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143 lines
6.5 KiB
HTML
143 lines
6.5 KiB
HTML
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<head>
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<title>Expression trees (GNU Compiler Collection (GCC) Internals)</title>
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<meta name="description" content="Expression trees (GNU Compiler Collection (GCC) Internals)">
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<link href="index.html#Top" rel="start" title="Top">
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<link href="Option-Index.html#Option-Index" rel="index" title="Option Index">
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<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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<link href="GENERIC.html#GENERIC" rel="up" title="GENERIC">
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<link href="Constant-expressions.html#Constant-expressions" rel="next" title="Constant expressions">
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<link href="Attributes.html#Attributes" rel="prev" title="Attributes">
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<a name="Expression-trees"></a>
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<div class="header">
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<p>
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Next: <a href="Statements.html#Statements" accesskey="n" rel="next">Statements</a>, Previous: <a href="Attributes.html#Attributes" accesskey="p" rel="prev">Attributes</a>, Up: <a href="GENERIC.html#GENERIC" accesskey="u" rel="up">GENERIC</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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</div>
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<hr>
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<a name="Expressions-1"></a>
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<h3 class="section">11.6 Expressions</h3>
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<a name="index-expression"></a>
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<a name="index-TREE_005fTYPE-3"></a>
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<a name="index-TREE_005fOPERAND"></a>
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<p>The internal representation for expressions is for the most part quite
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straightforward. However, there are a few facts that one must bear in
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mind. In particular, the expression “tree” is actually a directed
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acyclic graph. (For example there may be many references to the integer
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constant zero throughout the source program; many of these will be
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represented by the same expression node.) You should not rely on
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certain kinds of node being shared, nor should you rely on certain kinds of
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nodes being unshared.
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</p>
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<p>The following macros can be used with all expression nodes:
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</p>
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<dl compact="compact">
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<dt><code>TREE_TYPE</code>
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<a name="index-TREE_005fTYPE-4"></a>
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</dt>
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<dd><p>Returns the type of the expression. This value may not be precisely the
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same type that would be given the expression in the original program.
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</p></dd>
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</dl>
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<p>In what follows, some nodes that one might expect to always have type
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<code>bool</code> are documented to have either integral or boolean type. At
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some point in the future, the C front end may also make use of this same
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intermediate representation, and at this point these nodes will
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certainly have integral type. The previous sentence is not meant to
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imply that the C++ front end does not or will not give these nodes
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integral type.
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</p>
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<p>Below, we list the various kinds of expression nodes. Except where
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noted otherwise, the operands to an expression are accessed using the
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<code>TREE_OPERAND</code> macro. For example, to access the first operand to
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a binary plus expression <code>expr</code>, use:
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</p>
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<div class="smallexample">
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<pre class="smallexample">TREE_OPERAND (expr, 0)
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</pre></div>
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<p>As this example indicates, the operands are zero-indexed.
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</p>
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<table class="menu" border="0" cellspacing="0">
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<tr><td align="left" valign="top">• <a href="Constant-expressions.html#Constant-expressions" accesskey="1">Constants</a>:</td><td> </td><td align="left" valign="top">
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</td></tr>
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<tr><td align="left" valign="top">• <a href="Storage-References.html#Storage-References" accesskey="2">Storage References</a>:</td><td> </td><td align="left" valign="top">
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</td></tr>
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<tr><td align="left" valign="top">• <a href="Unary-and-Binary-Expressions.html#Unary-and-Binary-Expressions" accesskey="3">Unary and Binary Expressions</a>:</td><td> </td><td align="left" valign="top">
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</td></tr>
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<tr><td align="left" valign="top">• <a href="Vectors.html#Vectors" accesskey="4">Vectors</a>:</td><td> </td><td align="left" valign="top">
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</td></tr>
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</table>
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<hr>
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<div class="header">
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<p>
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Next: <a href="Statements.html#Statements" accesskey="n" rel="next">Statements</a>, Previous: <a href="Attributes.html#Attributes" accesskey="p" rel="prev">Attributes</a>, Up: <a href="GENERIC.html#GENERIC" accesskey="u" rel="up">GENERIC</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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