[Attributor][FIX] Ensure we do not use stale references (#104495)

When copying map entries, we might run into resizing and invalidate the
RHS of the assignment. We dealt with this before and now use the proper
helper to avoid the problem in another place.

Fixes: #104397

Author: jdoerfert

llvm/lib/Transforms/IPO/AttributorAttributes.cpp

@@ -1628,6 +1628,8 @@ ChangeStatus AAPointerInfoFloating::updateImpl(Attributor &A) {
                       << "\n");
     assert(OffsetInfoMap.count(CurPtr) &&
            "The current pointer offset should have been seeded!");
+    assert(!OffsetInfoMap[CurPtr].isUnassigned() &&
+           "Current pointer should be assigned");
 
     if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Usr)) {
       if (CE->isCast())
@@ -1906,6 +1908,7 @@ ChangeStatus AAPointerInfoFloating::updateImpl(Attributor &A) {
   };
   auto EquivalentUseCB = [&](const Use &OldU, const Use &NewU) {
     assert(OffsetInfoMap.count(OldU) && "Old use should be known already!");
+    assert(!OffsetInfoMap[OldU].isUnassigned() && "Old use should be assinged");
     if (OffsetInfoMap.count(NewU)) {
       LLVM_DEBUG({
         if (!(OffsetInfoMap[NewU] == OffsetInfoMap[OldU])) {
@@ -1916,8 +1919,8 @@ ChangeStatus AAPointerInfoFloating::updateImpl(Attributor &A) {
       });
       return OffsetInfoMap[NewU] == OffsetInfoMap[OldU];
     }
-    OffsetInfoMap[NewU] = OffsetInfoMap[OldU];
-    return true;
+    bool Unused;
+    return HandlePassthroughUser(NewU.get(), OldU.get(), Unused);
   };
   if (!A.checkForAllUses(UsePred, *this, AssociatedValue,
                          /* CheckBBLivenessOnly */ true, DepClassTy::OPTIONAL,