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84 lines
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<title>Optimized Code - Debugging with GDB</title>
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<a name="Optimized-Code"></a>
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Next: <a rel="next" accesskey="n" href="Macros.html#Macros">Macros</a>,
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Previous: <a rel="previous" accesskey="p" href="Data.html#Data">Data</a>,
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<h2 class="chapter">11 Debugging Optimized Code</h2>
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<p><a name="index-optimized-code_002c-debugging-834"></a><a name="index-debugging-optimized-code-835"></a>
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Almost all compilers support optimization. With optimization
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disabled, the compiler generates assembly code that corresponds
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directly to your source code, in a simplistic way. As the compiler
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applies more powerful optimizations, the generated assembly code
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diverges from your original source code. With help from debugging
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information generated by the compiler, <span class="sc">gdb</span> can map from
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the running program back to constructs from your original source.
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<p><span class="sc">gdb</span> is more accurate with optimization disabled. If you
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can recompile without optimization, it is easier to follow the
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progress of your program during debugging. But, there are many cases
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where you may need to debug an optimized version.
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<p>When you debug a program compiled with ‘<samp><span class="samp">-g -O</span></samp>’, remember that the
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optimizer has rearranged your code; the debugger shows you what is
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really there. Do not be too surprised when the execution path does not
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exactly match your source file! An extreme example: if you define a
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variable, but never use it, <span class="sc">gdb</span> never sees that
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variable—because the compiler optimizes it out of existence.
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<p>Some things do not work as well with ‘<samp><span class="samp">-g -O</span></samp>’ as with just
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‘<samp><span class="samp">-g</span></samp>’, particularly on machines with instruction scheduling. If in
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doubt, recompile with ‘<samp><span class="samp">-g</span></samp>’ alone, and if this fixes the problem,
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please report it to us as a bug (including a test case!).
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See <a href="Variables.html#Variables">Variables</a>, for more information about debugging optimized code.
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<ul class="menu">
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<li><a accesskey="1" href="Inline-Functions.html#Inline-Functions">Inline Functions</a>: How <span class="sc">gdb</span> presents inlining
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<li><a accesskey="2" href="Tail-Call-Frames.html#Tail-Call-Frames">Tail Call Frames</a>: <span class="sc">gdb</span> analysis of jumps to functions
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</ul>
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</body></html>
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