[Bug libstdc++/57885] unordered_map find slower in 4.8.1 than 4.7.3 with integer key

["jhand at austin dot rr.com" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57885

--- Comment #4 from Jim Hand <jhand at austin dot rr.com> ---
I compiled 4.9.0-20130714 today and ran the same tests. Here are the results
for the lookup loops with the times for each compiler:

4.6.3: 11536 microseconds
4.7.3: 12150 microseconds  (5.3% slower than 4.6.3)
4.8.2: 14810 microseconds  (28.3% slower than 4.6.3)
4.9.0-20130714 15365 microseconds (33.1% slower than 4.6.3)

I took a look at the assembly for the "return a.find(5) != a.end();" code for
4.9 and it looks very similar to the 4.8 assembly, but contains two extra
instructions at the beginning of the function:

    testq    %r8, %r8
     je    .L8

I guess those two instructions explain the the slightly worse behavior for
4.9.0 than 4.8.2.