TAC

This handout summarizes a simple TAC intermediate language. There are many choices as to the exact instructions to include in such a language, and you will probably want to modify and extend this variant when we translate IC programs into TAC.

One representation note: TAC operands that name program variables should refer to the symbol-table entries you built in PA 2, not to raw identifier strings, so that distinct variables with the same name stay distinct.

Instruction Forms

• Arithmetic and Logic Instructions.  
  The basic instruction forms are:

          a = b OP c          a = OP b

  where OP can be  
     

  an arithmetic operator:	ADD, SUB, DIV, MUL
  a logic operator:	AND, OR, XOR
  a comparison operator:	EQ, NEQ, LE, LEQ, GE, GEQ
  a unary operator:	MINUS, NEG

• Data Movement Instructions. 
  

  Copy:	a = b
  Load/store:	a = *b	*a = b
  Array load/store:	a = b[i]	a[i] = b
  Field load/store:	a = b.f	a.f = b

• Branch Instructions.  
  

  Label:	label L
  Unconditional jump:	jump L
  Conditional jump:	cjump a L	(jump to L if a is true)

• Function Call Instructions. 
  

  Call with no result:	call f(a_1, ..., a_n)
  Call with result:	a = call f(a_1, ..., a_n)

  (Note: there is no explicit TAC representation for parameter passing, stack frame setup, etc.)