[Bug sanitizer/55309] gcc's address-sanitizer 66% slower than clang's

[kcc at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55309



--- Comment #30 from Kostya Serebryany <kcc at gcc dot gnu.org> 2013-02-11 
14:42:43 UTC ---

> Could we on x86_64 think about mem_to_shadow(x) (x >> 3) + 0x7fff8000



Committed http://llvm.org/viewvc/llvm-project?rev=174886&view=rev

which adds an optional flag -mllvm -asan-short-64bit-mapping-offset=1



On bzip2/train it gives us ~ 2/3 of the zero-base-offset benefits:

                  orig          0x7fff8000    zero      

401.bzip2,        68.80,        64.80,        62.70



Measuring the rest. 



Note that with clang this did not require any change in the run-time

(since recently we switched to ASAN_FLEXIBLE_MAPPING_AND_OFFSET=1)