Index: lldb/include/lldb/Symbol/ClangASTImporter.h
===================================================================
--- lldb/include/lldb/Symbol/ClangASTImporter.h
+++ lldb/include/lldb/Symbol/ClangASTImporter.h
@@ -67,7 +67,7 @@
       llvm::DenseMap<const clang::CXXRecordDecl *, clang::CharUnits>
           &base_offsets,
       llvm::DenseMap<const clang::CXXRecordDecl *, clang::CharUnits>
-          &vbase_offsets);
+          &vbase_offsets) const;
 
   bool CanImport(const CompilerType &type);
 
Index: lldb/source/Symbol/ClangASTImporter.cpp
===================================================================
--- lldb/source/Symbol/ClangASTImporter.cpp
+++ lldb/source/Symbol/ClangASTImporter.cpp
@@ -525,26 +525,23 @@
     llvm::DenseMap<const clang::CXXRecordDecl *, clang::CharUnits>
         &base_offsets,
     llvm::DenseMap<const clang::CXXRecordDecl *, clang::CharUnits>
-        &vbase_offsets) {
-  RecordDeclToLayoutMap::iterator pos =
+        &vbase_offsets) const {
+  RecordDeclToLayoutMap::const_iterator pos =
       m_record_decl_to_layout_map.find(record_decl);
-  bool success = false;
   base_offsets.clear();
   vbase_offsets.clear();
   if (pos != m_record_decl_to_layout_map.end()) {
     bit_size = pos->second.bit_size;
     alignment = pos->second.alignment;
-    field_offsets.swap(pos->second.field_offsets);
-    base_offsets.swap(pos->second.base_offsets);
-    vbase_offsets.swap(pos->second.vbase_offsets);
-    m_record_decl_to_layout_map.erase(pos);
-    success = true;
-  } else {
-    bit_size = 0;
-    alignment = 0;
-    field_offsets.clear();
+    field_offsets = pos->second.field_offsets;
+    base_offsets = pos->second.base_offsets;
+    vbase_offsets = pos->second.vbase_offsets;
+    return true;
   }
-  return success;
+  bit_size = 0;
+  alignment = 0;
+  field_offsets.clear();
+  return false;
 }
 
 void ClangASTImporter::InsertRecordDecl(clang::RecordDecl *decl,
Index: lldb/unittests/Symbol/TestClangASTImporter.cpp
===================================================================
--- lldb/unittests/Symbol/TestClangASTImporter.cpp
+++ lldb/unittests/Symbol/TestClangASTImporter.cpp
@@ -203,18 +203,25 @@
   layout_info.field_offsets[field] = 1;
   importer.InsertRecordDecl(source_record, layout_info);
 
-  uint64_t bit_size;
-  uint64_t alignment;
-  llvm::DenseMap<const clang::FieldDecl *, uint64_t> field_offsets;
-  llvm::DenseMap<const clang::CXXRecordDecl *, clang::CharUnits> base_offsets;
-  llvm::DenseMap<const clang::CXXRecordDecl *, clang::CharUnits> vbase_offsets;
-  importer.LayoutRecordType(source_record, bit_size, alignment, field_offsets,
-                            base_offsets, vbase_offsets);
-
-  EXPECT_EQ(15U, bit_size);
-  EXPECT_EQ(2U, alignment);
-  EXPECT_EQ(1U, field_offsets.size());
-  EXPECT_EQ(1U, field_offsets[field]);
-  EXPECT_EQ(0U, base_offsets.size());
-  EXPECT_EQ(0U, vbase_offsets.size());
+  // Check that asking for the layout multiple times will always return the
+  // same result. Three times should be enough to find any changing
+  for (unsigned i = 0; i < 3U; ++i) {
+    SCOPED_TRACE("Iteration: " + std::to_string(i));
+
+    uint64_t bit_size;
+    uint64_t alignment;
+    llvm::DenseMap<const clang::FieldDecl *, uint64_t> field_offsets;
+    llvm::DenseMap<const clang::CXXRecordDecl *, clang::CharUnits> base_offsets;
+    llvm::DenseMap<const clang::CXXRecordDecl *, clang::CharUnits>
+        vbase_offsets;
+    importer.LayoutRecordType(source_record, bit_size, alignment, field_offsets,
+                              base_offsets, vbase_offsets);
+
+    EXPECT_EQ(15U, bit_size);
+    EXPECT_EQ(2U, alignment);
+    EXPECT_EQ(1U, field_offsets.size());
+    EXPECT_EQ(1U, field_offsets[field]);
+    EXPECT_EQ(0U, base_offsets.size());
+    EXPECT_EQ(0U, vbase_offsets.size());
+  }
 }