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<h3 class="section">4.8 Hints</h3>

     <ul>
<li><cite>The extent to which suggestions made by using the </cite><code>register</code><cite>
storage-class specifier are effective (C90 6.5.1, C99 6.7.1).</cite>

     <p>The <code>register</code> specifier affects code generation only in these ways:

          <ul>
<li>When used as part of the register variable extension, see
<a href="Explicit-Reg-Vars.html#Explicit-Reg-Vars">Explicit Reg Vars</a>.

          <li>When <samp><span class="option">-O0</span></samp> is in use, the compiler allocates distinct stack
memory for all variables that do not have the <code>register</code>
storage-class specifier; if <code>register</code> is specified, the variable
may have a shorter lifespan than the code would indicate and may never
be placed in memory.

          <li>On some rare x86 targets, <code>setjmp</code> doesn't save the registers in
all circumstances.  In those cases, GCC doesn't allocate any variables
in registers unless they are marked <code>register</code>.

     </ul>

     <li><cite>The extent to which suggestions made by using the inline function
specifier are effective (C99 6.7.4).</cite>

     <p>GCC will not inline any functions if the <samp><span class="option">-fno-inline</span></samp> option is
used or if <samp><span class="option">-O0</span></samp> is used.  Otherwise, GCC may still be unable to
inline a function for many reasons; the <samp><span class="option">-Winline</span></samp> option may be
used to determine if a function has not been inlined and why not.

</ul>

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