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| author | alk3pInjection <webmaster@raspii.tech> | 2024-02-04 16:16:35 +0800 |
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| committer | alk3pInjection <webmaster@raspii.tech> | 2024-02-04 16:16:35 +0800 |
| commit | abdaadbcae30fe0c9a66c7516798279fdfd97750 (patch) | |
| tree | 00a54a6e25601e43876d03c1a4a12a749d4a914c /share/doc/gcc/Gcov-and-Optimization.html | |
https://developer.arm.com/downloads/-/arm-gnu-toolchain-downloads
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diff --git a/share/doc/gcc/Gcov-and-Optimization.html b/share/doc/gcc/Gcov-and-Optimization.html new file mode 100644 index 0000000..5604544 --- /dev/null +++ b/share/doc/gcc/Gcov-and-Optimization.html @@ -0,0 +1,169 @@ +<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> +<html> +<!-- This file documents the use of the GNU compilers. + +Copyright (C) 1988-2023 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. --> +<!-- Created by GNU Texinfo 5.1, http://www.gnu.org/software/texinfo/ --> +<head> +<title>Using the GNU Compiler Collection (GCC): Gcov and Optimization</title> + +<meta name="description" content="Using the GNU Compiler Collection (GCC): Gcov and Optimization"> +<meta name="keywords" content="Using the GNU Compiler Collection (GCC): Gcov and Optimization"> +<meta name="resource-type" content="document"> +<meta name="distribution" content="global"> +<meta name="Generator" content="makeinfo"> +<meta http-equiv="Content-Type" content="text/html; charset=utf-8"> +<link href="index.html#Top" rel="start" title="Top"> +<link href="Indices.html#Indices" rel="index" title="Indices"> +<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents"> +<link href="Gcov.html#Gcov" rel="up" title="Gcov"> +<link href="Gcov-Data-Files.html#Gcov-Data-Files" rel="next" title="Gcov Data Files"> +<link href="Invoking-Gcov.html#Invoking-Gcov" rel="previous" title="Invoking Gcov"> +<style type="text/css"> +<!-- +a.summary-letter {text-decoration: none} +blockquote.smallquotation {font-size: smaller} +div.display {margin-left: 3.2em} +div.example {margin-left: 3.2em} +div.indentedblock {margin-left: 3.2em} +div.lisp {margin-left: 3.2em} +div.smalldisplay {margin-left: 3.2em} +div.smallexample {margin-left: 3.2em} +div.smallindentedblock {margin-left: 3.2em; font-size: smaller} +div.smalllisp {margin-left: 3.2em} +kbd {font-style:oblique} +pre.display {font-family: inherit} +pre.format {font-family: inherit} +pre.menu-comment {font-family: serif} +pre.menu-preformatted {font-family: serif} +pre.smalldisplay {font-family: inherit; font-size: smaller} +pre.smallexample {font-size: smaller} +pre.smallformat {font-family: inherit; font-size: smaller} +pre.smalllisp {font-size: smaller} +span.nocodebreak {white-space:nowrap} +span.nolinebreak {white-space:nowrap} +span.roman {font-family:serif; font-weight:normal} +span.sansserif {font-family:sans-serif; font-weight:normal} +ul.no-bullet {list-style: none} +--> +</style> + + +</head> + +<body lang="en_US" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000"> +<a name="Gcov-and-Optimization"></a> +<div class="header"> +<p> +Next: <a href="Gcov-Data-Files.html#Gcov-Data-Files" accesskey="n" rel="next">Gcov Data Files</a>, Previous: <a href="Invoking-Gcov.html#Invoking-Gcov" accesskey="p" rel="previous">Invoking Gcov</a>, Up: <a href="Gcov.html#Gcov" accesskey="u" rel="up">Gcov</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Indices.html#Indices" title="Index" rel="index">Index</a>]</p> +</div> +<hr> +<a name="Using-gcov-with-GCC-Optimization"></a> +<h3 class="section">10.3 Using <code>gcov</code> with GCC Optimization</h3> + +<p>If you plan to use <code>gcov</code> to help optimize your code, you must +first compile your program with a special GCC option +‘<samp>--coverage</samp>’. Aside from that, you can use any +other GCC options; but if you want to prove that every single line +in your program was executed, you should not compile with optimization +at the same time. On some machines the optimizer can eliminate some +simple code lines by combining them with other lines. For example, code +like this: +</p> +<div class="smallexample"> +<pre class="smallexample">if (a != b) + c = 1; +else + c = 0; +</pre></div> + +<p>can be compiled into one instruction on some machines. In this case, +there is no way for <code>gcov</code> to calculate separate execution counts +for each line because there isn’t separate code for each line. Hence +the <code>gcov</code> output looks like this if you compiled the program with +optimization: +</p> +<div class="smallexample"> +<pre class="smallexample"> 100: 12:if (a != b) + 100: 13: c = 1; + 100: 14:else + 100: 15: c = 0; +</pre></div> + +<p>The output shows that this block of code, combined by optimization, +executed 100 times. In one sense this result is correct, because there +was only one instruction representing all four of these lines. However, +the output does not indicate how many times the result was 0 and how +many times the result was 1. +</p> +<p>Inlineable functions can create unexpected line counts. Line counts are +shown for the source code of the inlineable function, but what is shown +depends on where the function is inlined, or if it is not inlined at all. +</p> +<p>If the function is not inlined, the compiler must emit an out of line +copy of the function, in any object file that needs it. If +<samp>fileA.o</samp> and <samp>fileB.o</samp> both contain out of line bodies of a +particular inlineable function, they will also both contain coverage +counts for that function. When <samp>fileA.o</samp> and <samp>fileB.o</samp> are +linked together, the linker will, on many systems, select one of those +out of line bodies for all calls to that function, and remove or ignore +the other. Unfortunately, it will not remove the coverage counters for +the unused function body. Hence when instrumented, all but one use of +that function will show zero counts. +</p> +<p>If the function is inlined in several places, the block structure in +each location might not be the same. For instance, a condition might +now be calculable at compile time in some instances. Because the +coverage of all the uses of the inline function will be shown for the +same source lines, the line counts themselves might seem inconsistent. +</p> +<p>Long-running applications can use the <code>__gcov_reset</code> and <code>__gcov_dump</code> +facilities to restrict profile collection to the program region of +interest. Calling <code>__gcov_reset(void)</code> will clear all run-time profile +counters to zero, and calling <code>__gcov_dump(void)</code> will cause the profile +information collected at that point to be dumped to <samp>.gcda</samp> output files. +Instrumented applications use a static destructor with priority 99 +to invoke the <code>__gcov_dump</code> function. Thus <code>__gcov_dump</code> +is executed after all user defined static destructors, +as well as handlers registered with <code>atexit</code>. +</p> +<p>If an executable loads a dynamic shared object via dlopen functionality, +<samp>-Wl,--dynamic-list-data</samp> is needed to dump all profile data. +</p> +<p>Profiling run-time library reports various errors related to profile +manipulation and profile saving. Errors are printed into standard error output +or ‘<samp>GCOV_ERROR_FILE</samp>’ file, if environment variable is used. +In order to terminate immediately after an errors occurs +set ‘<samp>GCOV_EXIT_AT_ERROR</samp>’ environment variable. +That can help users to find profile clashing which leads +to a misleading profile. +</p> + +<hr> +<div class="header"> +<p> +Next: <a href="Gcov-Data-Files.html#Gcov-Data-Files" accesskey="n" rel="next">Gcov Data Files</a>, Previous: <a href="Invoking-Gcov.html#Invoking-Gcov" accesskey="p" rel="previous">Invoking Gcov</a>, Up: <a href="Gcov.html#Gcov" accesskey="u" rel="up">Gcov</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Indices.html#Indices" title="Index" rel="index">Index</a>]</p> +</div> + + + +</body> +</html> |