<html lang="en">
<head>
<title>Debug Information - GNU Compiler Collection (GCC) Internals</title>
<meta http-equiv="Content-Type" content="text/html">
<meta name="description" content="GNU Compiler Collection (GCC) Internals">
<meta name="generator" content="makeinfo 4.13">
<link title="Top" rel="start" href="index.html#Top">
<link rel="up" href="RTL.html#RTL" title="RTL">
<link rel="prev" href="Assembler.html#Assembler" title="Assembler">
<link rel="next" href="Insns.html#Insns" title="Insns">
<link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage">
<!--
Copyright (C) 1988-2015 Free Software Foundation, Inc.
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.3 or
any later version published by the Free Software Foundation; with the
Invariant Sections being ``Funding Free Software'', the Front-Cover
Texts being (a) (see below), and with the Back-Cover Texts being (b)
(see below). A copy of the license is included in the section entitled
``GNU Free Documentation License''.
(a) The FSF's Front-Cover Text is:
A GNU Manual
(b) The FSF's Back-Cover Text is:
You have freedom to copy and modify this GNU Manual, like GNU
software. Copies published by the Free Software Foundation raise
funds for GNU development.-->
<meta http-equiv="Content-Style-Type" content="text/css">
<style type="text/css"><!--
pre.display { font-family:inherit }
pre.format { font-family:inherit }
pre.smalldisplay { font-family:inherit; font-size:smaller }
pre.smallformat { font-family:inherit; font-size:smaller }
pre.smallexample { font-size:smaller }
pre.smalllisp { font-size:smaller }
span.sc { font-variant:small-caps }
span.roman { font-family:serif; font-weight:normal; }
span.sansserif { font-family:sans-serif; font-weight:normal; }
--></style>
</head>
<body>
<div class="node">
<a name="Debug-Information"></a>
<p>
Next: <a rel="next" accesskey="n" href="Insns.html#Insns">Insns</a>,
Previous: <a rel="previous" accesskey="p" href="Assembler.html#Assembler">Assembler</a>,
Up: <a rel="up" accesskey="u" href="RTL.html#RTL">RTL</a>
<hr>
</div>
<h3 class="section">13.18 Variable Location Debug Information in RTL</h3>
<p><a name="index-Variable-Location-Debug-Information-in-RTL-3064"></a>
Variable tracking relies on <code>MEM_EXPR</code> and <code>REG_EXPR</code>
annotations to determine what user variables memory and register
references refer to.
<p>Variable tracking at assignments uses these notes only when they refer
to variables that live at fixed locations (e.g., addressable
variables, global non-automatic variables). For variables whose
location may vary, it relies on the following types of notes.
<a name="index-var_005flocation-3065"></a>
<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
expression. It appears only in <code>NOTE_INSN_VAR_LOCATION</code> and
<code>DEBUG_INSN</code>s, with slightly different meanings. <var>mode</var>, if
present, represents the mode of <var>exp</var>, which is useful if it is a
modeless expression. <var>stat</var> is only meaningful in notes,
indicating whether the variable is known to be initialized or
uninitialized.
<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>,
that points back to it, within value expressions in
<code>VAR_LOCATION</code> nodes.
</dl>
</body></html>