Fix some mypy errors.

It looks like mypy 0.560 doesn't like when a local variable changes its
type inside a function.

Fixes introduce a new variable instead of reusing an existing one.

lib/cretonne/meta/cdsl/instructions.py

@@ -290,12 +290,12 @@ class Instruction(object):
         # Allow a single Operand instance instead of the awkward singleton
         # tuple syntax.
         if isinstance(x, Operand):
-            x = (x,)
+            y = (x,)  # type: Tuple[Operand, ...]
         else:
-            x = tuple(x)
-        for op in x:
+            y = tuple(x)
+        for op in y:
             assert isinstance(op, Operand)
-        return x
+        return y
 
     @staticmethod
     def _to_constraint_tuple(x):
@@ -307,12 +307,12 @@ class Instruction(object):
         # import placed here to avoid circular dependency
         from .ti import TypeConstraint  # noqa
         if isinstance(x, TypeConstraint):
-            x = (x,)
+            y = (x,)  # type: Tuple[TypeConstraint, ...]
         else:
-            x = tuple(x)
-        for op in x:
+            y = tuple(x)
+        for op in y:
             assert isinstance(op, TypeConstraint)
-        return x
+        return y
 
     def bind(self, *args):
         # type: (*ValueType) -> BoundInstruction

lib/cretonne/meta/unique_table.py

@@ -62,16 +62,19 @@ class UniqueSeqTable:
         """
         if len(seq) == 0:
             return 0
-        seq = tuple(seq)
-        if seq in self.index:
-            return self.index[seq]
+        tseq = tuple(seq)
+        if tseq in self.index:
+            return self.index[tseq]
 
         idx = len(self.table)
-        self.table.extend(seq)
+        self.table.extend(tseq)
 
         # Add seq and all sub-sequences to `index`.
-        for length in range(1, len(seq) + 1):
-            for offset in range(len(seq) - length + 1):
-                self.index[seq[offset:offset+length]] = idx + offset
+        index = self.index  # type: Dict[Tuple[Any, ...], int]
+        assert index is not None
+        for length in range(1, len(tseq) + 1):
+            for offset in range(len(tseq) - length + 1):
+                key = tseq[offset:offset+length]
+                index[key] = idx + offset
 
         return idx