Abstract Syntax Trees The Abstract Syntax Tree (AST) - Polaris

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if statement a l condition then-part relation statement list l relop r 1 s(1) s(2) < assignment stmt op r + 1 lhs rhs x l op r x + 1 ... Simple Code Generation (From Compilers. Principles, Techniques, and Tools by A. Aho, R. Sethi, and J. Ullman). 3 4
Three address representation Program Flow Graph Source-to-source transformations may be applied to the AST. The next step is to generate low-level code, usually three address code. In many cases, the compound statements (e.g. for or do loops and if statements) are transformed into sequences of instructions which include three-address operations as well as cmp and jump instructions. The original structure of the program (e.g. loops ) is recovered by analyzing the program flow graph. In some cases (e.g. SUIF) information on the high-level constructs is kept as annotations to the three address representation of the program. A program flow graph is also necessary for compilation. the nodes are the basic blocks. There is an arc from block B 1 to block B 2 if B 2 can follow B 1 in some execution sequence. A basic block is a sequence of consecutive statements in which flow of control enters at the beginning and leaves at the end without halts or possibility of branching except at the end. Algorithm BB: Basic Block Partition Input: A program PROG in which instructions are numbered in sequence from 1 to |PROG|. INST(i) denotes the ith instruction. Output 1.the set of LEADERS of initial block instructions. 2.for all x in LEADERS, the set BLOCK(x) of all intructions in the block beginning at x 3.Method: 5 6
Page 1: The Abstract Syntax Tree (AST) An a
Page 5 and 6: Target Machine Language Algorithm S
Page 7 and 8: NEXTUSE and LIVEONEXIT getreg(y,I)
Page 9 and 10: Algorithm DAG: Constructing a DAG I
Page 11 and 12: A Heuristic Ordering for DAGs A sim
Page 13: gencode(n): Another technique to im

Abstract Syntax Trees The Abstract Syntax Tree (AST) - Polaris

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