optimise_deadcode.py

#-------------------------------------------------------------------------------
# Name:         optimise_deadcode.py
# Purpose:      Remove dead code, like stmts after return, unreachable code
#
# Author:       David Sverdlov
# Course:       Compilers, june 2015
#-------------------------------------------------------------------------------
from node import *

VERBOSE = True
def printt(*args):
    if VERBOSE:
        for a in args:
            print " - " + a

# right now only detects code after a return statement,
# expand with double assignment removal x=2; x=3
def flatten(x):
    result = []
    for el in x:
        if hasattr(el, "__iter__") and not isinstance(el, basestring):
            result.extend(flatten(el))
        else:
            result.append(el)
    return result

def optimise_dead_code(ast):
    dead_code = []
    if not(type(ast) is Node) or ast.is_empty() or ast.is_leaf():
        return dead_code
    else:
        return_found = False
        for child in ast.children:
            if (type(child) is Node) and (child.data == 'return') and not(return_found):
                return_found = True
            else:
                if return_found: # return already appeared son
                    dead_code.append(child)
                    printt("Deleting dead code: " + child.toString())
                    ast.children.remove(child)

            opt_child = optimise_dead_code(child)
            if(opt_child != []):
                dead_code.append(opt_child)


    return flatten(dead_code)