Describe Top level binding inlining.

[matthijs/master-project/report.git] / Chapters / Normalization.tex

diff --git a/Chapters/Normalization.tex b/Chapters/Normalization.tex
index f1b53dfa7bc681969763e478045cec681ca62b09..89c2d4a13faafd1ac6df231082632d1d78777148 100644 (file)
--- a/Chapters/Normalization.tex
+++ b/Chapters/Normalization.tex
@@ -862,8 +862,50 @@
         Since its exact role and need is not clear yet, this transformation is
         not yet specified.
 
-      \subsubsection{Compiler generated top level binding inlining}
-        TODO
+      \subsubsection{Top level binding inlining}
+        This transform takes simple top level bindings generated by the
+        \small{GHC} compiler. \small{GHC} sometimes generates very simple
+        \quote{wrapper} bindings, which are bound to just a variable
+        reference, or a partial application to constants or other variable
+        references.
+
+        Note that this transformation is completely optional. It is not
+        required to get any function into normal form, but it does help making
+        the resulting VHDL output easier to read (since it removes a bunch of
+        components that are really boring).
+
+        This transform takes any top level binding generated by the compiler,
+        whose normalized form contains only a single let binding.
+
+        \starttrans
+        x = λa0 ... λan.let y = E in y
+        ~
+        x
+        --------------------------------------         \lam{x} is generated by the compiler
+        λa0 ... λan.let y = E in y
+        \stoptrans
+
+        \startbuffer[from]
+        (+) :: Word -> Word -> Word
+        (+) = GHC.Num.(+) @Word $dNum
+        ~
+        (+) a b
+        \stopbuffer
+        \startbuffer[to]
+        GHC.Num.(+) @ Alu.Word $dNum a b
+        \stopbuffer
+
+        \transexample{Top level binding inlining}{from}{to}
+       
+        Without this transformation, the (+) function would generate an
+        architecture which would just add its inputs. This generates a lot of
+        overhead in the VHDL, which is particularly annoying when browsing the
+        generated RTL schematic (especially since + is not allowed in VHDL
+        architecture names\footnote{Technically, it is allowed when using
+        extended identifiers, but it seems that none of the tooling likes
+        extended identifiers in filenames, so it effectively doesn't work}, so
+        the entity would be called \quote{w7aA7f} or something similarly
+        unreadable and autogenerated).
 
     \subsection{Program structure}
       These transformations are aimed at normalizing the overall structure