Don't take the address of an xvalue when printing an expr result

Summary:
If we have an xvalue here, we will always hit the `err_typecheck_invalid_lvalue_addrof` error
in 'Sema::CheckAddressOfOperand' when trying to take the address of the result. This patch
uses the fallback code path where we store the result in a local variable instead when we hit
this case.

Fixes rdar://problem/40613277

Reviewers: jingham, vsk

Reviewed By: vsk

Subscribers: vsk, friss, lldb-commits

Differential Revision: https://reviews.llvm.org/D48303

llvm-svn: 336582

lldb/packages/Python/lldbsuite/test/expression_command/xvalue/Makefile

@@ -0,0 +1,5 @@
+LEVEL = ../../make
+
+CXX_SOURCES := main.cpp
+
+include $(LEVEL)/Makefile.rules

lldb/packages/Python/lldbsuite/test/expression_command/xvalue/TestXValuePrinting.py

@@ -0,0 +1,37 @@
+from __future__ import print_function
+
+
+import lldb
+from lldbsuite.test.decorators import *
+from lldbsuite.test.lldbtest import *
+from lldbsuite.test import lldbutil
+
+
+class ExprXValuePrintingTestCase(TestBase):
+
+    mydir = TestBase.compute_mydir(__file__)
+
+    def setUp(self):
+        # Call super's setUp().
+        TestBase.setUp(self)
+
+        self.main_source = "main.cpp"
+        self.main_source_spec = lldb.SBFileSpec(self.main_source)
+
+    def do_test(self, dictionary=None):
+        """Printing an xvalue should work."""
+        self.build(dictionary=dictionary)
+
+        (target, process, thread, bkpt) = lldbutil.run_to_source_breakpoint(self, 
+                                          '// Break here', self.main_source_spec)
+        frame = thread.GetFrameAtIndex(0)
+
+        value = frame.EvaluateExpression("foo().data")
+        self.assertTrue(value.IsValid())
+        self.assertTrue(value.GetError().Success())
+        self.assertEqual(value.GetValueAsSigned(), 1234)
+
+    @expectedFailureAll(oslist=["windows"], bugnumber="llvm.org/pr21765")
+    def test(self):
+        self.do_test()
+

lldb/packages/Python/lldbsuite/test/expression_command/xvalue/main.cpp

@@ -0,0 +1,12 @@
+struct Tmp
+{
+  int data = 1234;
+};
+
+Tmp foo() { return Tmp(); }
+
+int main(int argc, char const *argv[])
+{
+  int something = foo().data;
+  return 0; // Break here
+}

lldb/source/Plugins/ExpressionParser/Clang/ASTResultSynthesizer.cpp

@@ -292,9 +292,8 @@ bool ASTResultSynthesizer::SynthesizeBodyResult(CompoundStmt *Body,
   //
   //   - During dematerialization, $0 is ignored.
 
-  bool is_lvalue = (last_expr->getValueKind() == VK_LValue ||
-                    last_expr->getValueKind() == VK_XValue) &&
-                   (last_expr->getObjectKind() == OK_Ordinary);
+  bool is_lvalue = last_expr->getValueKind() == VK_LValue &&
+                   last_expr->getObjectKind() == OK_Ordinary;
 
   QualType expr_qual_type = last_expr->getType();
   const clang::Type *expr_type = expr_qual_type.getTypePtr();