[-Wunsafe-buffer-usage] Add AST info to the unclaimed DRE debug notes for analysis

- For a better understand of what the unsupported cases are, we add
  more information to the debug note---a string of ancestor AST nodes
  of the unclaimed DRE. For example, an unclaimed DRE p in an
  expression `*(p++)` will result in a string starting with
  `DRE ==> UnaryOperator(++) ==> Paren ==> UnaryOperator(*)`.

- To find out the most common patterns of those unsupported use cases,
  we add a simple script to build a prefix tree over those strings and
  count each prefix. The script reads input line by line, assumes a
  line is a list of words separated by `==>`s, and builds a prefix tree
  over those lists.

Reviewed by: t-rasmud (Rashmi Mudduluru), NoQ (Artem Dergachev)

Differential revision: https://reviews.llvm.org/D158561

1 files changed, 39 insertions, 0 deletions

diff --git a/clang/utils/analyze_safe_buffer_debug_notes.py b/clang/utils/analyze_safe_buffer_debug_notes.py
new file mode 100644
index 0000000..f0a6e4d
--- /dev/null
+++ b/clang/utils/analyze_safe_buffer_debug_notes.py
@@ -0,0 +1,39 @@
+import sys
+from collections import OrderedDict
+
+class Trie:
+    def __init__(self, name):
+        self.name = name
+        self.children = OrderedDict()
+        self.count = 1
+
+    def add(self, name):
+        if name in self.children:
+            self.children[name].count += 1
+        else:
+            self.children[name] = Trie(name)
+        return self.children[name]
+
+    def print(self, depth):
+        if depth > 0:
+            print('|', end="")
+        for i in range(depth):
+            print('-', end="")
+        if depth > 0:
+            print(end=" ")
+        print(self.name, '#', self.count)
+        for key, child in self.children.items():
+            child.print(depth + 1)
+
+
+Root = Trie("Root")
+
+if __name__ == "__main__":
+    for line in sys.stdin:
+        words = line.split('==>')
+        words = [word.strip() for word in words]
+        MyTrie = Root;
+        for word in words:
+            MyTrie = MyTrie.add(word)
+
+    Root.print(0)