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| Next: <a href="Macros.html#Macros" accesskey="n" rel="next">Macros</a>, Previous: <a href="Data.html#Data" accesskey="p" rel="prev">Data</a>, Up: <a href="index.html#Top" accesskey="u" rel="up">Top</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p> |
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| <a name="Debugging-Optimized-Code"></a> |
| <h2 class="chapter">11 Debugging Optimized Code</h2> |
| <a name="index-optimized-code_002c-debugging"></a> |
| <a name="index-debugging-optimized-code"></a> |
| |
| <p>Almost all compilers support optimization. With optimization |
| disabled, the compiler generates assembly code that corresponds |
| directly to your source code, in a simplistic way. As the compiler |
| applies more powerful optimizations, the generated assembly code |
| diverges from your original source code. With help from debugging |
| information generated by the compiler, <small>GDB</small> can map from |
| the running program back to constructs from your original source. |
| </p> |
| <p><small>GDB</small> is more accurate with optimization disabled. If you |
| can recompile without optimization, it is easier to follow the |
| progress of your program during debugging. But, there are many cases |
| where you may need to debug an optimized version. |
| </p> |
| <p>When you debug a program compiled with ‘<samp>-g -O</samp>’, remember that the |
| optimizer has rearranged your code; the debugger shows you what is |
| really there. Do not be too surprised when the execution path does not |
| exactly match your source file! An extreme example: if you define a |
| variable, but never use it, <small>GDB</small> never sees that |
| variable—because the compiler optimizes it out of existence. |
| </p> |
| <p>Some things do not work as well with ‘<samp>-g -O</samp>’ as with just |
| ‘<samp>-g</samp>’, particularly on machines with instruction scheduling. If in |
| doubt, recompile with ‘<samp>-g</samp>’ alone, and if this fixes the problem, |
| please report it to us as a bug (including a test case!). |
| See <a href="Variables.html#Variables">Variables</a>, for more information about debugging optimized code. |
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| <table class="menu" border="0" cellspacing="0"> |
| <tr><td align="left" valign="top">• <a href="Inline-Functions.html#Inline-Functions" accesskey="1">Inline Functions</a>:</td><td> </td><td align="left" valign="top">How <small>GDB</small> presents inlining |
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| <tr><td align="left" valign="top">• <a href="Tail-Call-Frames.html#Tail-Call-Frames" accesskey="2">Tail Call Frames</a>:</td><td> </td><td align="left" valign="top"><small>GDB</small> analysis of jumps to functions |
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