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85 lines
3.7 KiB
HTML
85 lines
3.7 KiB
HTML
4 years ago
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<title>Debug Information - 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="RTL.html#RTL" title="RTL">
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<link rel="prev" href="Assembler.html#Assembler" title="Assembler">
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<link rel="next" href="Insns.html#Insns" title="Insns">
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<link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage">
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<!--
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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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Texts being (a) (see below), and with the Back-Cover Texts being (b)
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(see below). A copy of the license is included in the section entitled
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``GNU Free Documentation License''.
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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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You have freedom to copy and modify this GNU Manual, like GNU
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funds for GNU development.-->
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</head>
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<body>
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<div class="node">
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<a name="Debug-Information"></a>
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<p>
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Next: <a rel="next" accesskey="n" href="Insns.html#Insns">Insns</a>,
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Previous: <a rel="previous" accesskey="p" href="Assembler.html#Assembler">Assembler</a>,
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Up: <a rel="up" accesskey="u" href="RTL.html#RTL">RTL</a>
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<hr>
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</div>
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<h3 class="section">13.18 Variable Location Debug Information in RTL</h3>
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<p><a name="index-Variable-Location-Debug-Information-in-RTL-3064"></a>
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Variable tracking relies on <code>MEM_EXPR</code> and <code>REG_EXPR</code>
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annotations to determine what user variables memory and register
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references refer to.
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<p>Variable tracking at assignments uses these notes only when they refer
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to variables that live at fixed locations (e.g., addressable
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variables, global non-automatic variables). For variables whose
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location may vary, it relies on the following types of notes.
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<a name="index-var_005flocation-3065"></a>
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<dl><dt><code>(var_location:</code><var>mode</var> <var>var</var> <var>exp</var> <var>stat</var><code>)</code><dd>Binds variable <code>var</code>, a tree, to value <var>exp</var>, an RTL
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expression. It appears only in <code>NOTE_INSN_VAR_LOCATION</code> and
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<code>DEBUG_INSN</code>s, with slightly different meanings. <var>mode</var>, if
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present, represents the mode of <var>exp</var>, which is useful if it is a
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modeless expression. <var>stat</var> is only meaningful in notes,
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indicating whether the variable is known to be initialized or
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uninitialized.
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<p><a name="index-debug_005fexpr-3066"></a><br><dt><code>(debug_expr:</code><var>mode</var> <var>decl</var><code>)</code><dd>Stands for the value bound to the <code>DEBUG_EXPR_DECL</code> <var>decl</var>,
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that points back to it, within value expressions in
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<code>VAR_LOCATION</code> nodes.
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</dl>
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</body></html>
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