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<h4 class="subsection">6.43.3 Constraints for <code>asm</code> Operands</h4>
<p><a name="index-operand-constraints_002c-_0040code_007basm_007d-3433"></a><a name="index-constraints_002c-_0040code_007basm_007d-3434"></a><a name="index-g_t_0040code_007basm_007d-constraints-3435"></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.
<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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