[ubsan] Have -fsanitize=vptr emit a null check if -fsanitize=null isn't available

In r309007, I made -fsanitize=null a hard prerequisite for -fsanitize=vptr. I
did not see the need for the two checks to have separate null checking logic
for the same pointer. I expected the two checks to either always be enabled
together, or to be mutually compatible.

In the mailing list discussion re: r309007 it became clear that that isn't the
case. If a codebase is -fsanitize=vptr clean but not -fsanitize=null clean,
it's useful to have -fsanitize=vptr emit its own null check. That's what this
patch does: with it, -fsanitize=vptr can be used without -fsanitize=null.

Differential Revision: https://reviews.llvm.org/D36112

llvm-svn: 309846

1 files changed, 4 insertions, 4 deletions

diff --git a/clang/docs/UndefinedBehaviorSanitizer.rst b/clang/docs/UndefinedBehaviorSanitizer.rst
index 6274054..aa52f2d 100644
--- a/clang/docs/UndefinedBehaviorSanitizer.rst
+++ b/clang/docs/UndefinedBehaviorSanitizer.rst
@@ -132,10 +132,10 @@ Available checks are:
   -  ``-fsanitize=vla-bound``: A variable-length array whose bound
      does not evaluate to a positive value.
   -  ``-fsanitize=vptr``: Use of an object whose vptr indicates that it is of
-     the wrong dynamic type, or that its lifetime has not begun or has ended.
-     Incompatible with ``-fno-rtti`` and ``-fno-sanitize=null``. Link must be
-     performed by ``clang++``, not ``clang``, to make sure C++-specific parts of
-     the runtime library and C++ standard libraries are present.
+    the wrong dynamic type, or that its lifetime has not begun or has ended.
+    Incompatible with ``-fno-rtti``. Link must be performed by ``clang++``, not
+    ``clang``, to make sure C++-specific parts of the runtime library and C++
+    standard libraries are present.
 
 You can also use the following check groups:
   -  ``-fsanitize=undefined``: All of the checks listed above other than