[Bug sanitizer/55975] asan does not work with 46 bit address space on PowerPC64

["jakub at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55975

--- Comment #26 from Jakub Jelinek <jakub at gcc dot gnu.org> 2013-01-23 12:26:30 UTC ---
(In reply to comment #25)
> So, what is our decision? 
> 
> Are we just doing 
> -  static const uptr kHighMemEnd = 0x00000fffffffffffUL;
> +  static const uptr kHighMemEnd = 0x00003fffffffffffUL;
> , leaving SHADOW_OFFSET=(1ULL << 41)
> and using ADD instead of OR when applying SHADOW_OFFSET? 
> 
> This seems to work on my ppc box (44-bit) with LLVM
> (I've changed it to use ADD on PPC)

If that works, it is my preference.  But needs testing, also with GCC, and with
both 44-bit and 46-bit AS.

BTW, I wonder why clang generates larger and slower code with ADD instead of
OR, at least gcc seems to generate generally better code with ADD, plus on
i?86/x86_64 it even has better HW support for that (for ADD can use both
add{l,q} and leal, allowing RA to generate better code).  GCC for asan
generates always ADD, on all architectures, right now.