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| <a name="GENERIC-1"></a> |
| <h2 class="chapter">10 GENERIC</h2> |
| <a name="index-GENERIC-1"></a> |
| |
| <p>The purpose of GENERIC is simply to provide a |
| language-independent way of representing an entire function in |
| trees. To this end, it was necessary to add a few new tree codes |
| to the back end, but almost everything was already there. If you |
| can express it with the codes in <code>gcc/tree.def</code>, it’s |
| GENERIC. |
| </p> |
| <p>Early on, there was a great deal of debate about how to think |
| about statements in a tree IL. In GENERIC, a statement is |
| defined as any expression whose value, if any, is ignored. A |
| statement will always have <code>TREE_SIDE_EFFECTS</code> set (or it |
| will be discarded), but a non-statement expression may also have |
| side effects. A <code>CALL_EXPR</code>, for instance. |
| </p> |
| <p>It would be possible for some local optimizations to work on the |
| GENERIC form of a function; indeed, the adapted tree inliner |
| works fine on GENERIC, but the current compiler performs inlining |
| after lowering to GIMPLE (a restricted form described in the next |
| section). Indeed, currently the frontends perform this lowering |
| before handing off to <code>tree_rest_of_compilation</code>, but this |
| seems inelegant. |
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| <tr><td align="left" valign="top">• <a href="Deficiencies.html#Deficiencies" accesskey="1">Deficiencies</a>:</td><td> </td><td align="left" valign="top">Topics net yet covered in this document. |
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| <tr><td align="left" valign="top">• <a href="Tree-overview.html#Tree-overview" accesskey="2">Tree overview</a>:</td><td> </td><td align="left" valign="top">All about <code>tree</code>s. |
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| <tr><td align="left" valign="top">• <a href="Types.html#Types" accesskey="3">Types</a>:</td><td> </td><td align="left" valign="top">Fundamental and aggregate types. |
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| <tr><td align="left" valign="top">• <a href="Declarations.html#Declarations" accesskey="4">Declarations</a>:</td><td> </td><td align="left" valign="top">Type declarations and variables. |
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| <tr><td align="left" valign="top">• <a href="Statements.html#Statements" accesskey="7">Statements</a>:</td><td> </td><td align="left" valign="top">Control flow and related trees. |
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| <tr><td align="left" valign="top">• <a href="Functions.html#Functions" accesskey="8">Functions</a>:</td><td> </td><td align="left" valign="top">Function bodies, linkage, and other aspects. |
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| <tr><td align="left" valign="top">• <a href="Language_002ddependent-trees.html#Language_002ddependent-trees" accesskey="9">Language-dependent trees</a>:</td><td> </td><td align="left" valign="top">Topics and trees specific to language front ends. |
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| <tr><td align="left" valign="top">• <a href="C-and-C_002b_002b-Trees.html#C-and-C_002b_002b-Trees">C and C++ Trees</a>:</td><td> </td><td align="left" valign="top">Trees specific to C and C++. |
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| <tr><td align="left" valign="top">• <a href="Java-Trees.html#Java-Trees">Java Trees</a>:</td><td> </td><td align="left" valign="top">Trees specific to Java. |
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