Fix function calls yielding 'None' as register where 'R0' should be placed

1 files changed, 19 insertions, 0 deletions

diff --git a/pp2cc.py b/pp2cc.py
index db1886e..35b208b 100755
--- a/pp2cc.py
+++ b/pp2cc.py
@@ -72,12 +72,31 @@ class Registers(object):
             return text
         # out of luck
         return None
+    def get_instruction(self, text):
+        """Retrieve the instruction from text skipping labels and comments"""
+        text = text.strip()
+        # ignore commented lines
+        if text.startswith(";"):
+            return None
+        # skip labels if any
+        text = text.upper().split(":", 1)[-1]
+        # the first element is assumed to be an instruction
+        text = text.lstrip(" ").split(" ", 1)[0]
+        # instructions have a length between 2 (OR) and 4 (LOAD)
+        if len(text) >= 2 and len(text) <= 4:
+            return text
+        return None
     def find_register(self, instructions_list, fatal=False):
         """Finds the last modified register in a list of instructions"""
         for line in reversed(instructions_list):
             reg = self.get_register(line)
             if reg:
                 return reg
+            else:
+                instruction = self.get_instruction(line)
+                # convention: non-void functions store their result value in R0
+                if instruction == "BRS":
+                    return "R0"
         if fatal:
             raise RuntimeError("No register found in instructions list")
         return None