[llvm] [FuncAttrs] Relax norecurse attribute inference (PR #139943)

[Usha Gupta via llvm-commits]

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@@ -2059,8 +2059,49 @@ static void inferAttrsFromFunctionBodies(const SCCNodeSet &SCCNodes,
   AI.run(SCCNodes, Changed);
 }
 
+/// Returns true if N or any function it (transitively) calls makes a call
+/// to an unknown external function: either an indirect call or a declaration
+/// without the NoCallback attribute.
+static bool callsUnknownExternal(LazyCallGraph::Node *N) {
+  std::deque<LazyCallGraph::Node *> Worklist;
+  DenseSet<LazyCallGraph::Node *> Visited;
+  Worklist.push_back(N);
+  Visited.insert(N);
+
+  while (!Worklist.empty()) {
+    auto *Cur = Worklist.front();
+    Worklist.pop_front();
+
+    Function &F = Cur->getFunction();
+    for (auto &BB : F) {
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usha1830 wrote:

Thanks for looking into it.
> Is there perhaps already a utility routine that can return a list of all calls made by a Function? Or could we make the same check in the loop below that looks at all the edges?

I think if I populate the edges early, I can use the calls() function instead of iterating over every instruction in every BB. I will refactor these loops.

>I took a look at CalleeInfo in llvm/include/llvm/IR/ModuleSummaryIndex.h and it doesn't have any information about callbacks, but perhaps we could add one?

Yeah. I can look at that too.

https://github.com/llvm/llvm-project/pull/139943