Hello, I have some questions about code reordering and 'asm volatile("" :::
"memory");'
>From gcc docs: 'The "memory" clobber tells the compiler that the assembly
code performs memory reads or writes to items other than those listed in
the input and output operands (for example, accessing the memory pointed to
by one of the input parameters). To ensure memory contains correct values,
GCC may need to flush specific register values to memory before executing
the asm. Further, the compiler does not assume that any values read from
memory before an asm remain unchanged after that asm; it reloads them as
needed. Using the "memory" clobber effectively forms a read/write memory
barrier for the compiler.'
Does this mean that all data could be accessed including global variables,
data in heap and local variables? Or is it not true for local variables?
For example:
int local = 5;
asm volatile("" ::: "memory");
local += 6;
Could it be reordered in the following way (because 'local' is local
variable and could not be accessed):
int local = 5;
local += 6;
asm volatile("" ::: "memory");
Could 'local' be optimized out in this case?
Thank you,
Airat Gaskarov
