add operation into a subtract
 for example, and under absolutely no circumstances do the actual 32-bit
 Scalar v3.0 operand field bits change or the number of operands change.
 
-*(In an early Draft of SVP64,
+In an early Draft of SVP64,
 an experiment was attempted, to modify LD-immediate instructions
 to include a
 third RC register i.e. reinterpret the normal
@@ -53,7 +53,14 @@ to add a 32-bit Scalar Load-with-Shift
 instruction *first*, which then inherently becomes Vectorised.
 Perhaps a future Power ISA spec will have this Load-with-Shift instruction:
 both ARM and x86 have it, because it saves greatly on instruction count in
-hot-loops.)*
+hot-loops.
+
+The other reason for not adding an SVP64-Prefixed instruction without
+also having it as a Scalar un-prefixed instruction is that if the
+32-bit encoding is ever allocated to a completely unrelated operation
+then how can a Vectorised version of that new instruction ever be added?
+Bottom line here is that the fundamental RISC Principle is strictly adhered
+to, even though these are Advanced 64-bit Vector instructions.
 
 # Instruction Groups