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| <a name="Order-of-Allocation-of-Registers"></a> |
| <h4 class="subsection">17.7.2 Order of Allocation of Registers</h4> |
| <a name="index-order-of-register-allocation"></a> |
| <a name="index-register-allocation-order"></a> |
| |
| <p>Registers are allocated in order. |
| </p> |
| <dl> |
| <dt><a name="index-REG_005fALLOC_005fORDER"></a>Macro: <strong>REG_ALLOC_ORDER</strong></dt> |
| <dd><p>If defined, an initializer for a vector of integers, containing the |
| numbers of hard registers in the order in which GCC should prefer |
| to use them (from most preferred to least). |
| </p> |
| <p>If this macro is not defined, registers are used lowest numbered first |
| (all else being equal). |
| </p> |
| <p>One use of this macro is on machines where the highest numbered |
| registers must always be saved and the save-multiple-registers |
| instruction supports only sequences of consecutive registers. On such |
| machines, define <code>REG_ALLOC_ORDER</code> to be an initializer that lists |
| the highest numbered allocable register first. |
| </p></dd></dl> |
| |
| <dl> |
| <dt><a name="index-ADJUST_005fREG_005fALLOC_005fORDER"></a>Macro: <strong>ADJUST_REG_ALLOC_ORDER</strong></dt> |
| <dd><p>A C statement (sans semicolon) to choose the order in which to allocate |
| hard registers for pseudo-registers local to a basic block. |
| </p> |
| <p>Store the desired register order in the array <code>reg_alloc_order</code>. |
| Element 0 should be the register to allocate first; element 1, the next |
| register; and so on. |
| </p> |
| <p>The macro body should not assume anything about the contents of |
| <code>reg_alloc_order</code> before execution of the macro. |
| </p> |
| <p>On most machines, it is not necessary to define this macro. |
| </p></dd></dl> |
| |
| <dl> |
| <dt><a name="index-HONOR_005fREG_005fALLOC_005fORDER"></a>Macro: <strong>HONOR_REG_ALLOC_ORDER</strong></dt> |
| <dd><p>Normally, IRA tries to estimate the costs for saving a register in the |
| prologue and restoring it in the epilogue. This discourages it from |
| using call-saved registers. If a machine wants to ensure that IRA |
| allocates registers in the order given by REG_ALLOC_ORDER even if some |
| call-saved registers appear earlier than call-used ones, this macro |
| should be defined. |
| </p></dd></dl> |
| |
| <dl> |
| <dt><a name="index-IRA_005fHARD_005fREGNO_005fADD_005fCOST_005fMULTIPLIER"></a>Macro: <strong>IRA_HARD_REGNO_ADD_COST_MULTIPLIER</strong> <em>(<var>regno</var>)</em></dt> |
| <dd><p>In some case register allocation order is not enough for the |
| Integrated Register Allocator (<acronym>IRA</acronym>) to generate a good code. |
| If this macro is defined, it should return a floating point value |
| based on <var>regno</var>. The cost of using <var>regno</var> for a pseudo will |
| be increased by approximately the pseudo’s usage frequency times the |
| value returned by this macro. Not defining this macro is equivalent |
| to having it always return <code>0.0</code>. |
| </p> |
| <p>On most machines, it is not necessary to define this macro. |
| </p></dd></dl> |
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