Fix (and improve) the support for C99 variable length array types

Clang recently improved its DWARF support for C VLA types. The DWARF
now looks like this:

0x00000051:         DW_TAG_variable [4]
                     DW_AT_location( fbreg -32 )
                     DW_AT_name( "__vla_expr" )
                     DW_AT_type( {0x000000d3} ( long unsigned int ) )
                     DW_AT_artificial( true )
...
0x000000da:     DW_TAG_array_type [10] *
                 DW_AT_type( {0x000000cc} ( int ) )

0x000000df:         DW_TAG_subrange_type [11]
                     DW_AT_type( {0x000000e9} ( __ARRAY_SIZE_TYPE__ ) )
                     DW_AT_count( {0x00000051} )

Without this patch LLDB will naively interpret the DIE offset 0x51 as
the static size of the array, which is clearly wrong.  This patch
extends ValueObject::GetNumChildren to query the dynamic properties of
incomplete array types.

See the testcase for an example:

   4   int foo(int a) {
   5   	     int vla[a];
   6   	       for (int i = 0; i < a; ++i)
   7   	           vla[i] = i;
   8
-> 9            pause(); // break here
   10  		return vla[a-1];
   11   }

(lldb) fr v vla
(int []) vla = ([0] = 0, [1] = 1, [2] = 2, [3] = 3)
(lldb) quit

rdar://problem/21814005

Differential Revision: https://reviews.llvm.org/D53530

llvm-svn: 346165

1 files changed, 3 insertions, 1 deletions

diff --git a/lldb/source/Core/ValueObjectCast.cpp b/lldb/source/Core/ValueObjectCast.cpp
index f6ec026e079..da71141178a 100644
--- a/lldb/source/Core/ValueObjectCast.cpp
+++ b/lldb/source/Core/ValueObjectCast.cpp
@@ -44,7 +44,9 @@ ValueObjectCast::~ValueObjectCast() {}
 CompilerType ValueObjectCast::GetCompilerTypeImpl() { return m_cast_type; }
 
 size_t ValueObjectCast::CalculateNumChildren(uint32_t max) {
-  auto children_count = GetCompilerType().GetNumChildren(true);
+  ExecutionContext exe_ctx(GetExecutionContextRef());
+  auto children_count = GetCompilerType().GetNumChildren(
+      true, &exe_ctx);
   return children_count <= max ? children_count : max;
 }