diff --git a/ll.py b/ll.py
index 4e4bd88..f6928d6 100644
--- a/ll.py
+++ b/ll.py
@@ -107,6 +107,9 @@ def insn2s(insn):
         return ('{} {} {}, {}'
                 .format(insn.bop, ty2s(insn.ty),
                         oper2s(insn.left), oper2s(insn.right)))
+    if isinstance(insn, Alloca):
+        return ('alloca {}'
+                .format(ty2s(insn.ty)))
     elif isinstance(insn, Icmp):
         return ('icmp {} {} {}, {}'
                 .format(insn.cnd, ty2s(insn.ty),
@@ -134,6 +137,7 @@ def insn2s(insn):
         # TODO
         print('insn2s: Unknown insn: {}'
               .format(insn))
+        return '???'
 
 def terminator2s(terminator):
     if isinstance(terminator, Ret):
diff --git a/stepper.py b/stepper.py
index 6d63e02..769c2df 100644
--- a/stepper.py
+++ b/stepper.py
@@ -3,7 +3,7 @@ import parser
 
 
 def TODO(msg):
-    print('TODO, not implemented yet at {}'
+    print('TODO: not implemented yet at {}'
           .format(msg))
 
 
@@ -17,6 +17,9 @@ def warn(msg):
           .format(msg))
 
 
+GARBAGE = '<<Unitialized memory>>'
+
+
 def step(insns, terminator, blocks, stack_frames, ssa_env, global_env, memory,
          tdecs, fdecs, call_res):
     if len(insns) == 0:
@@ -42,7 +45,18 @@ def step(insns, terminator, blocks, stack_frames, ssa_env, global_env, memory,
         print('{} {}, {}'
               .format(bop, left_v, right_v))
     elif isinstance(next_insn, ll.Alloca):
-        TODO('Alloca')
+        ty = next_insn.ty
+        base_ty = ty2base_ty(ty, tdecs)
+        size = base_ty2size(base_ty)
+
+        # TODO
+        print('alloca {}  -->  allocating {} cells'
+              .format(ll.ty2s(base_ty), size))
+
+        ptr = len(memory)
+        for i in range(max(size, 1)):
+            memory.append(GARBAGE)
+        res = ptr
     elif isinstance(next_insn, ll.Load):
         TODO('Load')
     elif isinstance(next_insn, ll.Store):
@@ -287,23 +301,36 @@ def eval_icmp(cnd, left, right):
         return 0
 
 
+def ty2base_ty(ty, tdecs):
+    if isinstance(ty, ll.SimpleType):
+        return ty
+    elif isinstance(ty, ll.PointerType):
+        return ll.PointerType(ty2base_ty(ty.inner_ty))
+    else:
+        # TODO
+        err('ty2base_ty: Unknown type: {}'
+            .format(ll.ty2s(ty)))
+        return ty
+
+
+def base_ty2size(base_ty):
+    if isinstance(base_ty, ll.SimpleType):
+        return 1
+    else:
+        # TODO
+        err('base_ty2size: Unknown type or illegal type: {}'
+            .format(ll.ty2s(base_ty)))
+        return 1
+
+
 def gogo():
     p = parser.LLVMParser()
     p.build()
     data = r'''
 define i64 @tigermain (i64 %U_mainSL_8, i64 %U_mainDummy_9) {
-    %a = add i64 3, 5 ; please be 8
-    %c = icmp eq i64 %a, 8
-    br i1 %c, label %L1, label %L1
-L1:
-    %b = call i64 @f (i64 7, i64 %a)
-    ret i1 %c
-}
-
-define i64 @f (i64 %x, i64 %y) {
-    %a = mul i64 2, %y
-    %b = mul i64 %x, %a
-    ret i64 %b
+    %a = alloca i64
+    %b = alloca i64
+    ret i64 77
 }
 '''