Improvements in Tiger Compiler

• We have provided the following functions, to allow better tracking of lexically nested variables within the IR.
  • IsSameVar -
  • IsSameLevel -
  • IsLocal -
• We have delayed the insertion of register saving and loading instructions on subroutine calls to a point just before code generation. This will reduce the amount of redundant code generated.
• We have flattened the original Tree-like IR. Thus, after lowering, operands to statements may only be CONST, TEMP, NAME and MEM(exp), where an expression can be a CONST, TEMP or a binary operation of CONST's and TEMP's.

Thanks to Yung-Yu Chuang for making these improvements.