From 5031fcff25c8a57718bb86aa35e6618173ff6bba Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Th=C3=A9ophile=20Bastian?= <contact@tobast.fr>
Date: Wed, 10 Apr 2024 17:38:36 +0200
Subject: [PATCH] Frontend: WIP intro writeup
---
manuscrit/40_A72-frontend/00_intro.tex | 7 ++++++-
.../40_A72-frontend/30_manual_frontend.tex | 17 +++++++++++++++--
2 files changed, 21 insertions(+), 3 deletions(-)
diff --git a/manuscrit/40_A72-frontend/00_intro.tex b/manuscrit/40_A72-frontend/00_intro.tex
index e868f19..12edfff 100644
--- a/manuscrit/40_A72-frontend/00_intro.tex
+++ b/manuscrit/40_A72-frontend/00_intro.tex
@@ -37,4 +37,9 @@ very few hardware counters. However, it yielded only mixed results, as shown in
In this chapter, we show that a major cause of imprecision in these results is
the absence of a frontend model. We manually model the Cortex A72 frontend to
compare a raw \palmed{}-generated model, to one naively augmented with a
-frontend model. \todo{discuss automated future work}
+frontend model.
+
+While this chapter only documents a manual approach, we view it as a
+preliminary work towards an automation of the synthesis of a model that stems
+from benchmarks data, in the same way that \palmed{} synthesises a backend
+model.
diff --git a/manuscrit/40_A72-frontend/30_manual_frontend.tex b/manuscrit/40_A72-frontend/30_manual_frontend.tex
index 3a6e867..ed1b721 100644
--- a/manuscrit/40_A72-frontend/30_manual_frontend.tex
+++ b/manuscrit/40_A72-frontend/30_manual_frontend.tex
@@ -2,7 +2,8 @@
\todo{}
-\subsection{Finding micro-operation count for each instruction}
+\subsection{Finding micro-operation count for each
+instruction}\label{ssec:a72_insn_muop_count}
As we saw in \autoref{sec:a72_descr}, the Cortex A72's frontend can only
dispatch three \uops{} per cycle. The first important data to collect, thus, is
@@ -523,4 +524,16 @@ than \llvmmca{} on the Cortex A72.
\section{Future works: benchmark-based automatic frontend model generation}
-\todo{}
+While this chapter was solely centered on the Cortex A72, we believe that this
+study paves the way for an automated frontend model synthesis akin to
+\palmed{}. This synthesis should be fully-automated; stem solely from
+benchmarking data and a description of the ISA; and should avoid the use of any
+specific hardware counter.
+
+The core of the model presented in this chapter is the discovery, for each
+instruction, of its \uop{} count. Assuming that a model of the backend is known
+--~by taking for instance a model generated by \palmed{} or \uopsinfo{}~--, the
+method described in \autoref{ssec:a72_insn_muop_count} should be generic enough
+to be used on any processor. The basic instructions may be easily selected
+using the backend model --~we assume their existence in most
+microarchitectures, as pragmatic concerns guide the ports design. \todo