[llvm] [UpdateTestChecks] Don't fail silently when conflicting CHECK lines means no checks are generated for some functions (PR #159321)

[Alex Bradbury via llvm-commits]

================
@@ -918,14 +919,51 @@ def __init__(self, run_list, flags, scrubber_args, path, ginfo):
                 self._global_var_dict.update({prefix: dict()})
 
     def finish_and_get_func_dict(self):
-        for prefix in self.get_failed_prefixes():
-            warn(
-                "Prefix %s had conflicting output from different RUN lines for all functions in test %s"
-                % (
-                    prefix,
-                    self._path,
+        all_funcs = set()
+        for prefix in self._func_dict:
+            all_funcs.update(self._func_dict[prefix].keys())
+
+        warnings_to_print = collections.defaultdict(list)
+        for func in sorted(list(all_funcs)):
+            for i, run_info in enumerate(self._run_list):
+                prefixes = run_info[0]
+                if not prefixes:
+                    continue
+
+                # Check if this RUN line produces this function at all.
+                run_contains_func = True
+                for p in prefixes:
+                    if func not in self._func_dict.get(p, {}):
+                        run_contains_func = False
+                        break
----------------
asb wrote:

I've extended the comment to hopefully clarify, and also added a test case that captures this behaviour. When I thought about potential corner cases that could produce a false positive, this is the one that came to mind. Without this logic we do seem to produce a confusing warning for the `--included-generated-funcs` test case I committed. Possibly there are still cases with non-matching sets of functions and prefix clashes we would want to error, but it's not clear to me what behaviour is right. Either way, I think this patch is a strict improvement even if it's possible there are corner cases like this where _maybe_ you want even more error checking.

https://github.com/llvm/llvm-project/pull/159321