<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>