[Expressions] Add support of expressions evaluation in some object's context

Summary:
This patch adds support of expression evaluation in a context of some object.
Consider the following example:
```
struct S {
  int a = 11;
  int b = 12;
};

int main() {
  S s;
  int a = 1;
  int b = 2;
  // We have stopped here
  return 0;
}
```
This patch allows to do something like that:
```
lldb.frame.FindVariable("s").EvaluateExpression("a + b")
```
and the result will be `33` (not `3`) because fields `a` and `b` of `s` will be
used (not locals `a` and `b`).

This is achieved by replacing of `this` type and object for the expression. This
has some limitations: an expression can be evaluated only for values located in
the debuggee process memory (they must have an address of `eAddressTypeLoad`
type).

Reviewers: teemperor, clayborg, jingham, zturner, labath, davide, spyffe, serge-sans-paille

Reviewed By: jingham

Subscribers: abidh, lldb-commits, leonid.mashinskiy

Tags: #lldb

Differential Revision: https://reviews.llvm.org/D55318

llvm-svn: 353149

1 files changed, 36 insertions, 4 deletions

diff --git a/lldb/source/Plugins/ExpressionParser/Clang/ClangExpressionDeclMap.cpp b/lldb/source/Plugins/ExpressionParser/Clang/ClangExpressionDeclMap.cpp
index 745341b2d04..6e7f11fed5f 100644
--- a/lldb/source/Plugins/ExpressionParser/Clang/ClangExpressionDeclMap.cpp
+++ b/lldb/source/Plugins/ExpressionParser/Clang/ClangExpressionDeclMap.cpp
@@ -65,10 +65,12 @@ const char *g_lldb_local_vars_namespace_cstr = "$__lldb_local_vars";
 ClangExpressionDeclMap::ClangExpressionDeclMap(
     bool keep_result_in_memory,
     Materializer::PersistentVariableDelegate *result_delegate,
-    ExecutionContext &exe_ctx)
+    ExecutionContext &exe_ctx,
+    ValueObject *ctx_obj)
     : ClangASTSource(exe_ctx.GetTargetSP()), m_found_entities(),
       m_struct_members(), m_keep_result_in_memory(keep_result_in_memory),
-      m_result_delegate(result_delegate), m_parser_vars(), m_struct_vars() {
+      m_result_delegate(result_delegate), m_parser_vars(), m_struct_vars(),
+      m_ctx_obj(ctx_obj) {
   EnableStructVars();
 }
 
@@ -927,6 +929,21 @@ void ClangExpressionDeclMap::FindExternalVisibleDecls(
     static ConstString g_lldb_class_name("$__lldb_class");
 
     if (name == g_lldb_class_name) {
+      if (m_ctx_obj) {
+        Status status;
+        lldb::ValueObjectSP ctx_obj_ptr = m_ctx_obj->AddressOf(status);
+        if (!ctx_obj_ptr || status.Fail())
+          return;
+
+        AddThisType(context, TypeFromUser(m_ctx_obj->GetCompilerType()),
+                    current_id);
+
+        m_struct_vars->m_object_pointer_type =
+            TypeFromUser(ctx_obj_ptr->GetCompilerType());
+
+        return;
+      }
+
       // Clang is looking for the type of "this"
 
       if (frame == NULL)
@@ -1019,6 +1036,21 @@ void ClangExpressionDeclMap::FindExternalVisibleDecls(
 
     static ConstString g_lldb_objc_class_name("$__lldb_objc_class");
     if (name == g_lldb_objc_class_name) {
+      if (m_ctx_obj) {
+        Status status;
+        lldb::ValueObjectSP ctx_obj_ptr = m_ctx_obj->AddressOf(status);
+        if (!ctx_obj_ptr || status.Fail())
+          return;
+
+        AddOneType(context, TypeFromUser(m_ctx_obj->GetCompilerType()),
+                    current_id);
+
+        m_struct_vars->m_object_pointer_type =
+            TypeFromUser(ctx_obj_ptr->GetCompilerType());
+
+        return;
+      }
+
       // Clang is looking for the type of "*self"
 
       if (!frame)
@@ -2124,7 +2156,7 @@ void ClangExpressionDeclMap::AddOneFunction(NameSearchContext &context,
 }
 
 void ClangExpressionDeclMap::AddThisType(NameSearchContext &context,
-                                         TypeFromUser &ut,
+                                         const TypeFromUser &ut,
                                          unsigned int current_id) {
   CompilerType copied_clang_type = GuardedCopyType(ut);
 
@@ -2198,7 +2230,7 @@ void ClangExpressionDeclMap::AddThisType(NameSearchContext &context,
 }
 
 void ClangExpressionDeclMap::AddOneType(NameSearchContext &context,
-                                        TypeFromUser &ut,
+                                        const TypeFromUser &ut,
                                         unsigned int current_id) {
   CompilerType copied_clang_type = GuardedCopyType(ut);