SHA1: unroll loop in hashBlock.

SHA1: unroll loop in hashBlock.

This code is taken from public domain.
https://github.com/jsonn/src/blob/trunk/common/lib/libc/hash/sha1/sha1.c

I wrote a sha1 command and ran it on my Xeon E5-2680 v2 2.80GHz machine.
Here is a result. The new hash function is 37% faster than before.

 Performance counter stats for './llvm-sha1-old /ssd/build/bin/lld' (10 runs):

       6640.503687 task-clock (msec)         #    1.001 CPUs utilized            ( +-  0.03% )
                54 context-switches          #    0.008 K/sec                    ( +-  5.03% )
                 5 cpu-migrations            #    0.001 K/sec                    ( +- 31.73% )
           183,803 page-faults               #    0.028 M/sec                    ( +-  0.00% )
    18,527,954,113 cycles                    #    2.790 GHz                      ( +-  0.03% )
     4,993,237,485 stalled-cycles-frontend   #   26.95% frontend cycles idle     ( +-  0.11% )
   <not supported> stalled-cycles-backend
    50,217,149,423 instructions              #    2.71  insns per cycle
                                             #    0.10  stalled cycles per insn  ( +-  0.00% )
     6,094,322,337 branches                  #  917.750 M/sec                    ( +-  0.00% )
        11,778,239 branch-misses             #    0.19% of all branches          ( +-  0.01% )

       6.634017401 seconds time elapsed                                          ( +-  0.03% )

 Performance counter stats for './llvm-sha1-new /ssd/build/bin/lld' (10 runs):

       4167.062720 task-clock (msec)         #    1.001 CPUs utilized            ( +-  0.02% )
                52 context-switches          #    0.012 K/sec                    ( +- 16.45% )
                 7 cpu-migrations            #    0.002 K/sec                    ( +- 32.20% )
           183,804 page-faults               #    0.044 M/sec                    ( +-  0.00% )
    11,626,611,958 cycles                    #    2.790 GHz                      ( +-  0.02% )
     4,491,897,976 stalled-cycles-frontend   #   38.63% frontend cycles idle     ( +-  0.05% )
   <not supported> stalled-cycles-backend
    24,320,180,617 instructions              #    2.09  insns per cycle
                                             #    0.18  stalled cycles per insn  ( +-  0.00% )
     1,574,674,576 branches                  #  377.886 M/sec                    ( +-  0.00% )
        11,769,693 branch-misses             #    0.75% of all branches          ( +-  0.00% )

       4.163251552 seconds time elapsed                                          ( +-  0.02% )

Differential Revision: https://reviews.llvm.org/D26890

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@287473 91177308-0d34-0410-b5e6-96231b3b80d8