[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;
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davidtrevelyan wrote:

Thanks for the good idea. I hadn't looked before drafting this PR, but it appears like ASan solves it a similar way at one level higher - at the top level of the pass's `run` method: https://github.com/llvm/llvm-project/blob/f5742c4d540a20651a67de51e16242a52e5d4064/llvm/lib/Transforms/Instrumentation/AddressSanitizer.cpp#L1318

ThreadSanitizer has a `bool` check for whether it should `sanitizeFunction`, which returns false if there are no calls in it. MemorySanitizer does the same thing as AddressSanitizer with a `continue` at the top level if the function is `.empty()`.

If you prefer the ASan/MSan semantics I'm very happy to switch to it 👍 

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