[llvm] [IPO] Prevent removal of some convergent attr (PR #134863)

[Matt Arsenault via llvm-commits]

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@@ -1967,7 +1980,9 @@ static void inferConvergent(const SCCNodeSet &SCCNodes,
   AI.registerAttrInference(AttributeInferer::InferenceDescriptor{
       Attribute::Convergent,
       // Skip non-convergent functions.
-      [](const Function &F) { return !F.isConvergent(); },
+      [](const Function &F) {
+        return !F.isConvergent() || FunctionRequiresConvergence(F);
+      },
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arsenm wrote:

Does FunctionAttrs run in a bottom up and top down phase? Ideally we wouldn't need to inspect the users of the function, and strip convergent from call sites when possible 

https://github.com/llvm/llvm-project/pull/134863