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[Lang] Update and restructure cbuffer spec (#684)
This change pulls the cbuffer section into the Declarations chapter instead of the Resources chapter since it defines a declaration type, and updates the grammar and specification language based on the updates to proposal 37. The updated language avoids nesting of cbuffers and namepaces in cbuffers to simplify semantic validation. The updated langauge also adds additional language around storage durations which is referenced in the updated specification language. Resolves #671 --------- Co-authored-by: Helena Kotas <hekotas@microsoft.com>
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‎specs/language/basic.tex‎

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\Sec{Name Lookup}{Basic.Lookup}
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\Sec{Storage Duration}{Basic.Storage}
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\p The storage duration of an object is the portion of the program's execution
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time during which the object exists in memory. An object may have one of the
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following storage durations:
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\begin{itemize}
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\item \textit{static storage duration}
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\item \textit{automatic storage duration}
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\item \textit{program storage duration}
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\item \textit{groupshared storage duration}
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\end{itemize}
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\Sub{Static Storage Duration}{Basic.Storage.Static}
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\p An object whose name is declared with the \texttt{static} storage specifier
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has \textit{static storage duration}. Such an object is created when the thread
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begins execution and destroyed when the thread ends execution.
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\Sub{Automatic Storage Duration}{Basic.Storage.Auto}
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\p An object whose name is declared in a block (including function parameters)
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without the \texttt{static} storage specifier has \textit{automatic storage
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duration}. Such an object is created when the block in which it is declared is
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entered and destroyed when the block is exited.
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\Sub{Program Storage Duration}{Basic.Storage.Program}
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\p An object whose name is declared in a global, namespace, or cbuffer scope
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without the \texttt{static} storage specifier has \textit{program storage
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duration}. Such an object is created when the program begins execution and
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destroyed when the program ends execution.
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\Sub{Groupshared Storage Duration}{Basic.Storage.Groupshared}
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\p An object whose name is declared with the \texttt{groupshared} storage
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specifier has \textit{groupshared storage duration}. Such an object is created
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when the thread group begins execution and destroyed when the thread group ends.
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\Sec{Program and linkage}{Basic.Linkage}
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\p A translation unit (\ref{Lex.Translation}) is comprised of a sequence of

‎specs/language/declarations.tex‎

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\p Declarations generally specify how names are to be interpreted. Declarations have the form
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\begin{grammar}
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\define{declaration-seq}\br
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\textit{declaration}\br
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\textit{declaration-seq declaration}
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declaration\br
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declaration-seq declaration\br
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\define{declaration}\br
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\textit{name-declaration}\br
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\textit{special-declaration}\br
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\textit{empty-declaration}
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name-declaration\br
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special-declaration\br
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\define{name-declaration}\br
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\textit{variable-declaration}\br
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\textit{function-declaration}\br
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\textit{namespace-declaration}\br
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\textit{record-declaration}\br
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\textit{template-declaration}\br
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\textit{type-alias-declaration}\br
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...
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block-declaration\br
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function-definition\br
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template-declaration\br
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namespace-definition\br
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empty-declaration\br
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attribute-declaration\br
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cbuffer-declaration\br
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\define{special-declaration}\br
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\textit{export-declaration-group}\br
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\textit{cbuffer-declaration-group}\br
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...
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export-declaration-group\br
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cbuffer-member-declaration\br
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\define{block-declaration}\br
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simple-declaration\br
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namespace-alias-definition\br
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using-declaration\br
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using-directive\br
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static\_assert-declaration\br
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alias-declaration\br
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opaque-enum-declaration\br
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\define{empty-declaration}\br
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\terminal{;}
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\define{empty-declaration} \terminal{;}
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\end{grammar}
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\Sec{Specifiers}{Decl.Spec}
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\p Functions with \textit{external linkage} can also be declared with an \texttt{export} specifier (\ref{Decl.Spec.Fct}).
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\p If a function is part of an \textit{export-declaration-group} then all redeclarations of the same function must also be part on a \textit{export-declaration-group} or be declared with an \texttt{export} specifier (\ref{Decl.Spec.Fct}).
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\Sec{Constant Buffer Declarations}{Decl.cbuffer}
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\begin{grammar}
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\define{cbuffer-declaration}\br
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\terminal{cbuffer} name \opt{resource-binding} \terminal{\{}
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\opt{cbuffer-member-seq} \terminal {\}}\br
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\define{cbuffer-member-seq}\br
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cbuffer-member-declaration\br
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cbuffer-member-seq cbuffer-member-declaration\br
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\define{cbuffer-member-declaration}\br
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block-declaration\br
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function-definition\br
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template-declaration\br
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empty-declaration
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\end{grammar}
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\p A \textit{cbuffer declaration} is declared with the \texttt{cbuffer} keyword.
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The name of the cbuffer declaration does not declare a name, and cannot be
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referenced from within the translation unit, nor is it required to be unique.
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Each cbuffer declaration refers to a unique constant buffer resource
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(\ref{Resources.cnbuf}).
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\p The cbuffer declaration itself does not declare a declaration scope.
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Declarations within a cbuffer declaration that declare names, declare their names
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in the scope containing the cbuffer declaration. A cbuffer declaration may not
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contain a \textit{namespace-declaration} or \textit{cbuffer-declaration}.
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\footnote{These declarations were previously allowed in HLSL reference compilers
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but are not supported in this specification.}
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\p Variable declarations with program storage duration
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(\ref{Basic.Storage.Program}) in the cbuffer declaration are called
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\textit{shader constants}. Shader constants are implicitly \texttt{const} and
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cannot be modified in program code.\footnote{A future version of this
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specification will likely disallow variable declarations with storage durations
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other than program storage duration in cbuffer declarations.}

‎specs/language/resources.tex‎

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\Sec{Constant Buffers}{Resources.cnbuf}
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Constant buffers represent resources that contain read-only constant data in a
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well-defined memory layout.
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\Sub{Constant Buffer Declaration Block}{Resources.cnbuf.cb}
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\p A constant buffer can be declared using the \texttt{cbuffer} specifier.
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\begin{grammar}
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\define{cbuffer-declaration-group}\br
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\terminal{cbuffer} name \opt{resource-binding} \terminal{\{}
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\opt{cbuffer-declaration-seq} \terminal {\}}
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\define{cbuffer-declaration-seq}\br
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\textit{cbuffer-declaration}\br
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\textit{cbuffer-declaration-seq cbuffer-declaration}
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\define{cbuffer-declaration}\br
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\textit{variable-declaration}\br
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\textit{empty-declaration}
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\end{grammar}
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\p The name of the \texttt{cbuffer} declaration group cannot be referenced from within the translation unit and is not required to be unique.
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\p Variable declarations in the \texttt{cbuffer} declaration group are called \textit{shader constants}.
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\p Shader constants can be referenced from anywhere in the translation unit after they are declared by directly using the declaration name. This implies that all shader constants declared in a translation unit must have unique names, even though they might be declared in different \texttt{cbuffer} declaration groups.
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\p Variable declarations in the \texttt{cbuffer} declaration group cannot have \texttt{groupshared} or \texttt{static} variable modifiers.
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\p Other declarations in the \texttt{cbuffer} declaration group such as
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\textit{namespace-declaration}, \textit{record-declaration} or
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\textit{function-declaration} are not allowed.
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\p Nesting of \texttt{cbuffer} declaration groups is not allowed.
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\p For example:
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\begin{HLSL}
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cbuffer MyConstants {
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float4 CameraPos;
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};
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float4 getCameraPosition() {
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return CameraPos;
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}
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\end{HLSL}
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\p Constant buffers represent resources that contain read-only constant data in a
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well-defined memory layout. A constant buffer is declared either as a
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cbuffer-declaration (\ref{Decl.cbuffer}) or as a declaration of Constant Buffer
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Class type (\ref{Resources.cnbuf.cbclass}).
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\Sub{Constant Buffer Class}{Resources.cnbuf.cbclass}
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\p Another way of declaring constant buffers is by using the
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\texttt{ConstantBuffer<T>} resource class.
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\p The template parameter \texttt{T} must be a class type (\ref{Classes}).
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\p The template parameter \texttt{T} must be a class type (\ref{Classes}).
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\begin{HLSL}
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template <typename T>

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