10.4.3 Constraint codes common to AArch32 state and AArch64 state
The following constraint codes are common to both AArch32 state and AArch64 state.
- A constant integer, or the address of a global variable or function.
- A constant integer.
Note: The immediate constraints only check that their operand is constant after
optimizations have been applied. Therefore it is possible to write code that you can
only compile at higher optimization levels. Arm recommends that
you test your code at multiple optimization levels to ensure it compiles.
- A memory reference. This constraint causes a general-purpose register to
be allocated to hold the address of the value instead of the value
itself. By default, this register is printed as the name of the register
surrounded by square brackets, suitable for use as a memory operand. For
[x7]. In AArch32 state only, you can print the register without the surrounding square brackets by using the
m template modifier. See 10.5.2 Template modifiers for AArch32 state.
- If the operand is a constant after optimizations have been performed,
this constraint is equivalent to the
i constraint. Otherwise, it is equivalent to
w constraints, depending on the type of the operand.
Note: Arm recommends that
you use more precise constraints where possible. The
does not perform any of the range checking or register restrictions that the other