[lldb][NFC] Refactor test to enable subsequent reuse

[fdeazeve]

Summary

On a subsequent commit, I intend to update the expression and call the evaluate
function more times. This refactors enables reusing some of the existing code
for that.

[fdeazeve]

See the patch stack for the commit that benefits from this refactor.

lldb/unittests/Expression/DWARFExpressionTest.cpp

)";
   ASSERT_TRUE(debugger_sp);
   lldb::TargetSP target_sp;
   lldb::PlatformSP platform_sp;
   debugger_sp->GetTargetList().CreateTarget(*debugger_sp, "", arch,
                                             lldb_private::eLoadDependentsNo,
                                             platform_sp, target_sp);
 
   ExecutionContext exe_ctx(target_sp, false);
-  // DW_OP_addrx takes a single leb128 operand, the index in the addr table:
-  uint8_t expr[] = {DW_OP_addrx, 0x01};
-  DataExtractor extractor(expr, sizeof(expr), lldb::eByteOrderLittle,
-                          /*addr_size*/ 4);
-  Value result;
-  Status status;
-  ASSERT_TRUE(DWARFExpression::Evaluate(
+
+  auto evaluate = [&](DWARFExpression &expr, Status &status, Value &result) {
+    DataExtractor extractor;
+    expr.GetExpressionData(extractor);
+    return DWARFExpression::Evaluate(
         &exe_ctx, /*reg_ctx*/ nullptr, /*module_sp*/ {}, extractor, dwarf_cu,
         lldb::eRegisterKindLLDB,
         /*initial_value_ptr*/ nullptr,
-      /*object_address_ptr*/ nullptr, result, &status))
-      << status.ToError();
+        /*object_address_ptr*/ nullptr, result, &status);
+  };
 
+  // DW_OP_addrx takes a single leb128 operand, the index in the addr table:
+  uint8_t expr_data[] = {DW_OP_addrx, 0x01};
+  DataExtractor extractor(expr_data, sizeof(expr_data), lldb::eByteOrderLittle,
+                          /*addr_size*/ 4);
+  DWARFExpression expr(extractor);
+
+  Status status;
+  Value result;
+  ASSERT_TRUE(evaluate(expr, status, result)) << status.ToError();
   ASSERT_EQ(result.GetValueType(), Value::ValueType::LoadAddress);
   ASSERT_EQ(result.GetScalar().UInt(), 0x5678u);
 }
 
 class CustomSymbolFileDWARF : public SymbolFileDWARF {
   static char ID;
 
 public: