Do not use AVX2 instructions if the CPU doesn't support it

[edwintorok]

The code for checking CPUID and alternate non-avx2 implementations were all mostly in place, except:

• xgetbv was used before checking CPUID, which caused a SIGILL
• the AVX2 codepath was used due to incorrect use of the PREAVX2_MASK flag (it always picked the avx2 path, even on non-avx2 cpus)

Fixes #9

This code is part of the Phoronix test suite, and I noticed that it crashed on AMD Opteron Processor 6172, now it no longer crashes:

./SVT-VP9/Bin/Release/SvtVp9EncApp -i Bosphorus_1920x1080_120fps_420_8bit_YUV.yuv -w 1920 -h 1080
-------------------------------------
SVT-VP9 Encoder v0.1.0
SVT [version]   : SVT-VP9 Encoder Lib v0.1.0
SVT [build]     : GCC 6.3.0      64 bit
LIB Build date: Oct 16 2019 15:36:57
-------------------------------------------
Number of logical cores available: 24
Number of PPCS 75
------------------------------------------- 
SVT [config]: Profile [0]       Level (auto)    
SVT [config]: EncoderMode / Tune                                                : 9 / 1 
SVT [config]: EncoderBitDepth                                                   : 8 
SVT [config]: SourceWidth / SourceHeight                                        : 1920 / 1080 
SVT [config]: FrameRate / Gop Size                                              : 60 / 64 
SVT [config]: HierarchicalLevels / BaseLayerSwitchMode / PredStructure          : 4 / 0 / 2 
SVT [config]: BRC Mode / QP                                                     : CQP / 45 
------------------------------------------- 


Encoding       600
SUMMARY --------------------------------- Channel 1  --------------------------------
Total Frames            Frame Rate              Byte Count              Bitrate
         600            60.00 fps                  3178622              2542.90 kbps


Channel 1
Average Speed:          8.90 fps
Total Encoding Time:    67391 ms
Total Execution Time:   68054 ms
Average Latency:        12944 ms
Max Latency:            17889 ms
Encoder finished

Note: other SVT projects suffer from same problem:

Oct 10 09:52:32 localhost kernel: [21674.538922] traps: SvtAv1EncApp[71948] trap invalid opcode ip:7f53d9187db1 sp:7f531a25c2a8 error:0
Oct 10 09:52:32 localhost kernel: [21674.540087]  in libSvtAv1Enc.so.0.7.0[7f53d8f35000+426000]
Oct 10 09:52:38 localhost kernel: [21680.858543] traps: SvtAv1EncApp[71970] trap invalid opcode ip:7f9fecf89db1 sp:7f9f2e05e2a8 error:0
Oct 10 09:52:38 localhost kernel: [21680.859492]  in libSvtAv1Enc.so.0.7.0[7f9fecd37000+426000]
Oct 10 09:52:45 localhost kernel: [21687.190615] traps: SvtAv1EncApp[72002] trap invalid opcode ip:7f06fb014db1 sp:7f063c0e92a8 error:0
Oct 10 09:52:45 localhost kernel: [21687.191559]  in libSvtAv1Enc.so.0.7.0[7f06fadc2000+426000]
Oct 10 09:52:56 localhost kernel: [21698.790049] traps: SvtAv1EncApp[72024] trap invalid opcode ip:7f960023adb1 sp:7f953289e2a8 error:0
Oct 10 09:52:56 localhost kernel: [21698.790995]  in libSvtAv1Enc.so.0.7.0[7f95fffe8000+426000]
Oct 10 09:53:02 localhost kernel: [21704.346125] traps: SvtAv1EncApp[72046] trap invalid opcode ip:7faf63669db1 sp:7fae95ccd2a8 error:0
Oct 10 09:53:02 localhost kernel: [21704.347072]  in libSvtAv1Enc.so.0.7.0[7faf63417000+426000]
Oct 10 09:53:07 localhost kernel: [21709.915184] traps: SvtAv1EncApp[72068] trap invalid opcode ip:7fe10dc54db1 sp:7fe0402b82a8 error:0
Oct 10 09:53:07 localhost kernel: [21709.916143]  in libSvtAv1Enc.so.0.7.0[7fe10da02000+426000]
Oct 10 09:53:19 localhost kernel: [21721.238068] traps: SvtAv1EncApp[72090] trap invalid opcode ip:7f73bec54db1 sp:7f72f12b82a8 error:0
Oct 10 09:53:19 localhost kernel: [21721.239006]  in libSvtAv1Enc.so.0.7.0[7f73bea02000+426000]
Oct 10 09:53:24 localhost kernel: [21726.535248] traps: SvtAv1EncApp[72112] trap invalid opcode ip:7fdf8bee5db1 sp:7fdebe5492a8 error:0
Oct 10 09:53:24 localhost kernel: [21726.536234]  in libSvtAv1Enc.so.0.7.0[7fdf8bc93000+426000]
Oct 10 09:53:29 localhost kernel: [21731.826031] traps: SvtAv1EncApp[72134] trap invalid opcode ip:7fd42dfd3db1 sp:7fd3606372a8 error:0
Oct 10 09:53:29 localhost kernel: [21731.826972]  in libSvtAv1Enc.so.0.7.0[7fd42dd81000+426000]
Oct 10 09:53:40 localhost kernel: [21742.131875] traps: SvtHevcEncApp[72152] trap invalid opcode ip:7f403535e8e2 sp:7ffe823fee18 error:0
Oct 10 09:53:40 localhost kernel: [21742.132861]  in libSvtHevcEnc.so.1[7f4035343000+382000]
Oct 10 09:53:44 localhost kernel: [21746.240475] traps: SvtHevcEncApp[72165] trap invalid opcode ip:7fc93648d8e2 sp:7ffd20bc3f58 error:0
Oct 10 09:53:44 localhost kernel: [21746.241422]  in libSvtHevcEnc.so.1[7fc936472000+382000]
Oct 10 09:53:48 localhost kernel: [21750.352681] traps: SvtHevcEncApp[72168] trap invalid opcode ip:7f0e777f48e2 sp:7fff06b84988 error:0
Oct 10 09:53:48 localhost kernel: [21750.353631]  in libSvtHevcEnc.so.1[7f0e777d9000+382000]
Oct 10 09:53:58 localhost kernel: [21760.547172] traps: SvtVp9EncApp[72171] trap invalid opcode ip:7f05a7948328 sp:7fffea3f6840 error:0
Oct 10 09:53:58 localhost kernel: [21760.548142]  in libSvtVp9Enc.so.1[7f05a793a000+106000]
Oct 10 09:54:02 localhost kernel: [21764.660897] traps: SvtVp9EncApp[72174] trap invalid opcode ip:7f4cc37ab328 sp:7ffecdb04ee0 error:0
Oct 10 09:54:02 localhost kernel: [21764.661837]  in libSvtVp9Enc.so.1[7f4cc379d000+106000]
Oct 10 09:54:06 localhost kernel: [21768.777223] traps: SvtVp9EncApp[72177] trap invalid opcode ip:7f0c44e87328 sp:7fff6b198c00 error:0
Oct 10 09:54:06 localhost kernel: [21768.778171]  in libSvtVp9Enc.so.1[7f0c44e79000+106000]

[edwintorok]

Is there a test suite I could run to check whether it also works correctly?

[tianjunwork]

Hi @edwintorok, thank you for this PR.
There isn't a full test suite for VP9. We can fork one from HEVC and change from there. I will keep you updated.

[edwintorok]

The appveyor CI error seems unrelated:

Maximum allowed artifact storage size of 50000 Mb will be exceeded.

[tianjunwork]

Hi @edwintorok, yes, it is not related.

[tianjunwork]

Hi @edwintorok, fyi, before merging this PR, there is some effort to evaluate performance on legacy CPU. With the scarcity of legacy HW, it will take longer for us to move forward with this PR.