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<title>GNU Compiler Collection (GCC) Internals: Adding new DECL node types</title>
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<a name="Adding-new-DECL-node-types"></a>
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<div class="header">
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<p>
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Previous: <a href="Current-structure-hierarchy.html#Current-structure-hierarchy" accesskey="p" rel="prev">Current structure hierarchy</a>, Up: <a href="Internal-structure.html#Internal-structure" accesskey="u" rel="up">Internal structure</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
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<a name="Adding-new-DECL-node-types-1"></a>
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<h4 class="subsubsection">10.4.2.2 Adding new DECL node types</h4>
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<p>Adding a new <code>DECL</code> tree consists of the following steps
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</p>
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<dl compact="compact">
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<dt>Add a new tree code for the <code>DECL</code> node</dt>
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<dd><p>For language specific <code>DECL</code> nodes, there is a <samp>.def</samp> file
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in each frontend directory where the tree code should be added.
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For <code>DECL</code> nodes that are part of the middle-end, the code should
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be added to <samp>tree.def</samp>.
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</p>
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</dd>
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<dt>Create a new structure type for the <code>DECL</code> node</dt>
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<dd><p>These structures should inherit from one of the existing structures in
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the language hierarchy by using that structure as the first member.
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</p>
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<div class="smallexample">
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<pre class="smallexample">struct tree_foo_decl
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{
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struct tree_decl_with_vis common;
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}
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</pre></div>
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<p>Would create a structure name <code>tree_foo_decl</code> that inherits from
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<code>struct tree_decl_with_vis</code>.
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</p>
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<p>For language specific <code>DECL</code> nodes, this new structure type
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should go in the appropriate <samp>.h</samp> file.
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For <code>DECL</code> nodes that are part of the middle-end, the structure
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type should go in <samp>tree.h</samp>.
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</p>
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</dd>
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<dt>Add a member to the tree structure enumerator for the node</dt>
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<dd><p>For garbage collection and dynamic checking purposes, each <code>DECL</code>
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node structure type is required to have a unique enumerator value
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specified with it.
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For language specific <code>DECL</code> nodes, this new enumerator value
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should go in the appropriate <samp>.def</samp> file.
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For <code>DECL</code> nodes that are part of the middle-end, the enumerator
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values are specified in <samp>treestruct.def</samp>.
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</p>
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</dd>
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<dt>Update <code>union tree_node</code></dt>
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<dd><p>In order to make your new structure type usable, it must be added to
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<code>union tree_node</code>.
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For language specific <code>DECL</code> nodes, a new entry should be added
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to the appropriate <samp>.h</samp> file of the form
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</p><div class="smallexample">
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<pre class="smallexample"> struct tree_foo_decl GTY ((tag ("TS_VAR_DECL"))) foo_decl;
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</pre></div>
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<p>For <code>DECL</code> nodes that are part of the middle-end, the additional
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member goes directly into <code>union tree_node</code> in <samp>tree.h</samp>.
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</p>
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</dd>
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<dt>Update dynamic checking info</dt>
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<dd><p>In order to be able to check whether accessing a named portion of
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<code>union tree_node</code> is legal, and whether a certain <code>DECL</code> node
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contains one of the enumerated <code>DECL</code> node structures in the
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hierarchy, a simple lookup table is used.
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This lookup table needs to be kept up to date with the tree structure
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hierarchy, or else checking and containment macros will fail
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inappropriately.
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</p>
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<p>For language specific <code>DECL</code> nodes, their is an <code>init_ts</code>
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function in an appropriate <samp>.c</samp> file, which initializes the lookup
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table.
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Code setting up the table for new <code>DECL</code> nodes should be added
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there.
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For each <code>DECL</code> tree code and enumerator value representing a
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member of the inheritance hierarchy, the table should contain 1 if
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that tree code inherits (directly or indirectly) from that member.
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Thus, a <code>FOO_DECL</code> node derived from <code>struct decl_with_rtl</code>,
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and enumerator value <code>TS_FOO_DECL</code>, would be set up as follows
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</p><div class="smallexample">
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<pre class="smallexample">tree_contains_struct[FOO_DECL][TS_FOO_DECL] = 1;
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tree_contains_struct[FOO_DECL][TS_DECL_WRTL] = 1;
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tree_contains_struct[FOO_DECL][TS_DECL_COMMON] = 1;
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tree_contains_struct[FOO_DECL][TS_DECL_MINIMAL] = 1;
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</pre></div>
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<p>For <code>DECL</code> nodes that are part of the middle-end, the setup code
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goes into <samp>tree.c</samp>.
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</p>
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</dd>
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<dt>Add macros to access any new fields and flags</dt>
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<dd>
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<p>Each added field or flag should have a macro that is used to access
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it, that performs appropriate checking to ensure only the right type of
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<code>DECL</code> nodes access the field.
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</p>
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<p>These macros generally take the following form
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</p><div class="smallexample">
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<pre class="smallexample">#define FOO_DECL_FIELDNAME(NODE) FOO_DECL_CHECK(NODE)->foo_decl.fieldname
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</pre></div>
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<p>However, if the structure is simply a base class for further
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structures, something like the following should be used
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</p><div class="smallexample">
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<pre class="smallexample">#define BASE_STRUCT_CHECK(T) CONTAINS_STRUCT_CHECK(T, TS_BASE_STRUCT)
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#define BASE_STRUCT_FIELDNAME(NODE) \
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(BASE_STRUCT_CHECK(NODE)->base_struct.fieldname
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</pre></div>
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<p>Reading them from the generated <samp>all-tree.def</samp> file (which in
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turn includes all the <samp>tree.def</samp> files), <samp>gencheck.c</samp> is
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used during GCC’s build to generate the <code>*_CHECK</code> macros for all
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tree codes.
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</p>
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</dd>
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</dl>
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Previous: <a href="Current-structure-hierarchy.html#Current-structure-hierarchy" accesskey="p" rel="prev">Current structure hierarchy</a>, Up: <a href="Internal-structure.html#Internal-structure" accesskey="u" rel="up">Internal structure</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
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