[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, 46 insertions, 0 deletions

diff --git a/lldb/packages/Python/lldbsuite/test/expression_command/context-object/main.cpp b/lldb/packages/Python/lldbsuite/test/expression_command/context-object/main.cpp
new file mode 100644
index 00000000000..098b6089fce
--- /dev/null
+++ b/lldb/packages/Python/lldbsuite/test/expression_command/context-object/main.cpp
@@ -0,0 +1,46 @@
+namespace cpp_namespace {
+  struct CppStruct {
+    int field = 1111;
+
+    int function() {
+      return 2222;
+    }
+  };
+
+  union CppUnion {
+    char field_char;
+    short field_short;
+    int field_int;
+  };
+
+  CppStruct GetCppStruct() {
+    return CppStruct();
+  }
+
+  CppStruct global;
+
+  CppStruct *GetCppStructPtr() {
+    return &global;
+  }
+}
+
+int global = 3333;
+
+int main()
+{
+  cpp_namespace::CppStruct cpp_struct = cpp_namespace::GetCppStruct();
+  cpp_struct.function();
+
+  int field = 4444;
+
+  cpp_namespace::CppUnion cpp_union;
+  cpp_union.field_int = 5555;
+
+  int cpp_scalar = 6666;
+
+  cpp_namespace::CppStruct cpp_array[16];
+
+  cpp_namespace::CppStruct *cpp_pointer = cpp_namespace::GetCppStructPtr();
+
+  return 0; // Break here
+}