Add suport of read-modify-write for AND/SUB/AND/OR/XOR on amd64.

1. The total size of pkg/linux_amd64 decreases about 4KB, excluding
cmd/compile.

2. The go1 benchmark shows a little improvement, excluding noise.

name                     old time/op    new time/op    delta
BinaryTree17-4              2.63s ± 3%     2.65s ± 4%   +1.01%  (p=0.037 n=35+35)
Fannkuch11-4                2.33s ± 2%     2.39s ± 2%   +2.49%  (p=0.000 n=35+35)
FmtFprintfEmpty-4          45.4ns ± 5%    40.8ns ± 6%  -10.09%  (p=0.000 n=35+35)
FmtFprintfString-4         73.3ns ± 4%    70.9ns ± 3%   -3.23%  (p=0.000 n=30+35)
FmtFprintfInt-4            79.9ns ± 4%    79.5ns ± 3%     ~     (p=0.736 n=34+35)
FmtFprintfIntInt-4          126ns ± 4%     125ns ± 4%     ~     (p=0.083 n=35+35)
FmtFprintfPrefixedInt-4     152ns ± 6%     152ns ± 3%     ~     (p=0.855 n=34+35)
FmtFprintfFloat-4           215ns ± 4%     213ns ± 4%     ~     (p=0.066 n=35+35)
FmtManyArgs-4               522ns ± 3%     506ns ± 3%   -3.15%  (p=0.000 n=35+35)
GobDecode-4                6.45ms ± 8%    6.51ms ± 7%   +0.96%  (p=0.026 n=35+35)
GobEncode-4                6.10ms ± 6%    6.02ms ± 8%     ~     (p=0.160 n=35+35)
Gzip-4                      228ms ± 3%     221ms ± 3%   -2.92%  (p=0.000 n=35+35)
Gunzip-4                   37.5ms ± 4%    37.2ms ± 3%   -0.78%  (p=0.036 n=35+35)
HTTPClientServer-4         58.7µs ± 2%    59.2µs ± 1%   +0.80%  (p=0.000 n=33+33)
JSONEncode-4               12.0ms ± 3%    12.2ms ± 3%   +1.84%  (p=0.008 n=35+35)
JSONDecode-4               57.0ms ± 4%    56.6ms ± 3%     ~     (p=0.320 n=35+35)
Mandelbrot200-4            3.82ms ± 3%    3.79ms ± 3%     ~     (p=0.074 n=35+35)
GoParse-4                  3.21ms ± 5%    3.24ms ± 4%     ~     (p=0.119 n=35+35)
RegexpMatchEasy0_32-4      76.3ns ± 4%    75.4ns ± 4%   -1.14%  (p=0.014 n=34+33)
RegexpMatchEasy0_1K-4       251ns ± 4%     254ns ± 3%   +1.28%  (p=0.016 n=35+35)
RegexpMatchEasy1_32-4      69.6ns ± 3%    70.1ns ± 3%   +0.82%  (p=0.005 n=35+35)
RegexpMatchEasy1_1K-4       367ns ± 4%     376ns ± 4%   +2.47%  (p=0.000 n=35+35)
RegexpMatchMedium_32-4      108ns ± 5%     104ns ± 4%   -3.18%  (p=0.000 n=35+35)
RegexpMatchMedium_1K-4     33.8µs ± 3%    32.7µs ± 3%   -3.27%  (p=0.000 n=35+35)
RegexpMatchHard_32-4       1.55µs ± 3%    1.52µs ± 3%   -1.64%  (p=0.000 n=35+35)
RegexpMatchHard_1K-4       46.6µs ± 3%    46.6µs ± 4%     ~     (p=0.149 n=35+35)
Revcomp-4                   416ms ± 7%     412ms ± 6%   -0.95%  (p=0.033 n=33+35)
Template-4                 64.3ms ± 3%    62.4ms ± 7%   -2.94%  (p=0.000 n=35+35)
TimeParse-4                 320ns ± 2%     322ns ± 3%     ~     (p=0.589 n=35+35)
TimeFormat-4                300ns ± 3%     300ns ± 3%     ~     (p=0.597 n=35+35)
[Geo mean]                 47.4µs         47.0µs        -0.86%

name                     old speed      new speed      delta
GobDecode-4               119MB/s ± 7%   118MB/s ± 7%   -0.96%  (p=0.027 n=35+35)
GobEncode-4               126MB/s ± 7%   127MB/s ± 6%     ~     (p=0.157 n=34+34)
Gzip-4                   85.3MB/s ± 3%  87.9MB/s ± 3%   +3.02%  (p=0.000 n=35+35)
Gunzip-4                  518MB/s ± 4%   522MB/s ± 3%   +0.79%  (p=0.037 n=35+35)
JSONEncode-4              162MB/s ± 3%   159MB/s ± 3%   -1.81%  (p=0.009 n=35+35)
JSONDecode-4             34.1MB/s ± 4%  34.3MB/s ± 3%     ~     (p=0.318 n=35+35)
GoParse-4                18.0MB/s ± 5%  17.9MB/s ± 4%     ~     (p=0.117 n=35+35)
RegexpMatchEasy0_32-4     419MB/s ± 3%   425MB/s ± 4%   +1.46%  (p=0.003 n=32+33)
RegexpMatchEasy0_1K-4    4.07GB/s ± 4%  4.02GB/s ± 3%   -1.28%  (p=0.014 n=35+35)
RegexpMatchEasy1_32-4     460MB/s ± 3%   456MB/s ± 4%   -0.82%  (p=0.004 n=35+35)
RegexpMatchEasy1_1K-4    2.79GB/s ± 4%  2.72GB/s ± 4%   -2.39%  (p=0.000 n=35+35)
RegexpMatchMedium_32-4   9.23MB/s ± 4%  9.53MB/s ± 4%   +3.16%  (p=0.000 n=35+35)
RegexpMatchMedium_1K-4   30.3MB/s ± 3%  31.3MB/s ± 3%   +3.38%  (p=0.000 n=35+35)
RegexpMatchHard_32-4     20.7MB/s ± 3%  21.0MB/s ± 3%   +1.67%  (p=0.000 n=35+35)
RegexpMatchHard_1K-4     22.0MB/s ± 3%  21.9MB/s ± 4%     ~     (p=0.277 n=35+33)
Revcomp-4                 612MB/s ± 7%   618MB/s ± 6%   +0.96%  (p=0.034 n=33+35)
Template-4               30.2MB/s ± 3%  31.1MB/s ± 6%   +3.05%  (p=0.000 n=35+35)
[Geo mean]                123MB/s        124MB/s        +0.64%

Change-Id: Ia025da272e07d0069413824bfff3471b106d6280
Reviewed-on: https://go-review.googlesource.com/121535
Run-TryBot: Ben Shi <powerman1st@163.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ilya Tocar <ilya.tocar@intel.com>
Reviewed-by: Keith Randall <khr@golang.org>