Add Linkage section (#249)

Add Linkage section
Add empty chapter file for Statements to preserve the chapter ordering

specs/language/declarations.tex

@@ -0,0 +1,46 @@
+\Ch{Declarations}{Decl}
+\Sec{Function Definitions}{Decl.Function}
+\Sec{Attributes}{Decl.Attr}
+\Sub{Entry Attributes}{Decl.Attr.Entry}
+\Sec{Linkage}{Decl.Linkage}
+
+\p An entity that denotes an object, reference, function, type, template, namespace, or value, may have a \textit{linkage}. If a name has \textit{linkage}, it refers to the same entity as the same name introduced by a declaration in another scope. If a variable, function, or another entity with the same name is declared in several scopes, but does not have sufficient \textit{linkage}, then several instances of the entity are generated.
+
+\p There are three linkages recognized: \textit{external linkage}, \textit{internal linkage} and \textit{no linkage}.
+
+\Sub{External Linkage}{Decl.Linkage.External}
+
+\p Entities with \textit{external linkage} can be referred to from the scopes in the other translation units and enable linking between them.
+
+\p The following entities in HLSL have \textit{external linkage}:
+\begin{itemize}
+  \item entry point functions
+  \item functions marked with \texttt{export} keyword
+  \item global variables that are not marked \texttt{static} or \texttt{groupshared} \footnote{These are not really linked with other translation units but rather their values are loaded indirectly based on cbuffer mapping.}
+  \item static data members of classes or template classes
+\end{itemize}
+
+\p Linkage of functions (including template functions) that are not entry points or marked with \texttt{export} keyword is implementation dependent. \footnote{In DXC today functions that are not entry points or exported have \textit{internal linkage} by default. This can be overriden by \texttt{-default-linkage} compiler option.}
+
+\Sub{Internal Linkage}{Decl.Linkage.Internal}
+
+\p Entities with \textit{internal linkage} can be referred to from all scopes in the current translation unit.
+
+\p The following entities in HLSL have \textit{internal linkage}:
+\begin{itemize}
+  \item global variables marked as \texttt{static} or \texttt{groupshared}
+  \item all entities declared in an unnamed namespace or a namespace within an unnamed namespace
+  \item enumerations
+  \item classes or template classes, their member functions, and nested classes and enumerations
+\end{itemize}
+
+\Sub{No Linkage}{Decl.Linkage.NoLinkage}
+
+\p An entity with \textit{no linkage} can be referred to only from the scope it is in.
+
+\p Any of the following entites declared at function scope or block scopes derived from function scope have no linkage:
+\begin{itemize}
+  \item local variables
+  \item local classes and their member functions
+  \item other entities declared at function scope or block scopes derived from function scope that such as typedefs, enumerations, and enumerators
+\end{itemize}

specs/language/hlsl.tex

@@ -89,6 +89,8 @@
 \input{conversions}
 \input{expressions}
 \input{overloading}
+\input{statements}
+\input{declarations}
 
 \input{placeholders} % Declare placeholder references
 

specs/language/placeholders.tex

@@ -4,12 +4,6 @@
 % forward references can be inserted into the specification as it is being
 % written to force updating the references as they change.
 
-\Ch{Statements}{Stmt}
-\Sec{Label Statements}{Stmt.Label}
-\Ch{Declarations}{Decl}
-\Sec{Function Definitions}{Decl.Function}
-\Sec{Attributes}{Decl.Attr}
-\Sub{Entry Attributes}{Decl.Attr.Entry}
 \Ch{Classes}{Classes}
 \Sec{Static Members}{Classes.Static}
 \Sec{Conversions}{Classes.Conversions}

specs/language/statements.tex

@@ -0,0 +1,2 @@
+\Ch{Statements}{Stmt}
+\Sec{Label Statements}{Stmt.Label}