[Bug sanitizer/67513] ASAN: Not optimal shadow value check (unlikely condition checked in fast path)

[y.gribov at samsung dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67513

--- Comment #1 from Yury Gribov <y.gribov at samsung dot com> ---
(In reply to Andrey Ryabinin from comment #0)
> (shadow value is usually zero).

What makes you think so? AFAIU for less-than-8-byte scalars it's always
non-zero. I vaguely remember than Kostya did something like this in Clang case
and it resulted in negligeable improvement.