The type of an expression used in place of an ARM integer register must be either an
integral type (that is,
long long, or a pointer type. No sign extension is performed
short types. You must perform
sign extension explicitly for these types. The compiler might add code to evaluate these
expressions and allocate them to registers.
When an operand is used as a destination, the expression must be a modifiable lvalue if
used as an operand where the register is modified. For example, a destination register or a
base register with a base-register update.
For an instruction containing more than one expression operand, the order that expression
operands are evaluated is unspecified.
An expression operand of a conditional instruction is only evaluated if the conditions for
the instruction are met.
A C or C++ expression that is used as an inline assembly code operand might
result in the instruction being expanded into several instructions. This happens if the
value of the expression does not meet the constraints set out for the instruction operands
in the ARM Architecture Reference Manual.
If an expression used as an operand creates a temporary that requires destruction, then the
destruction occurs after the inline assembly instruction is executed. This is analogous to
the C++ rules for destruction of temporaries.
A simple expression operand is one of the following:
Any expression containing one of the following is not a simple expression operand:
An implicit function call, such as for division, or explicit function call.
The construction of a C++ temporary.
An arithmetic or logical operation.