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101 lines
4.3 KiB
HTML
101 lines
4.3 KiB
HTML
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<head>
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<title>Compound Lvalues (GNU Compiler Collection (GCC) Internals)</title>
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<meta name="description" content="Compound Lvalues (GNU Compiler Collection (GCC) Internals)">
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<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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<link href="Operands.html#Operands" rel="up" title="Operands">
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<link href="Conditional-Expressions.html#Conditional-Expressions" rel="next" title="Conditional Expressions">
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<a name="Compound-Lvalues"></a>
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<div class="header">
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<p>
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Next: <a href="Conditional-Expressions.html#Conditional-Expressions" accesskey="n" rel="next">Conditional Expressions</a>, Previous: <a href="Compound-Expressions.html#Compound-Expressions" accesskey="p" rel="prev">Compound Expressions</a>, Up: <a href="Operands.html#Operands" accesskey="u" rel="up">Operands</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="Compound-Lvalues-1"></a>
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<h4 class="subsection">12.6.2 Compound Lvalues</h4>
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<a name="index-Compound-Lvalues"></a>
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<p>Currently compound lvalues involving array and structure field references
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are not broken down; an expression like <code>a.b[2] = 42</code> is not reduced
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any further (though complex array subscripts are). This restriction is a
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workaround for limitations in later optimizers; if we were to convert this
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to
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</p>
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<div class="smallexample">
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<pre class="smallexample">T1 = &a.b;
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T1[2] = 42;
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</pre></div>
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<p>alias analysis would not remember that the reference to <code>T1[2]</code> came
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by way of <code>a.b</code>, so it would think that the assignment could alias
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another member of <code>a</code>; this broke <code>struct-alias-1.c</code>. Future
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optimizer improvements may make this limitation unnecessary.
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</p>
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</html>
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