Fix if-else regs

tools/cc.py

@@ -186,6 +186,15 @@ class RegBank:
         if var1 is not None:
             self.loaded(var1, reg0)
 
+    def snap(self):
+        return dict(self.vars), dict(self.cleanup)
+
+    def restore(self, snap):
+        self.reset()
+        vardict, cleanup = snap
+        for var, reg in vardict.items():
+            self.loaded(var, reg, cleanup=cleanup.get(reg, None))
+
     @contextlib.contextmanager
     def borrow(self, howmany):
         regs = [self.take() for i in range(howmany)]
@@ -775,8 +784,10 @@ class CcInterp(lark.visitors.Interpreter):
         has_else = len(tree.children) > 2
         op = IfOp(self.cur_fun, [tree.children[0].op.out, mark, has_else])
         self._synth(op)
+        begin_vars = self.cur_fun.regs.snap()
         self.visit(tree.children[1])
         if has_else:
+            self.cur_fun.regs.restore(begin_vars)
             self.cur_fun.ops.append(op.synth_else)
             self.visit(tree.children[2])
         self.cur_fun.ops.append(op.synth_endif)