Referring to Variables in Instruction Operands

For instructions that require register operands, (such as the add instruction), global variables, function parameters, and local variables must be declared with the keyword register .

Using C Variables with Instructions that Require Register Operands shows inline assembly language statements that correctly use C-language variables as operands in instructions that require register operands.

int my_global asm("r14")= 25; /* global variable */
int my_loc asm("r15")= 1; 
asm void red(register int *my_param)
{
register int result;
fralloc
add result, r4, my_global /* line 10 */
add result, my_global, my_param /* line 11 */
add result, my_param, my_loc /* line 12 */
frfree
blr
}

In Using C Variables with Instructions that Require Register Operands, the statement on line 10, 11, and 12 are all correct because their operands are all declared with the register keyword.