cmd/compile: implement CMOV on amd64

cmd/compile: implement CMOV on amd64

This builds upon the branchelim pass, activating it for amd64 and
lowering CondSelect. Special care is made to FPU instructions for
NaN handling.

Benchmark results on Xeon E5630 (Westmere EP):

name                      old time/op    new time/op    delta
BinaryTree17-16              4.99s ± 9%     4.66s ± 2%     ~     (p=0.095 n=5+5)
Fannkuch11-16                4.93s ± 3%     5.04s ± 2%     ~     (p=0.548 n=5+5)
FmtFprintfEmpty-16          58.8ns ± 7%    61.4ns ±14%     ~     (p=0.579 n=5+5)
FmtFprintfString-16          114ns ± 2%     114ns ± 4%     ~     (p=0.603 n=5+5)
FmtFprintfInt-16             181ns ± 4%     125ns ± 3%  -30.90%  (p=0.008 n=5+5)
FmtFprintfIntInt-16          263ns ± 2%     217ns ± 2%  -17.34%  (p=0.008 n=5+5)
FmtFprintfPrefixedInt-16     230ns ± 1%     212ns ± 1%   -7.99%  (p=0.008 n=5+5)
FmtFprintfFloat-16           411ns ± 3%     344ns ± 5%  -16.43%  (p=0.008 n=5+5)
FmtManyArgs-16               828ns ± 4%     790ns ± 2%   -4.59%  (p=0.032 n=5+5)
GobDecode-16                10.9ms ± 4%    10.8ms ± 5%     ~     (p=0.548 n=5+5)
GobEncode-16                9.52ms ± 5%    9.46ms ± 2%     ~     (p=1.000 n=5+5)
Gzip-16                      334ms ± 2%     337ms ± 2%     ~     (p=0.548 n=5+5)
Gunzip-16                   64.4ms ± 1%    65.0ms ± 1%   +1.00%  (p=0.008 n=5+5)
HTTPClientServer-16          156µs ± 3%     155µs ± 3%     ~     (p=0.690 n=5+5)
JSONEncode-16               21.0ms ± 1%    21.8ms ± 0%   +3.76%  (p=0.016 n=5+4)
JSONDecode-16               95.1ms ± 0%    95.7ms ± 1%     ~     (p=0.151 n=5+5)
Mandelbrot200-16            6.38ms ± 1%    6.42ms ± 1%     ~     (p=0.095 n=5+5)
GoParse-16                  5.47ms ± 2%    5.36ms ± 1%   -1.95%  (p=0.016 n=5+5)
RegexpMatchEasy0_32-16       111ns ± 1%     111ns ± 1%     ~     (p=0.635 n=5+4)
RegexpMatchEasy0_1K-16       408ns ± 1%     411ns ± 2%     ~     (p=0.087 n=5+5)
RegexpMatchEasy1_32-16       103ns ± 1%     104ns ± 1%     ~     (p=0.484 n=5+5)
RegexpMatchEasy1_1K-16       659ns ± 2%     652ns ± 1%     ~     (p=0.571 n=5+5)
RegexpMatchMedium_32-16      176ns ± 2%     174ns ± 1%     ~     (p=0.476 n=5+5)
RegexpMatchMedium_1K-16     58.6µs ± 4%    57.7µs ± 4%     ~     (p=0.548 n=5+5)
RegexpMatchHard_32-16       3.07µs ± 3%    3.04µs ± 4%     ~     (p=0.421 n=5+5)
RegexpMatchHard_1K-16       89.2µs ± 1%    87.9µs ± 2%   -1.52%  (p=0.032 n=5+5)
Revcomp-16                   575ms ± 0%     587ms ± 2%   +2.12%  (p=0.032 n=4+5)
Template-16                  110ms ± 1%     107ms ± 3%   -3.00%  (p=0.032 n=5+5)
TimeParse-16                 463ns ± 0%     462ns ± 0%     ~     (p=0.810 n=5+4)
TimeFormat-16                538ns ± 0%     535ns ± 0%   -0.63%  (p=0.024 n=5+5)

name                      old speed      new speed      delta
GobDecode-16              70.7MB/s ± 4%  71.4MB/s ± 5%     ~     (p=0.452 n=5+5)
GobEncode-16              80.7MB/s ± 5%  81.2MB/s ± 2%     ~     (p=1.000 n=5+5)
Gzip-16                   58.2MB/s ± 2%  57.7MB/s ± 2%     ~     (p=0.452 n=5+5)
Gunzip-16                  302MB/s ± 1%   299MB/s ± 1%   -0.99%  (p=0.008 n=5+5)
JSONEncode-16             92.4MB/s ± 1%  89.1MB/s ± 0%   -3.63%  (p=0.016 n=5+4)
JSONDecode-16             20.4MB/s ± 0%  20.3MB/s ± 1%     ~     (p=0.135 n=5+5)
GoParse-16                10.6MB/s ± 2%  10.8MB/s ± 1%   +2.00%  (p=0.016 n=5+5)
RegexpMatchEasy0_32-16     286MB/s ± 1%   285MB/s ± 3%     ~     (p=1.000 n=5+5)
RegexpMatchEasy0_1K-16    2.51GB/s ± 1%  2.49GB/s ± 2%     ~     (p=0.095 n=5+5)
RegexpMatchEasy1_32-16     309MB/s ± 1%   307MB/s ± 1%     ~     (p=0.548 n=5+5)
RegexpMatchEasy1_1K-16    1.55GB/s ± 2%  1.57GB/s ± 1%     ~     (p=0.690 n=5+5)
RegexpMatchMedium_32-16   5.68MB/s ± 2%  5.73MB/s ± 1%     ~     (p=0.579 n=5+5)
RegexpMatchMedium_1K-16   17.5MB/s ± 4%  17.8MB/s ± 4%     ~     (p=0.500 n=5+5)
RegexpMatchHard_32-16     10.4MB/s ± 3%  10.5MB/s ± 4%     ~     (p=0.460 n=5+5)
RegexpMatchHard_1K-16     11.5MB/s ± 1%  11.7MB/s ± 2%   +1.57%  (p=0.032 n=5+5)
Revcomp-16                 442MB/s ± 0%   433MB/s ± 2%   -2.05%  (p=0.032 n=4+5)
Template-16               17.7MB/s ± 1%  18.2MB/s ± 3%   +3.12%  (p=0.032 n=5+5)

Change-Id: Ic7cb7374d07da031e771bdcbfdd832fd1b17159c
Reviewed-on: https://go-review.googlesource.com/98695
Reviewed-by: Ilya Tocar <ilya.tocar@intel.com>