Add conditional branching.

stepper.py

@@ -12,6 +12,11 @@ def err(msg):
           .format(msg))
 
 
+def warn(msg):
+    print('WARNING: {}'
+          .format(msg))
+
+
 def step(insns, terminator, blocks, stack_frames, ssa_env, global_env, memory,
          tdecs, fdecs, call_res):
     if len(insns) == 0:
@@ -108,6 +113,30 @@ def terminate(terminator, blocks, stack_frames, ssa_env, global_env, memory):
         print('Jumping unconditionally to {}'
               .format(label))
 
+        return (new_insns, new_terminator, blocks, stack_frames,
+                ssa_env, memory, None)
+    elif isinstance(terminator, ll.Cbr):
+        ty = terminator.ty
+        if ty != ll.SimpleType.I1:
+            warn('Branching based on value of type {}. You ought to branch on {}'
+                 .format(ll.ty2s(ty), ll.ty2s(ll.SimpleType.I1)))
+        operand = terminator.oper
+        operand_v = eval_oper(operand, ssa_env, global_env)
+
+        if operand_v:
+            label = terminator.then_label
+        else:
+            label = terminator.else_label
+
+        next_block = blocks[label]
+        new_insns = next_block.insns
+        new_terminator = next_block.terminator
+        clear_block_from_ssa_env(new_insns, ssa_env)
+
+        # TODO
+        print('Operand was {}. Branching to {}'
+              .format(operand_v, label))
+
         return (new_insns, new_terminator, blocks, stack_frames,
                 ssa_env, memory, None)
     else:
@@ -182,14 +211,14 @@ def gogo():
     data = r'''
 define i64 @tigermain (i64 %U_mainSL_8, i64 %U_mainDummy_9) {
     %a = add i64 3, 5 ; please be 8
-    br label %L1
+    %c = icmp eq i64 %a, 9
+    br i1 %c, label %L1, label %L2
 L1:
     %b = add i64 %a, %a
-    %c = icmp eq i64 %a, %b
     ret i1 %c
 L2:
     %d = add i64 %a, 1
-    %e = add i64 10, %b
+    %e = add i64 10, %d
     ret i64 %e
 }
 '''