[llvm] [GVN] Look through select/phi when determining underlying object (PR #99509)

[Florian Hahn via llvm-commits]

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@@ -6609,6 +6609,46 @@ void llvm::getUnderlyingObjects(const Value *V,
   } while (!Worklist.empty());
 }
 
+const Value *llvm::getUnderlyingObjectAggressive(const Value *V) {
+  const unsigned MaxVisited = 8;
+
+  SmallPtrSet<const Value *, 8> Visited;
+  SmallVector<const Value *, 8> Worklist;
+  Worklist.push_back(V);
+  const Value *Object = nullptr, *FirstObject = nullptr;
+  do {
+    const Value *P = Worklist.pop_back_val();
+    P = getUnderlyingObject(P);
+
+    if (!FirstObject)
+      FirstObject = P;
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fhahn wrote:

Should we pull this out of the loop if possible?

This would make it clear that we shouldn't end up in a situation where e.g. getUnderlyingObject returns nullptr for the initial pointer, and then we initialize FirstObject with the underlying object for one of the arms of a select and may end up returning an underlying object that just matches one side of the select.

https://github.com/llvm/llvm-project/pull/99509