[llvm] [rtsan] Handle attributed IR function declarations (PR #169577)

[via llvm-commits]

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@@ -61,23 +61,21 @@ static void insertCallAtAllFunctionExitPoints(Function &Fn,
       insertCallBeforeInstruction(Fn, I, InsertFnName, FunctionArgs);
 }
 
-static PreservedAnalyses rtsanPreservedCFGAnalyses() {
-  PreservedAnalyses PA;
-  PA.preserveSet<CFGAnalyses>();
-  return PA;
-}
+static void runSanitizeRealtime(Function &Fn) {
+  if (Fn.empty())
+    return;
 
-static PreservedAnalyses runSanitizeRealtime(Function &Fn) {
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davidtrevelyan wrote:

Perhaps! But the issue is we're already not returning these preserved analyses - they're sadly discarded at the moment. I would advocate for this NFC change because it makes the current behaviour explicit - even if it's not correct. I bundled this change in with this PR because it made the implementation of the checking a bit easier, but I'd be happy to submit this in a separate preparatory PR first - if that's easier to follow - just let me know. 

https://github.com/llvm/llvm-project/pull/169577