Fix some Concat tests

mythril/laser/smt/bitvec_helper.py

@@ -1,6 +1,6 @@
 from typing import Union, overload, List, Set, cast, Any, Callable
 import z3
-
+from copy import copy
 from mythril.laser.smt.bool import Bool, Or
 from mythril.laser.smt.bitvec import BitVec, BitVecExtract
 from mythril.laser.smt.bitvecfunc import BitVecFunc
@@ -83,8 +83,7 @@ def UGE(a: BitVec, b: BitVec) -> Bool:
     """Create an unsigned greater or equals expression.
 
     :param a:
-    :param b:/home/nikhil/Work/Mythril/mythril2/mythril/laser/smt/bitvec_helper.py", line 154, in Concat
+    :param b:
-    or bv.parent
     :return:
     """
     return Or(UGT(a, b), a == b)
@@ -146,26 +145,33 @@ def Concat(*args: Union[BitVec, List[BitVec]]) -> BitVec:
             nested_functions += bv.nested_functions
             nested_functions += [bv]
     new_bvs = []
-    prev_bv = bvs[0]
+    prev_bv = copy(bvs[0])
-    # casting everywhere in if's looks quite messy, so I am type ignoring
+
+    # casting everywhere in "if's" will look quite messy, so I am type ignoring them.
     for bv in bvs[1:]:
         if (
             not check_extracted_var(bv)
             or bv.high + 1 != prev_bv.low  # type: ignore
             or z3.simplify(bv.parent.raw != prev_bv.parent.raw)  # type: ignore
         ):
+
             if check_extracted_var(prev_bv) and hash(prev_bv) == hash(
-                prev_bv.parent
+                prev_bv.parent  # type: ignore
-            ):  # type: ignore
+            ):
                 new_bvs.append(prev_bv.parent)  # type: ignore
             else:
                 new_bvs.append(prev_bv)
-            prev_bv = bv
+            prev_bv = copy(bv)
             continue
         prev_bv.raw = z3.Concat(prev_bv.raw, bv.raw)
-        prev_bv.low = bv.low
+        prev_bv.low = bv.low  # type: ignore
-
+    if check_extracted_var(prev_bv) and hash(z3.simplify(prev_bv.raw)) == hash(
+        prev_bv.parent  # type: ignore
+    ):
+        prev_bv = prev_bv.parent  # type: ignore
     new_bvs.append(prev_bv)
+    if len(new_bvs) == 1:
+        return prev_bv
     if nested_functions:
         return BitVecFunc(
             raw=nraw,
@@ -174,6 +180,7 @@ def Concat(*args: Union[BitVec, List[BitVec]]) -> BitVec:
             nested_functions=nested_functions,
             concat_args=new_bvs,
         )
+
     return BitVec(raw=nraw, annotations=annotations, concat_args=new_bvs)
 
 
@@ -217,9 +224,11 @@ def Extract(high: int, low: int, bv: BitVec) -> BitVec:
         bv.simplify()
         if check_extracted_var(val) and hash(val.raw) == hash(val.parent.raw):
             val = val.parent
+        assert val.size() == high - low + 1
         return val
     input_string = ""
     bv.simplify()
+    assert raw.size() == high - low + 1
     if isinstance(bv, BitVecFunc):
         return BitVecFuncExtract(
             raw=raw,