New loplugin:classmemaccess

...to complement and improve upon GCC's -Wclass-memaccess.  See the comment at
the head of compilerplugins/clang/classmemaccess.cxx for details.  (It is not
yet clear to me whether we would want to get this upstreamed into Clang.)

35d21e4bf6f66b3bbc7a44fcf184cb721b524a94 "Remove redundant memsets" was a case
that benefited from looking through toplevel casts to void*.  (Though the code
in include/basic/sbxvar.hxx needs a slightly more verbose way to deliberately
silence the warning now.)

d03041e19215592f21ba1222d3cfa29e1f94260a "Drop bogus memsets" is one example of
various cases that GCC -Wclass-memaccess failed to catch due to the use of array
instead of pointer types.

Change-Id: I6a9bfc34e3536834af35fdf4fb7ceeb31f31f8c0
Reviewed-on: https://gerrit.libreoffice.org/80421
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>

1 files changed, 4 insertions, 3 deletions

diff --git a/include/basic/sbxvar.hxx b/include/basic/sbxvar.hxx
index 446f1fe4c1ec..270db0d137af 100644
--- a/include/basic/sbxvar.hxx
+++ b/include/basic/sbxvar.hxx
@@ -81,9 +81,10 @@ struct SbxValues
     void clear(SbxDataType type) {
         // A hacky way of zeroing the union value corresponding to the given type (even though the
         // relevant zero value need not be represented by all-zero bits, in general) without evoking
-        // GCC 8 -Wclass-memaccess, and without having to turn the anonymous union into a non-
-        // anonymous one:
-        std::memset(static_cast<void *>(this), 0, offsetof(SbxValues, eType));
+        // GCC 8 -Wclass-memaccess or loplugin:classmemaccess, and without having to turn the
+        // anonymous union into a non-anonymous one:
+        auto const p = static_cast<void *>(this);
+        std::memset(p, 0, offsetof(SbxValues, eType));
         eType = type;
     }
 };