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| <h3 class="section">6.42 Constraints for <code>asm</code> Operands</h3> |
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| <p><a name="index-operand-constraints_002c-_0040code_007basm_007d-2809"></a><a name="index-constraints_002c-_0040code_007basm_007d-2810"></a><a name="index-g_t_0040code_007basm_007d-constraints-2811"></a> |
| Here are specific details on what constraint letters you can use with |
| <code>asm</code> operands. |
| Constraints can say whether |
| an operand may be in a register, and which kinds of register; whether the |
| operand can be a memory reference, and which kinds of address; whether the |
| operand may be an immediate constant, and which possible values it may |
| have. Constraints can also require two operands to match. |
| Side-effects aren't allowed in operands of inline <code>asm</code>, unless |
| ‘<samp><span class="samp"><</span></samp>’ or ‘<samp><span class="samp">></span></samp>’ constraints are used, because there is no guarantee |
| that the side-effects will happen exactly once in an instruction that can update |
| the addressing register. |
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| <ul class="menu"> |
| <li><a accesskey="1" href="Simple-Constraints.html#Simple-Constraints">Simple Constraints</a>: Basic use of constraints. |
| <li><a accesskey="2" href="Multi_002dAlternative.html#Multi_002dAlternative">Multi-Alternative</a>: When an insn has two alternative constraint-patterns. |
| <li><a accesskey="3" href="Modifiers.html#Modifiers">Modifiers</a>: More precise control over effects of constraints. |
| <li><a accesskey="4" href="Machine-Constraints.html#Machine-Constraints">Machine Constraints</a>: Special constraints for some particular machines. |
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