Hi all,
I am trying to generate PIC code through my backend .
As per my understanding according my ISA , a global
variable is accessed using the following instructions.
/mov r0, #global variables address ;
ldw r1,r0,#0 ;( loads the global variable's value in to r1).
/If I implement PIC, ideally my PIC reg has
_GLOBAL_OFFSET_TABLE_ ( starting address of Global Offset Table) and my
global variable is some offset away from _GLOBAL_OFFSET_TABLE_. So the
code generated is /
ldw r1,pic-reg,#offset;
/In order to implement this I defined PIC_OFFSET_TABLE_REGNUM ,
LEGITIMATE_PIC_OPERAND_P (x) . My legitimate pic operand has the
constant offset range of ldw (load word )instruction. In my case my
ldw reg, reg, #K12 has maximum offset of 12 bit . So, I can address
span of 2^12.
In my md file , depending on flag flag_pic ( detecting whether PIC is
needed or not ) in movsi pattern , I emitted instruction ldw %0,
pic-reg, #offset . The
memory operand 'm' has code PLUS . Split in to REG + CONST . REG is
pic_reg and CONST is in the range of 0 - (2^12-1).
Is my understanding true?
Your help is deeply appreciated.
Thanks,
sumanth G
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