[lldb] Avoid returning a stale AddressOf (#212915)

The 'ValueObject::AddressOf()' method assumes that the address of a
value object cannot change, so when it is calculated once, it does not
need to be updated afterwards. However, this is not the case if the
'ValueObject' is a dependent object obtained by calling 'Dereference()'
of another 'ValueObject'. If the latter object is changed, the dependent
value object should return a new address from the 'AddressOf()' method
to reflect the change.

lldb/source/ValueObject/ValueObject.cpp

@@ -2913,9 +2913,6 @@ ValueObjectSP ValueObject::Dereference(Status &error) {
 }
 
 ValueObjectSP ValueObject::AddressOf(Status &error) {
-  if (m_addr_of_valobj_sp)
-    return m_addr_of_valobj_sp;
-
   auto [addr, address_type] = GetAddressOf(/*scalar_is_load_address=*/false);
   error.Clear();
   if (addr != LLDB_INVALID_ADDRESS && address_type != eAddressTypeHost) {
@@ -2929,6 +2926,10 @@ ValueObjectSP ValueObject::AddressOf(Status &error) {
 
     case eAddressTypeFile:
     case eAddressTypeLoad: {
+      if (m_addr_of_valobj_sp &&
+          m_addr_of_valobj_sp->GetValueAsUnsigned(LLDB_INVALID_ADDRESS) == addr)
+        return m_addr_of_valobj_sp;
+      m_addr_of_valobj_sp.reset();
       CompilerType compiler_type = GetCompilerType();
       if (compiler_type) {
         std::string name(1, '&');

lldb/test/API/python_api/value/change_ptr/Makefile

@@ -0,0 +1,3 @@
+C_SOURCES := main.c
+
+include Makefile.rules

lldb/test/API/python_api/value/change_ptr/TestChangePtr.py

@@ -0,0 +1,65 @@
+import lldb
+from lldbsuite.test.decorators import *
+from lldbsuite.test.lldbtest import *
+from lldbsuite.test import lldbutil
+
+
+class ChangePtrTest(TestBase):
+    def test(self):
+        self.build()
+
+        src_file = lldb.SBFileSpec("main.c")
+        _, process, thread, _ = lldbutil.run_to_source_breakpoint(
+            self, "// break here 1", src_file
+        )
+
+        ## Test 1: The AddressOf of a dereferenced value should change when
+        ## the pointer value is updated.
+
+        frame = thread.GetFrameAtIndex(0)
+        p = frame.FindVariable("p")
+        deref = p.Dereference()
+        self.assertEqual(deref.GetValueAsUnsigned(), 5)
+        self.assertEqual(deref.AddressOf().GetValueAsUnsigned(), p.GetValueAsUnsigned())
+        thread.StepOver()
+        self.assertEqual(deref.GetValueAsUnsigned(), 7)
+        self.assertEqual(deref.AddressOf().GetValueAsUnsigned(), p.GetValueAsUnsigned())
+
+        ## Test 2: The AddressOf of a child value of a dereferenced value should
+        ## change when the base pointer updates.
+
+        lldbutil.continue_to_source_breakpoint(
+            self, process, "// break here 2", src_file
+        )
+        frame = thread.GetFrameAtIndex(0)
+        p = frame.FindVariable("p")
+        deref_child = p.Dereference().GetChildMemberWithName("b")
+        self.assertEqual(deref_child.GetValue(), "'b'")
+        self.assertEqual(
+            deref_child.AddressOf().GetValueAsUnsigned(), p.GetValueAsUnsigned() + 1
+        )
+        thread.StepOver()
+        self.assertEqual(deref_child.GetValue(), "'d'")
+        self.assertEqual(
+            deref_child.AddressOf().GetValueAsUnsigned(), p.GetValueAsUnsigned() + 1
+        )
+
+        ## Test 3: Verify AddressOf updates correctly with persistent expression results.
+        lldbutil.continue_to_source_breakpoint(
+            self, process, "// break here 3", src_file
+        )
+        frame = thread.GetFrameAtIndex(0)
+        frame.EvaluateExpression("int *$ptr = &a")
+        ptr = frame.FindValue("$ptr", lldb.eValueTypeConstResult)
+        deref = ptr.Dereference()
+        self.assertEqual(deref.GetValueAsUnsigned(), 5)
+        self.assertEqual(
+            deref.AddressOf().GetValueAsUnsigned(),
+            frame.FindVariable("a").AddressOf().GetValueAsUnsigned(),
+        )
+        frame.EvaluateExpression("$ptr = &b")
+        self.assertEqual(deref.GetValueAsUnsigned(), 7)
+        self.assertEqual(
+            deref.AddressOf().GetValueAsUnsigned(),
+            frame.FindVariable("b").AddressOf().GetValueAsUnsigned(),
+        )

lldb/test/API/python_api/value/change_ptr/main.c

@@ -0,0 +1,31 @@
+int test1() {
+  int a = 5;
+  int b = 7;
+  int *p = &a;
+  p = &b; // break here 1
+  return *p;
+}
+
+char test2() {
+  struct S {
+    char a;
+    char b;
+  };
+  struct S arr[2] = {{'a', 'b'}, {'c', 'd'}};
+  struct S *p = arr;
+  ++p; // break here 2
+  return p->b;
+}
+
+int test3() {
+  int a = 5;
+  int b = 7;
+  return a + b; // break here 3
+}
+
+int main() {
+  test1();
+  test2();
+  test3();
+  return 0;
+}