From: Luke Kenneth Casson Leighton <lkcl@lkcl.net>
Date: Mon, 25 Jul 2022 18:32:29 +0000 (+0100)
Subject: add warm words explaining Scalar part III
X-Git-Tag: opf_rfc_ls005_v1~1031
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=273f688b8a2b04a569b49f42610255d8abb159a0;p=libreriscv.git

add warm words explaining Scalar part III
---

diff --git a/openpower/simple_v_spec.tex b/openpower/simple_v_spec.tex
index f5c4cbb8f..b3fbc12a0 100644
--- a/openpower/simple_v_spec.tex
+++ b/openpower/simple_v_spec.tex
@@ -208,6 +208,7 @@ For questions, comments, and clarification, please contact the following:
 
 \tableofcontents
 
+% Part II
 \part{Scalable Vectors for the Power ISA}
 
 
@@ -268,8 +269,47 @@ For questions, comments, and clarification, please contact the following:
 
 \end{appendices}
 
+% Part III
 \part{Scalar Instructions}
 
+\chapter*{Preamble}{}
+
+As explained in the Simple-V introduction
+these are all intentionally and specifically Scalar instructions.
+They have with almost no exceptions been specifically crafted to
+have a justification for their inclusion in the Power ISA as Scalar
+instructions purely on their own merit.
+
+\begin{itemize}
+	\item The biginteger multiply-and-add instruction is similar
+	to Intel's mulx in that it produces a pair of results.
+	\item Javascript(tm) rounding is present in ARM as fjcvtzs
+	and would save an astounding 35 instructions with 5 branches.
+	\item Whilst there exist CR bit manipulation and copying
+	instructions there are no CR Field maniulation instructions,
+	putting pressure on GPRs if several CR fits need to be analysed.
+\end{itemize}
+
+All of these have nothing to do with Simple-V at all.
+
+That said: by a wonderful coincidence, should they be included, then
+Simple-V's capabilities increase significantly. For example the CRweird
+instructions combined with the bitmanip instructions, alongside 
+Vectorised Rc=1 turn CR Fields into
+extremely powerful Predicate masks.
+
+The clean and clear separation between Vectorisation Prefix and Scalar
+Suffix is what makes it possible for both Scalar-only and Scalable-Vectors
+to benefit.  It also makes proposal much easier, as there is no
+inter-dependence.
+
+It is however important to note that the rationale for these instructions
+comes from a more general-purpose moderen computing paradigm that is
+outside of IBM's much more focussed and specialist traditional customer
+base. We deeply respect IBM's curator role of the Power ISA of the past 25
+years as much as we appreciate their courage in transferring that role
+to the OpenPOWER Foundation ISA Working Group.
+
 \chapter{SV Vector ops}\hypertarget{svux2fvector_ops}{}
 \input{tex_out/vector_ops.tex}
 \chapter{CR Weird ops}\hypertarget{svux2fcr_int_predication}{}
@@ -303,6 +343,7 @@ For questions, comments, and clarification, please contact the following:
 \input{tex_out/pseudocode_svfixedarith.tex}
 \end{appendices}
 
+% Part IV
 \part{Scalar Power ISA pseudocode}
 \backmatter % temporary fix for too many appenfices
 %\setcounter{chapter}{0}