[llvm] [MemProf] Fix assert when exists direct recursion (PR #78264)

[Teresa Johnson via llvm-commits]

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@@ -3472,15 +3472,19 @@ bool MemProfContextDisambiguation::applyImport(Module &M) {
             assert(StackMDNode);
             SmallVector<unsigned> StackIdsFromMetadata;
             CallStack<MDNode, MDNode::op_iterator> StackContext(StackMDNode);
-            for (auto ContextIter =
-                     StackContext.beginAfterSharedPrefix(CallsiteContext);
+            auto ContextIterBegin =
+                StackContext.beginAfterSharedPrefix(CallsiteContext);
+            uint64_t LastStackContextId = *ContextIterBegin == UINT64_MAX
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teresajohnson wrote:

Or maybe use value 0, or 1 if the first context id happens to be 0. I think that would be clearer than using value + or - 1 depending on whether it is max uint. Regardless, please add a comment about what we're trying to do (skip the checking on the first iteration).

https://github.com/llvm/llvm-project/pull/78264