[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, 47 insertions, 0 deletions

diff --git a/lldb/packages/Python/lldbsuite/test/expression_command/context-object-objc/main.m b/lldb/packages/Python/lldbsuite/test/expression_command/context-object-objc/main.m
new file mode 100644
index 00000000000..5c495b24894
--- /dev/null
+++ b/lldb/packages/Python/lldbsuite/test/expression_command/context-object-objc/main.m
@@ -0,0 +1,47 @@
+#import <Foundation/Foundation.h>
+
+@interface ObjcClass : NSObject {
+    int field;
+}
+
+@property int property;
+
++(ObjcClass*)createNew;
+
+-(id)init;
+
+-(int)method;
+
+@end
+
+@implementation ObjcClass
+
++(ObjcClass*)createNew {
+    return [ObjcClass new];
+}
+
+-(id)init {
+    self = [super init];
+    if (self) {
+        field = 1111;
+        _property = 2222;
+    }
+    return self;
+}
+
+-(int)method {
+    return 3333;
+}
+
+@end
+
+int main()
+{
+    @autoreleasepool {
+        ObjcClass* objcClass = [ObjcClass new];
+        
+        int field = 4444;
+        
+        return 0; // Break here
+    }
+}