《东南大学编译原理课件Cp8.ppt

Chapter 8 Intermediate Code Generation Zhai Yuqing Zhou Xiaoyu Overview Position of Intermediate Code Generator Implementation of Intermediate Code Generator Syntax-directed translation, folded into parsing Intermediate Representations Syntax tree Postfix notation Three-address code Quadruple Benefits for Using a Machine-independent Intermediate Form A machine-independent code optimizer can be applied to the intermediate representation. Three-address Code (TAC) Three-address Code (TAC) A sequence of statements of the general form x= y op z. There is only one operator on the right side of a statement. Here, x , y, z are names, constants, or compiler-generated temporaries; op stands for any operator. Three-address Code (TAC) Each three-address code statement contains three addresses, two for the operands and one for the result. Three address code is a linearized representation of a syntax tree. Types of TAC X=y op z X=op y X=y goto L if x relop y goto L param x call p, n return y Types of TAC x=y[i] x[i]=y x=y /*value of x is the location of y*/ x=*y *x=y Syntax-directed Translation into TAC We can use S-attributed definition to generate three-address code for assignment statement. We create a new name every time a temporary is needed. Quadruples Implementations of Three-address Statements A three-address statement is an abstract form of intermediate codes Quadruples (op, arg1, arg2, result) Triples (n) (op,arg1,arg2) (m) (op,(n),arg) Advantages of Quadruples Good for optimizing Assignment Statements functions NEWTEMP() GEN(OP, ARG1, ARG2, RESULT) Semantic Rules for Quadruple Code Generation Semantic Rules for Quadruple Code Generation Addressing Array Elements Addressing Array Elements One-dimensional array Addr(A[i]) = base + (i - low) * w = i*w + (base – low * w) Here, we assume the width of each array element is w and the start address of the array block is base. Addressing Array Elements The array i