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| <a name="Caller_002dSaves-Register-Allocation"></a> |
| <h4 class="subsection">17.10.10 Caller-Saves Register Allocation</h4> |
| |
| <p>If you enable it, GCC can save registers around function calls. This |
| makes it possible to use call-clobbered registers to hold variables that |
| must live across calls. |
| </p> |
| <dl> |
| <dt><a name="index-CALLER_005fSAVE_005fPROFITABLE"></a>Macro: <strong>CALLER_SAVE_PROFITABLE</strong> <em>(<var>refs</var>, <var>calls</var>)</em></dt> |
| <dd><p>A C expression to determine whether it is worthwhile to consider placing |
| a pseudo-register in a call-clobbered hard register and saving and |
| restoring it around each function call. The expression should be 1 when |
| this is worth doing, and 0 otherwise. |
| </p> |
| <p>If you don’t define this macro, a default is used which is good on most |
| machines: <code>4 * <var>calls</var> < <var>refs</var></code>. |
| </p></dd></dl> |
| |
| <dl> |
| <dt><a name="index-HARD_005fREGNO_005fCALLER_005fSAVE_005fMODE"></a>Macro: <strong>HARD_REGNO_CALLER_SAVE_MODE</strong> <em>(<var>regno</var>, <var>nregs</var>)</em></dt> |
| <dd><p>A C expression specifying which mode is required for saving <var>nregs</var> |
| of a pseudo-register in call-clobbered hard register <var>regno</var>. If |
| <var>regno</var> is unsuitable for caller save, <code>VOIDmode</code> should be |
| returned. For most machines this macro need not be defined since GCC |
| will select the smallest suitable mode. |
| </p></dd></dl> |
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