Add LoongArch SX SIMD extenstion implementation

[lrzlin]

Add LoongArch SX SIMD extension support to xxHash, which is a new RISC ISA just like RISC-V. The code itself is basically a rewritten of the SSE2 one, tested on Loongson 3A6000 processor, here are the results.

Scalar

./xxhsum --benchmark-all
xxhsum 0.8.3 by Yann Collet
compiled as 64-bit unknown little endian with GCC 14.1.1 20240720
Sample of 100 KB...
 1#XXH32                         :     102400 ->    60583 it/s ( 5916.3 MB/s)
 2#XXH32 unaligned               :     102400 ->    58909 it/s ( 5752.8 MB/s)
 3#XXH64                         :     102400 ->   117056 it/s (11431.2 MB/s)
 4#XXH64 unaligned               :     102400 ->   118304 it/s (11553.1 MB/s)
 5#XXH3_64b                      :     102400 ->   142790 it/s (13944.4 MB/s)
 6#XXH3_64b unaligned            :     102400 ->   136549 it/s (13334.9 MB/s)
 7#XXH3_64b w/seed               :     102400 ->   117327 it/s (11457.8 MB/s)
 8#XXH3_64b w/seed unaligned     :     102400 ->   114720 it/s (11203.1 MB/s)
 9#XXH3_64b w/secret             :     102400 ->   144445 it/s (14106.0 MB/s)
10#XXH3_64b w/secret unaligned   :     102400 ->   138076 it/s (13483.9 MB/s)
11#XXH128                        :     102400 ->   114568 it/s (11188.3 MB/s)
12#XXH128 unaligned              :     102400 ->   111621 it/s (10900.5 MB/s)
13#XXH128 w/seed                 :     102400 ->   144003 it/s (14062.8 MB/s)
14#XXH128 w/seed unaligned       :     102400 ->   137411 it/s (13419.1 MB/s)
15#XXH128 w/secret               :     102400 ->   151320 it/s (14777.3 MB/s)
16#XXH128 w/secret unaligned     :     102400 ->   143261 it/s (13990.4 MB/s)
17#XXH32_stream                  :     102400 ->    60783 it/s ( 5935.8 MB/s)
18#XXH32_stream unaligned        :     102400 ->    56481 it/s ( 5515.7 MB/s)
19#XXH64_stream                  :     102400 ->   116072 it/s (11335.1 MB/s)
20#XXH64_stream unaligned        :     102400 ->   105525 it/s (10305.2 MB/s)
21#XXH3_stream                   :     102400 ->   116267 it/s (11354.2 MB/s)
22#XXH3_stream unaligned         :     102400 ->   112994 it/s (11034.6 MB/s)
23#XXH3_stream w/seed            :     102400 ->   115983 it/s (11326.5 MB/s)
24#XXH3_stream w/seed unaligned  :     102400 ->   112852 it/s (11020.7 MB/s)
25#XXH128_stream                 :     102400 ->   116232 it/s (11350.8 MB/s)
26#XXH128_stream unaligned       :     102400 ->   112905 it/s (11025.8 MB/s)
27#XXH128_stream w/seed          :     102400 ->   116081 it/s (11336.1 MB/s)
28#XXH128_stream w/seed unaligne :     102400 ->   112789 it/s (11014.6 MB/s)

LoongArch SX

./xxhsum --benchmark-all
xxhsum 0.8.3 by Yann Collet
compiled as 64-bit loongarch little endian with GCC 14.1.1 20240720
Sample of 100 KB...
 1#XXH32                         :     102400 ->    60569 it/s ( 5915.0 MB/s)
 2#XXH32 unaligned               :     102400 ->    58907 it/s ( 5752.6 MB/s)
 3#XXH64                         :     102400 ->   117053 it/s (11431.0 MB/s)
 4#XXH64 unaligned               :     102400 ->   118289 it/s (11551.6 MB/s)
 5#XXH3_64b                      :     102400 ->   199076 it/s (19441.0 MB/s)
 6#XXH3_64b unaligned            :     102400 ->   189993 it/s (18554.0 MB/s)
 7#XXH3_64b w/seed               :     102400 ->   199722 it/s (19504.1 MB/s)
 8#XXH3_64b w/seed unaligned     :     102400 ->   189672 it/s (18522.7 MB/s)
 9#XXH3_64b w/secret             :     102400 ->   183999 it/s (17968.7 MB/s)
10#XXH3_64b w/secret unaligned   :     102400 ->   176080 it/s (17195.3 MB/s)
11#XXH128                        :     102400 ->   198883 it/s (19422.2 MB/s)
12#XXH128 unaligned              :     102400 ->   189925 it/s (18547.3 MB/s)
13#XXH128 w/seed                 :     102400 ->   198877 it/s (19421.6 MB/s)
14#XXH128 w/seed unaligned       :     102400 ->   188807 it/s (18438.2 MB/s)
15#XXH128 w/secret               :     102400 ->   183770 it/s (17946.3 MB/s)
16#XXH128 w/secret unaligned     :     102400 ->   175811 it/s (17169.0 MB/s)
17#XXH32_stream                  :     102400 ->    60782 it/s ( 5935.7 MB/s)
18#XXH32_stream unaligned        :     102400 ->    56488 it/s ( 5516.4 MB/s)
19#XXH64_stream                  :     102400 ->   116075 it/s (11335.4 MB/s)
20#XXH64_stream unaligned        :     102400 ->   105448 it/s (10297.7 MB/s)
21#XXH3_stream                   :     102400 ->   199438 it/s (19476.4 MB/s)
22#XXH3_stream unaligned         :     102400 ->   190148 it/s (18569.2 MB/s)
23#XXH3_stream w/seed            :     102400 ->   198714 it/s (19405.7 MB/s)
24#XXH3_stream w/seed unaligned  :     102400 ->   189577 it/s (18513.3 MB/s)
25#XXH128_stream                 :     102400 ->   199140 it/s (19447.3 MB/s)
26#XXH128_stream unaligned       :     102400 ->   190063 it/s (18560.8 MB/s)
27#XXH128_stream w/seed          :     102400 ->   198738 it/s (19408.0 MB/s)
28#XXH128_stream w/seed unaligne :     102400 ->   189668 it/s (18522.3 MB/s)

Reference
LoongArch Intrinsics Document: https://jia.je/unofficial-loongarch-intrinsics-guide/

Resolve
loongson-community/discussions#72