bench: add validate_csmith

Check that a csmith-generated file is interresting enough to be worth
keeping and compiling.

benching/csmith/.gitignore

@@ -0,0 +1 @@
+tests/

benching/csmith/validate_csmith.py

@@ -0,0 +1,112 @@
+#!/usr/bin/env python3
+
+""" Checks whether a Csmith-generated file is complicated enough
+
+This does not parse C code, but performs only string lookups. In particular, it
+assumes functions are named `func_[0-9]+` or `main`, and that a function
+implementation is of the form (whitespaces meaningful)
+
+(static)? RETURN_TYPE func_[0-9]+(.*)
+{
+    ...
+}
+"""
+
+import sys
+import re
+
+
+def build_graph(prog):
+    func_declare_re = re.compile(r'(?:static )?\S.* (func_\d+|main) ?\(.*\)$')
+    func_call_re = re.compile(r'func_\d+')
+
+    graph = {}
+    cur_function = None
+
+    for line in prog:
+        func_declare_groups = func_declare_re.match(line)
+        if func_declare_groups:
+            func_name = func_declare_groups.group(1)
+            cur_function = func_name
+            graph[func_name] = []
+
+        elif line == '}':
+            cur_function = None
+
+        else:
+            if cur_function is None:
+                continue  # Not interresting outside of functions
+
+            last_find_pos = 0
+            call_match = func_call_re.search(line, pos=last_find_pos)
+
+            while call_match is not None:
+                graph[cur_function].append(call_match.group(0))
+                last_find_pos = call_match.end()
+                call_match = func_call_re.search(line, pos=last_find_pos)
+
+    reachable = set()
+    def mark_reachable(node):
+        nonlocal reachable, graph
+        if node in reachable:
+            return
+        reachable.add(node)
+
+        for child in graph[node]:
+            mark_reachable(child)
+    mark_reachable('main')
+
+    delete = []
+    for node in graph:
+        if node not in reachable:
+            delete.append(node)
+    for node in delete:
+        graph.pop(node)
+
+    return graph
+
+
+def get_depth(graph):
+    entry_point = 'main'
+
+    depth_of = {}
+    def find_depth(node):
+        nonlocal depth_of
+
+        if node in depth_of:
+            return depth_of[node]
+
+        callees = graph[node]
+        if callees:
+            depth = max(map(find_depth, callees)) + 1
+        else:
+            depth = 1
+        depth_of[node] = depth
+        return depth
+
+    return find_depth(entry_point)
+
+
+def get_prog_lines():
+    def do_read(handle):
+        return handle.readlines()
+
+    if len(sys.argv) > 1:
+        with open(sys.argv[1], 'r') as handle:
+            return do_read(handle)
+    else:
+        return do_read(sys.stdin)
+
+
+def main():
+    prog = get_prog_lines()
+    graph = build_graph(prog)
+
+    if len(graph) < 5 or get_depth(graph) < 5:
+        print("Graph is too simple.", file=sys.stderr)
+        sys.exit(1)
+    sys.exit(0)
+
+
+if __name__ == '__main__':
+    main()