Assignment on RTL IR Manipulation

Problem Statement

1. Traverse the RTL level CFG


2. Print a more understandable RTL code by using "=" for set operations, converting prefix expressions into infix, and using familiar symbols for operations. Ignore non-instruction organisational rtx's like NOTE insns.

Example:

For the following two rtl instructions :

(insn 5 4 6 3 1.c:15 (set (reg:SI 59)
(mem/c/i:SI (plus:SI (reg/f:SI 54 virtual-stack-vars)
(const_int -8 [0xfffffff8])) [0 b+0 S4 A32])) -1 (nil))

(insn 6 5 7 3 1.c:15 (set (reg:SI 61)
(mem/c/i:SI (plus:SI (reg/f:SI 54 virtual-stack-vars)
(const_int -4 [0xfffffffc])) [0 a+0 S4 A32])) -1 (nil))

(insn 7 6 8 3 1.c:15 (parallel [
(set (reg:SI 60)
(plus:SI (reg:SI 61)
(reg:SI 59)))
(clobber (reg:CC 17 flags))
]) -1 (nil))



Generate the following:

r59 = *(r54 - 8)
r61 = *(r54 - 4)
r60 = r61 + r59 || clobber r17

Hints:

A. Possible approach:

1. Take a very simple program, eg.
   main()
   {
   int a,b,c;
   c = a + b;
   }
   
2. Generate the rtl dump by executing gcc. Inspect the rtl dump of pass_expand.
3. Extend the base code to handle rtl objects appearing in the rtl dump of the above program.
4. Handle other rtl objects.

B. Solution hint:

Use recursion. Trying modifying the base code.

Debugging AID: use GET_RTX_NAME(int rxt_code) to print the ascii string describing the rtl object you are currently processing.

Anticipated Problems:

1. The most important macros needed are:
   GET_CODE
   GET_RTX_NAME
   Accessor functions, XINT, XEXP,XSTR,XVEC


2. What are The CODES of the RTL objects? Handle these cases first:
   PLUS, MINUS, MUL, DIV
   GE,LE,GT...
   NEG, NOT
   SET
   MEM, REG
   CONST_INT
   SYMBOL_REF, LABEL_REF, CODE_LABEL
   PC,COMPARE,IF_THEN_ELSE
   USE,CC0