Constraints

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Constraints for asm Operands

Here are specific details on what constraint letters you can use with asm 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.

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• Simple Constraints :: Basic use of constraints.
• Multi-Alternative :: When an insn has two alternative constraint-patterns.
• Modifiers :: More precise control over effects of constraints.
• Machine Constraints :: Special constraints for some particular machines.