def gen(self, context: Context, target: str):
"""Translate 'while' loop into explicit jumps.
"""
loop_head = context.new_label("loop")
loop_exit = context.new_label("endloop")
context.add_line("{}: #While loop".format(loop_head))
reg = context.alloc_reg()
self.cond.gen(context, target=reg)
# Is it zero?
context.add_line("\tSUB r0,{},r0 ".format(reg))
context.add_line("\tJUMP/Z {}".format(loop_exit))
context.free_reg(reg)
self.expr.gen(context, target)
context.add_line("\tJUMP {}".format(loop_head))
context.add_line("{}: ".format(loop_exit))
def gen(self, context: Context, target: str):
"""
Generate code for an if/else.
"""
# The outline of the code you should generate is:
# <code for expression>
# subtract expression result from zero
# if zero, jump to elsepart
# <code for 'then' part>
# jump to endif
# elsepart:
# <code for elsepart>
# fi:
# Generate fresh labels for the 'elsepart' and 'fi' each time,
# since there could be more than one 'if' statement in a program.
# Look at the 'while' statement above for examples of code
# generation for tests, jumps, and labels.
#
# Example:
# if 10 - 9: ---> condition
# ------
# x = 5 ---> then
# else:
# x = 0 ---> else
# initialize labels and registers
elsepart = context.new_label("else")
fi = context.new_label("end else")
reg = context.alloc_reg()
self.cond.gen(context, target=reg) # generate condition
# If part
# Is it zero?
context.add_line("\tSUB r0,{},r0 ".format(reg))
context.add_line("\tJUMP/Z {}".format(elsepart))
self.thenpart.gen(context, target) # generate then part
context.add_line("JUMP {}".format(fi))
# Else part
context.add_line("{}: #Else loop".format(elsepart))
self.elsepart.gen(context, target) # generate else part
context.add_line("{}".format(fi))
context.free_reg(reg) # free the register