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 <a name="Bug-Criteria"></a>
 <div class="header">
 <p>
 Next: <a href="Bug-Reporting.html#Bug-Reporting" accesskey="n" rel="next">Bug Reporting</a>, Up: <a href="Bugs.html#Bugs" accesskey="u" rel="up">Bugs</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
 </div>
 <hr>
 <a name="Have-You-Found-a-Bug_003f"></a>
 <h3 class="section">12.1 Have You Found a Bug?</h3>
 <a name="index-bug-criteria"></a>

 <p>If you are not sure whether you have found a bug, here are some guidelines:
 </p>
 <ul>
 <li> <a name="index-fatal-signal"></a>
 <a name="index-core-dump"></a>
 If the compiler gets a fatal signal, for any input whatever, that is a
 compiler bug.  Reliable compilers never crash.

 </li><li> <a name="index-invalid-assembly-code"></a>
 <a name="index-assembly-code_002c-invalid"></a>
 If the compiler produces invalid assembly code, for any input whatever
 (except an <code>asm</code> statement), that is a compiler bug, unless the
 compiler reports errors (not just warnings) which would ordinarily
 prevent the assembler from being run.

 </li><li> <a name="index-undefined-behavior"></a>
 <a name="index-undefined-function-value"></a>
 <a name="index-increment-operators"></a>
 If the compiler produces valid assembly code that does not correctly
 execute the input source code, that is a compiler bug.

 <p>However, you must double-check to make sure, because you may have a
 program whose behavior is undefined, which happened by chance to give
 the desired results with another C or C++ compiler.
 </p>
 <p>For example, in many nonoptimizing compilers, you can write &lsquo;<samp>x;</samp>&rsquo;
 at the end of a function instead of &lsquo;<samp>return x;</samp>&rsquo;, with the same
 results.  But the value of the function is undefined if <code>return</code>
 is omitted; it is not a bug when GCC produces different results.
 </p>
 <p>Problems often result from expressions with two increment operators,
 as in <code>f (*p++, *p++)</code>.  Your previous compiler might have
 interpreted that expression the way you intended; GCC might
 interpret it another way.  Neither compiler is wrong.  The bug is
 in your code.
 </p>
 <p>After you have localized the error to a single source line, it should
 be easy to check for these things.  If your program is correct and
 well defined, you have found a compiler bug.
 </p>
 </li><li> If the compiler produces an error message for valid input, that is a
 compiler bug.

 </li><li> <a name="index-invalid-input"></a>
 If the compiler does not produce an error message for invalid input,
 that is a compiler bug.  However, you should note that your idea of
 &ldquo;invalid input&rdquo; might be someone else&rsquo;s idea of &ldquo;an extension&rdquo; or
 &ldquo;support for traditional practice&rdquo;.

 </li><li> If you are an experienced user of one of the languages GCC supports, your
 suggestions for improvement of GCC are welcome in any case.
 </li></ul>

 <hr>
 <div class="header">
 <p>
 Next: <a href="Bug-Reporting.html#Bug-Reporting" accesskey="n" rel="next">Bug Reporting</a>, Up: <a href="Bugs.html#Bugs" accesskey="u" rel="up">Bugs</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
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	Invariant Sections being "Funding Free Software", the Front-Cover
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	<a name="Bug-Criteria"></a>
	<div class="header">
	<p>
	Next: <a href="Bug-Reporting.html#Bug-Reporting" accesskey="n" rel="next">Bug Reporting</a>, Up: <a href="Bugs.html#Bugs" accesskey="u" rel="up">Bugs</a>   [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
	</div>
	<hr>
	<a name="Have-You-Found-a-Bug_003f"></a>
	<h3 class="section">12.1 Have You Found a Bug?</h3>
	<a name="index-bug-criteria"></a>

	<p>If you are not sure whether you have found a bug, here are some guidelines:
	</p>
	<ul>
	<li> <a name="index-fatal-signal"></a>
	<a name="index-core-dump"></a>
	If the compiler gets a fatal signal, for any input whatever, that is a
	compiler bug. Reliable compilers never crash.

	</li><li> <a name="index-invalid-assembly-code"></a>
	<a name="index-assembly-code_002c-invalid"></a>
	If the compiler produces invalid assembly code, for any input whatever
	(except an <code>asm</code> statement), that is a compiler bug, unless the
	compiler reports errors (not just warnings) which would ordinarily
	prevent the assembler from being run.

	</li><li> <a name="index-undefined-behavior"></a>
	<a name="index-undefined-function-value"></a>
	<a name="index-increment-operators"></a>
	If the compiler produces valid assembly code that does not correctly
	execute the input source code, that is a compiler bug.

	<p>However, you must double-check to make sure, because you may have a
	program whose behavior is undefined, which happened by chance to give
	the desired results with another C or C++ compiler.
	</p>
	<p>For example, in many nonoptimizing compilers, you can write ‘<samp>x;</samp>’
	at the end of a function instead of ‘<samp>return x;</samp>’, with the same
	results. But the value of the function is undefined if <code>return</code>
	is omitted; it is not a bug when GCC produces different results.
	</p>
	<p>Problems often result from expressions with two increment operators,
	as in <code>f (p++, p++)</code>. Your previous compiler might have
	interpreted that expression the way you intended; GCC might
	interpret it another way. Neither compiler is wrong. The bug is
	in your code.
	</p>
	<p>After you have localized the error to a single source line, it should
	be easy to check for these things. If your program is correct and
	well defined, you have found a compiler bug.
	</p>
	</li><li> If the compiler produces an error message for valid input, that is a
	compiler bug.

	</li><li> <a name="index-invalid-input"></a>
	If the compiler does not produce an error message for invalid input,
	that is a compiler bug. However, you should note that your idea of
	“invalid input” might be someone else’s idea of “an extension” or
	“support for traditional practice”.

	</li><li> If you are an experienced user of one of the languages GCC supports, your
	suggestions for improvement of GCC are welcome in any case.
	</li></ul>

	<hr>
	<div class="header">
	<p>
	Next: <a href="Bug-Reporting.html#Bug-Reporting" accesskey="n" rel="next">Bug Reporting</a>, Up: <a href="Bugs.html#Bugs" accesskey="u" rel="up">Bugs</a>   [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
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