diff options
| -rw-r--r-- | src/back/generator.py | 17 |
1 files changed, 11 insertions, 6 deletions
diff --git a/src/back/generator.py b/src/back/generator.py index 1ae403f..84ab639 100644 --- a/src/back/generator.py +++ b/src/back/generator.py @@ -33,6 +33,8 @@ class Generator(object): else: self.__op_list.append(op) + # this cde will appear before every function + # sets bp, pushes used registers and variables def generate_prologue(self, name): Scope().set_function(name) self.emit(Label(name)) @@ -43,6 +45,8 @@ class Generator(object): for register in Register().get_registers(name): self.emit("PUSH r%d" % register) + # this code will appear after every function + # restores registers, sp, bp def generate_epilogue(self, name): for variable in Scope().get_variables()[1]: self.emit("POP r0") @@ -55,7 +59,7 @@ class Generator(object): self.emit("RET") def generate(self): - # pass 1 - generate non-label ops + # pass 1 - generate ops, but not labels yet for tac in self.tac_list: if isinstance(tac, TAC): if tac.op in [Op.ADD, Op.SUB, Op.MUL, Op.DIV, Op.MOD, Op.AND, Op.OR]: @@ -106,7 +110,7 @@ class Generator(object): else: raise Exception("%s is not a valid TACList element" % repr(tac)) - # pass 2 - generate label ops + # pass 2 - generate label ops (ignores still present labels) for op in self.__op_list: if isinstance(op, TAC): if op.op == Op.BEZ: @@ -125,12 +129,12 @@ class Generator(object): # pass 3 - remove labels self.__op_list = filter(lambda x: not isinstance(x, Label), self.__op_list) - # pass 4 - replace pseudo registers and insert number of registers + # pass 4 - replace the pseudo registers with their register numbers def replace_pseudo_regs(op): regs = Register().count - bp = "r%d" % (regs + 1) - sp = "r%d" % (regs + 2) - rv = "r%d" % (regs + 3) + bp = "r%d" % (regs + 1) # base pointer + sp = "r%d" % (regs + 2) # stack pointer + rv = "r%d" % (regs + 3) # return value return op.replace("bp", bp).replace("sp", sp).replace("rv", rv) self.__op_list = map(replace_pseudo_regs, self.__op_list) @@ -139,6 +143,7 @@ class Generator(object): # finally, print the generated code print "\n".join(self.__op_list) + # find the line number to which the given label leads def get_label_offset(self, name, tac): tac_index = 0 for op in self.__op_list: |