[Attributor]: allow more than one offset for a pass through user in AAPointerInfo (#94416)

Co-authored-by: Vidush Singhal <[email protected]>

Author: vidsinghal

llvm/lib/Transforms/IPO/AttributorAttributes.cpp

@@ -1608,11 +1608,15 @@ ChangeStatus AAPointerInfoFloating::updateImpl(Attributor &A) {
     //
     // The RHS is a reference that may be invalidated by an insertion caused by
     // the LHS. So we ensure that the side-effect of the LHS happens first.
+
+    assert(OffsetInfoMap.contains(CurPtr) &&
+           "CurPtr does not exist in the map!");
+
     auto &UsrOI = OffsetInfoMap[Usr];
     auto &PtrOI = OffsetInfoMap[CurPtr];
     assert(!PtrOI.isUnassigned() &&
            "Cannot pass through if the input Ptr was not visited!");
-    UsrOI = PtrOI;
+    UsrOI.merge(PtrOI);
     Follow = true;
     return true;
   };