ArrayBoundCheckerV2: don't arbitrarily warn about indexing before the 0-index of a symbolic region.  In many cases that isn't really the base offset.

llvm-svn: 129366
diff --git a/clang/test/Analysis/out-of-bounds.c b/clang/test/Analysis/out-of-bounds.c
index d6eca06..8c65b47 100644
--- a/clang/test/Analysis/out-of-bounds.c
+++ b/clang/test/Analysis/out-of-bounds.c
@@ -146,3 +146,12 @@
   if (x > 99)
     buf[x] = 1; 
 }
+
+// Don't warn when indexing below the start of a symbolic region's whose
+// base extent we don't know.
+int *get_symbolic();
+void test_index_below_symboloc() {
+  int *buf = get_symbolic();
+  buf[-1] = 0; // no-warning;
+}
+