1<html lang="en"> 2<head> 3<title>Bug Criteria - Using the GNU Compiler Collection (GCC)</title> 4<meta http-equiv="Content-Type" content="text/html"> 5<meta name="description" content="Using the GNU Compiler Collection (GCC)"> 6<meta name="generator" content="makeinfo 4.13"> 7<link title="Top" rel="start" href="index.html#Top"> 8<link rel="up" href="Bugs.html#Bugs" title="Bugs"> 9<link rel="next" href="Bug-Reporting.html#Bug-Reporting" title="Bug Reporting"> 10<link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage"> 11<!-- 12Copyright (C) 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 131998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 142010 Free Software Foundation, Inc. 15 16Permission is granted to copy, distribute and/or modify this document 17under the terms of the GNU Free Documentation License, Version 1.3 or 18any later version published by the Free Software Foundation; with the 19Invariant Sections being ``Funding Free Software'', the Front-Cover 20Texts being (a) (see below), and with the Back-Cover Texts being (b) 21(see below). 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Reliable compilers never crash. 66 67 <p><a name="index-invalid-assembly-code-3356"></a><a name="index-assembly-code_002c-invalid-3357"></a><li>If the compiler produces invalid assembly code, for any input whatever 68(except an <code>asm</code> statement), that is a compiler bug, unless the 69compiler reports errors (not just warnings) which would ordinarily 70prevent the assembler from being run. 71 72 <p><a name="index-undefined-behavior-3358"></a><a name="index-undefined-function-value-3359"></a><a name="index-increment-operators-3360"></a><li>If the compiler produces valid assembly code that does not correctly 73execute the input source code, that is a compiler bug. 74 75 <p>However, you must double-check to make sure, because you may have a 76program whose behavior is undefined, which happened by chance to give 77the desired results with another C or C++ compiler. 78 79 <p>For example, in many nonoptimizing compilers, you can write ‘<samp><span class="samp">x;</span></samp>’ 80at the end of a function instead of ‘<samp><span class="samp">return x;</span></samp>’, with the same 81results. But the value of the function is undefined if <code>return</code> 82is omitted; it is not a bug when GCC produces different results. 83 84 <p>Problems often result from expressions with two increment operators, 85as in <code>f (*p++, *p++)</code>. Your previous compiler might have 86interpreted that expression the way you intended; GCC might 87interpret it another way. Neither compiler is wrong. The bug is 88in your code. 89 90 <p>After you have localized the error to a single source line, it should 91be easy to check for these things. If your program is correct and 92well defined, you have found a compiler bug. 93 94 <li>If the compiler produces an error message for valid input, that is a 95compiler bug. 96 97 <p><a name="index-invalid-input-3361"></a><li>If the compiler does not produce an error message for invalid input, 98that is a compiler bug. However, you should note that your idea of 99“invalid input” might be someone else's idea of “an extension” or 100“support for traditional practice”. 101 102 <li>If you are an experienced user of one of the languages GCC supports, your 103suggestions for improvement of GCC are welcome in any case. 104</ul> 105 106 </body></html> 107 108