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

3 files changed, 45 insertions, 0 deletions

diff --git a/lldb/packages/Python/lldbsuite/test/lang/c/vla/Makefile b/lldb/packages/Python/lldbsuite/test/lang/c/vla/Makefile
new file mode 100644
index 00000000000..b09a579159d
--- /dev/null
+++ b/lldb/packages/Python/lldbsuite/test/lang/c/vla/Makefile
@@ -0,0 +1,5 @@
+LEVEL = ../../../make
+
+C_SOURCES := main.c
+
+include $(LEVEL)/Makefile.rules
diff --git a/lldb/packages/Python/lldbsuite/test/lang/c/vla/TestVLA.py b/lldb/packages/Python/lldbsuite/test/lang/c/vla/TestVLA.py
new file mode 100644
index 00000000000..0d3a0a69a50
--- /dev/null
+++ b/lldb/packages/Python/lldbsuite/test/lang/c/vla/TestVLA.py
@@ -0,0 +1,25 @@
+import lldb
+from lldbsuite.test.lldbtest import *
+import lldbsuite.test.lldbutil as lldbutil
+
+
+class TestVLA(TestBase):
+
+    mydir = TestBase.compute_mydir(__file__)
+
+    def test_vla(self):
+        self.build()
+        _, process, _, _ = lldbutil.run_to_source_breakpoint(
+            self, "break here", lldb.SBFileSpec('main.c'))
+
+        def test(a, array):
+            for i in range(a):
+                self.expect("fr v vla[%d]"%i, substrs=["int", "%d"%(a-i)])
+                self.expect("expr vla[%d]"%i, substrs=["int", "%d"%(a-i)])
+            self.expect("frame var vla", substrs=array)
+            self.expect("expr      vla", error=True, substrs=["incomplete"])
+
+        test(2, ["int []", "[0] = 2, [1] = 1"])
+        process.Continue()
+        test(4, ["int []", "[0] = 4, [1] = 3, [2] = 2, [3] = 1"])
+
diff --git a/lldb/packages/Python/lldbsuite/test/lang/c/vla/main.c b/lldb/packages/Python/lldbsuite/test/lang/c/vla/main.c
new file mode 100644
index 00000000000..ba9cc185560
--- /dev/null
+++ b/lldb/packages/Python/lldbsuite/test/lang/c/vla/main.c
@@ -0,0 +1,15 @@
+void pause() {}
+
+int foo(int a) {
+  int vla[a];
+
+  for (int i = 0; i < a; ++i)
+    vla[i] = a-i;
+
+  pause(); // break here
+  return vla[a-1];
+}
+
+int main (void) {
+  return foo(2) + foo(4);
+}