10.4.1 Constraint modifiers
All output operands require a constraint modifier. There are currently no supported constraint modifiers for input operands.
10-1 Constraint modifiers
|This operand is only written to, and only after all
input operands have been read for the last time. Therefore the
compiler can allocate this operand and an input to the same register
or memory location.
|This operand is both read from and written to.
|This operand is only written to. It might be modified before the
assembly block finishes reading the input operands. Therefore the
compiler cannot use the same register to store this operand and an
input operand. Operands with the
=& constraint modifier are known as early-clobber
Note: In the case where a register
constraint operand and a memory constraint operand are used
together, you must use the
modifier on the register constraint operand to prevent the
register from being used in the code generated to access the