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100 lines
4.4 KiB
HTML
100 lines
4.4 KiB
HTML
4 years ago
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<html lang="en">
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<title>Expression trees - GNU Compiler Collection (GCC) Internals</title>
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<meta name="description" content="GNU Compiler Collection (GCC) Internals">
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<link title="Top" rel="start" href="index.html#Top">
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<link rel="up" href="GENERIC.html#GENERIC" title="GENERIC">
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<link rel="prev" href="Attributes.html#Attributes" title="Attributes">
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<link rel="next" href="Statements.html#Statements" title="Statements">
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Copyright (C) 1988-2015 Free Software Foundation, Inc.
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Permission is granted to copy, distribute and/or modify this document
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under the terms of the GNU Free Documentation License, Version 1.3 or
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any later version published by the Free Software Foundation; with the
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Invariant Sections being ``Funding Free Software'', the Front-Cover
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(a) The FSF's Front-Cover Text is:
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A GNU Manual
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(b) The FSF's Back-Cover Text is:
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</head>
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<body>
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<div class="node">
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<a name="Expression-trees"></a>
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<p>
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Next: <a rel="next" accesskey="n" href="Statements.html#Statements">Statements</a>,
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Previous: <a rel="previous" accesskey="p" href="Attributes.html#Attributes">Attributes</a>,
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Up: <a rel="up" accesskey="u" href="GENERIC.html#GENERIC">GENERIC</a>
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<hr>
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</div>
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<h3 class="section">10.6 Expressions</h3>
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<p><a name="index-expression-1820"></a><a name="index-TREE_005fTYPE-1821"></a><a name="index-TREE_005fOPERAND-1822"></a>
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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>The following macros can be used with all expression nodes:
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<dl>
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<dt><code>TREE_TYPE</code><a name="index-TREE_005fTYPE-1823"></a><dd>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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</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>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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<pre class="smallexample"> TREE_OPERAND (expr, 0)
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</pre>
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<p class="noindent">As this example indicates, the operands are zero-indexed.
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<ul class="menu">
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<li><a accesskey="1" href="Constant-expressions.html#Constant-expressions">Constants</a>
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<li><a accesskey="2" href="Storage-References.html#Storage-References">Storage References</a>
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<li><a accesskey="3" href="Unary-and-Binary-Expressions.html#Unary-and-Binary-Expressions">Unary and Binary Expressions</a>
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<li><a accesskey="4" href="Vectors.html#Vectors">Vectors</a>
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</ul>
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</body></html>
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