From 32294d4d84b6800fc7dd8bcbf15a5628f33b4eda Mon Sep 17 00:00:00 2001
From: Jana Rekittke <jana@rekittke.name>
Date: Tue, 7 Jul 2009 13:42:52 +0200
Subject: some more comments

---
 src/back/generator.py | 17 +++++++++++------
 1 file 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:
-- 
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