Fixes a bug in pstat module

Summary:
There was a bug in the pstat module: LNT crashes with
"UnboundLocalError: local variable 'list' referenced before assignment"
when trying to add linear regression to the regression graph.

Reviewers: cmatthews, leandron, hubert.reinterpretcast

Reviewed By: cmatthews

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D74593

Author: apolyakov

lnt/external/stats/pstat.py

@@ -182,22 +182,22 @@ def simpleabut (source, addon):
     if not isinstance(addon, (list, tuple)):
         addon = [addon]
     minlen = min(len(source), len(addon))
-    list = copy.deepcopy(source)                # start abut process
+    source_copy = copy.deepcopy(source)                # start abut process
     if not isinstance(source[0], (list, tuple)):
         if not isinstance(addon[0], (list, tuple)):
             for i in range(minlen):
-                list[i] = [source[i]] + [addon[i]]        # source/addon = column
+                source_copy[i] = [source[i]] + [addon[i]]        # source/addon = column
         else:
             for i in range(minlen):
-                list[i] = [source[i]] + addon[i]        # addon=list-of-lists
+                source_copy[i] = [source[i]] + addon[i]        # addon=list-of-lists
     else:
         if not isinstance(addon[0], (list, tuple)):
             for i in range(minlen):
-                list[i] = source[i] + [addon[i]]        # source=list-of-lists
+                source_copy[i] = source[i] + [addon[i]]        # source=list-of-lists
         else:
             for i in range(minlen):
-                list[i] = source[i] + addon[i]        # source/addon = list-of-lists
-    source = list
+                source_copy[i] = source[i] + addon[i]        # source/addon = list-of-lists
+    source = source_copy
     return source