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