Inspect global static const variables

[EwanCrawford]

Summary

This patch adds support for printing global static const variables which are given a DW_AT_const_value DWARF tag by clang.

Fix for bug https://llvm.org/bugs/show_bug.cgi?id=25653

[tberghammer]

LGTM (next time please upload the diff with full context)

lldb/trunk/packages/Python/lldbsuite/test/lang/c/global_variables/TestGlobalVariables.py

def test(self):
 
         # The breakpoint should have a hit count of 1.
         self.expect("breakpoint list -f", BREAKPOINT_HIT_ONCE,
             substrs = [' resolved, hit count = 1'])
 
         # Check that GLOBAL scopes are indicated for the variables.
         self.expect("frame variable --show-types --scope --show-globals --no-args", VARIABLES_DISPLAYED_CORRECTLY,
             substrs = ['GLOBAL: (int) g_file_global_int = 42',
+                       'STATIC: (const int) g_file_static_int = 2',
                        'GLOBAL: (const char *) g_file_global_cstr',
                        '"g_file_global_cstr"',
                        'STATIC: (const char *) g_file_static_cstr',
                        '"g_file_static_cstr"',
                        'GLOBAL: (int) g_common_1 = 21'])
 
         # 'frame variable' should support address-of operator.
         self.runCmd("frame variable &g_file_global_int")

lldb/trunk/packages/Python/lldbsuite/test/lang/c/global_variables/main.c

 //===-- main.c --------------------------------------------------*- C++ -*-===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 #include <stdio.h>
 
 int g_common_1; // Not initialized on purpose to cause it to be undefined external in .o file
 int g_file_global_int = 42;
+static const int g_file_static_int = 2;
 const char *g_file_global_cstr = "g_file_global_cstr";
 static const char *g_file_static_cstr = "g_file_static_cstr";
 
 extern int g_a;
 int main (int argc, char const *argv[])
 {
-    g_common_1 = g_file_global_int / 2;
+    g_common_1 = g_file_global_int / g_file_static_int;
     static const char *g_func_static_cstr = "g_func_static_cstr";
     printf ("%s %s\n", g_file_global_cstr, g_file_static_cstr);
     return g_file_global_int + g_a + g_common_1; // Set break point at this line.  //// break $source:$line; continue; var -global g_a -global g_global_int
 }

lldb/trunk/source/Core/ValueObject.cpp

ValueObject::GetData (DataExtractor& data, Error &error)
     UpdateValueIfNeeded(false);
     ExecutionContext exe_ctx (GetExecutionContextRef());
     error = m_value.GetValueAsData(&exe_ctx, data, 0, GetModule().get());
     if (error.Fail())
     {
         if (m_data.GetByteSize())
         {
             data = m_data;
+            error.Clear();
             return data.GetByteSize();
         }
         else
         {
             return 0;
         }
     }
     data.SetAddressByteSize(m_data.GetAddressByteSize());

lldb/trunk/source/Plugins/SymbolFile/DWARF/DWARFCompileUnit.cpp

for (pos = begin; pos != end; ++pos)
         }
 
         DWARFAttributes attributes;
         const char *name = NULL;
         const char *mangled_cstr = NULL;
         bool is_declaration = false;
         //bool is_artificial = false;
         bool has_address = false;
-        bool has_location = false;
+        bool has_location_or_const_value = false;
         bool is_global_or_static_variable = false;
         
         DWARFFormValue specification_die_form;
         const size_t num_attributes = die.GetAttributes(dwarf_cu, fixed_form_sizes, attributes);
         if (num_attributes > 0)
         {
             for (uint32_t i=0; i<num_attributes; ++i)
             {
//                    break;
                     has_address = true;
                     break;
 
                 case DW_AT_entry_pc:
                     has_address = true;
                     break;
 
                 case DW_AT_location:
-                    has_location = true;
+                case DW_AT_const_value:
+                    has_location_or_const_value = true;
                     if (tag == DW_TAG_variable)
                     {
                         const DWARFDebugInfoEntry* parent_die = die.GetParent();
                         while ( parent_die != NULL )
                         {
                             switch (parent_die->Tag())
                             {
                             case DW_TAG_subprogram:
//                              }
             break;
 
         case DW_TAG_namespace:
             if (name)
                 namespaces.Insert (ConstString(name), DIERef(cu_offset, die.GetOffset()));
             break;
 
         case DW_TAG_variable:
-            if (name && has_location && is_global_or_static_variable)
+            if (name && has_location_or_const_value && is_global_or_static_variable)
             {
                 globals.Insert (ConstString(name), DIERef(cu_offset, die.GetOffset()));
                 // Be sure to include variables by their mangled and demangled
                 // names if they have any since a variable can have a basename
                 // "i", a mangled named "_ZN12_GLOBAL__N_11iE" and a demangled 
                 // mangled name "(anonymous namespace)::i"...
                 
                 // Make sure our mangled name isn't the same string table entry

lldb/trunk/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp

if ((tag == DW_TAG_variable) ||
                                 // Variable didn't make it into the final executable
                                 return var_sp;
                             }
                         }
                     }
                 }
                 else
                 {
+                    if (location_is_const_value_data)
+                        scope = eValueTypeVariableStatic;
+                    else
                         scope = eValueTypeVariableLocal;
                 }
             }
 
             if (symbol_context_scope == NULL)
             {
                 switch (parent_tag)
                 {
                 case DW_TAG_subprogram: