[lldb] Fix updating persistent variables without JIT (llvm#149642)

This patch fixes updating persistent variables when memory cannot be
allocated in an inferior process:
```
> lldb -c test.core
(lldb) expr int $i = 5
(lldb) expr $i = 55
(int) $0 = 55
(lldb) expr $i
(int) $i = 5
```

With this patch, the last command prints:
```
(int) $i = 55
```

The issue was introduced in llvm#145599.

Author: igorkudrin

lldb/source/Expression/Materializer.cpp

@@ -102,22 +102,23 @@ class EntityPersistentVariable : public Materializer::Entity {
         m_persistent_variable_sp->GetName(), mem, eAddressTypeLoad,
         map.GetAddressByteSize());
 
-    if (m_persistent_variable_sp->m_flags &
-        ExpressionVariable::EVKeepInTarget) {
-      if (used_policy == IRMemoryMap::eAllocationPolicyMirror) {
+    if (used_policy == IRMemoryMap::eAllocationPolicyMirror) {
+      if (m_persistent_variable_sp->m_flags &
+          ExpressionVariable::EVKeepInTarget) {
         // Clear the flag if the variable will never be deallocated.
         Status leak_error;
         map.Leak(mem, leak_error);
         m_persistent_variable_sp->m_flags &=
             ~ExpressionVariable::EVNeedsAllocation;
-      } else {
-        // If the variable cannot be kept in target, clear this flag...
-        m_persistent_variable_sp->m_flags &=
-            ~ExpressionVariable::EVKeepInTarget;
-        // ...and set the flag to copy the value during dematerialization.
-        m_persistent_variable_sp->m_flags |=
-            ExpressionVariable::EVNeedsFreezeDry;
       }
+    } else {
+      // If we cannot allocate memory in the process,
+      // - clear the 'EVKeepInTarget' flag to ensure that 'm_live_sp' is reset
+      //   during dematerialization,
+      m_persistent_variable_sp->m_flags &= ~ExpressionVariable::EVKeepInTarget;
+      // - set the 'EVNeedsFreezeDry' flag so that the value is copied to
+      //   'm_frozen_sp' during dematerialization.
+      m_persistent_variable_sp->m_flags |= ExpressionVariable::EVNeedsFreezeDry;
     }
 
     // Write the contents of the variable to the area.

lldb/test/API/functionalities/postmortem/elf-core/expr/TestExpr.py

@@ -37,6 +37,10 @@ def test_persist_var(self):
         self.target.EvaluateExpression("int $my_int = 5")
         self.expect_expr("$my_int * 2", result_type="int", result_value="10")
 
+        # Try assigning the persistent variable a new value.
+        self.target.EvaluateExpression("$my_int = 55")
+        self.expect_expr("$my_int", result_type="int", result_value="55")
+
     def test_context_object(self):
         """Test expression evaluation in context of an object."""