decomp: add prefetch for matched seq on aarch64

[JunHe77]

match is used for following sequence copy. It is
only updated when extDict is needed, which is a
low probability case. So it can be prefetched to
reduce cache miss.
The benchmarks on various Arm platforms showed
uplift from 1% ~ 14% with gcc-11/clang-14.

Signed-off-by: Jun He jun.he@arm.com
Change-Id: If201af4799d2455d74c79f8387404439d7f684ae

[JunHe77]

Benchmark changes on Arm N1/A72/A57 with gcc-11:

file	N1/L2	N1/L8	N1/L15	A72/L2	A72/L8	A72/L15	A57/L2	A57/L8	A57/L15
dickens	3.144%	3.869%	3.967%	4.460%	4.389%	11.991%	5.341%	8.165%	12.130%
mr	1.192%	3.658%	3.606%	2.977%	6.147%	13.810%	1.826%	8.634%	12.909%
nci	0.737%	1.070%	1.811%	-0.812%	1.065%	3.879%	0.164%	0.240%	2.399%
ooffice	0.134%	2.445%	2.389%	-0.726%	0.080%	4.424%	-0.306%	3.859%	5.377%
osdb	1.251%	2.669%	3.856%	-0.125%	1.912%	6.158%	0.443%	3.182%	5.333%
reymont	2.639%	2.904%	3.641%	4.097%	3.379%	7.885%	3.649%	5.660%	9.412%
samba	1.129%	1.291%	1.393%	0.589%	1.950%	2.650%	0.758%	1.750%	1.401%
sao	0.728%	2.475%	2.633%	-0.059%	2.364%	6.211%	0.633%	4.288%	6.761%
webster	2.138%	2.952%	2.483%	2.587%	5.809%	8.609%	3.530%	5.328%	7.289%
xml	0.604%	1.010%	0.934%	-0.099%	-0.110%	0.394%	0.497%	0.607%	1.045%
x-ray	0.102%	4.541%	4.543%	-0.159%	6.198%	12.980%	0.102%	11.965%	14.064%

[JunHe77]

Benchmark changes on Arm N1/A72/A57 with clang-14:

file	N1/L2	N1/L8	N1/L15	A72/L2	A72/L8	A72/L15	A57/L2	A57/L8	A57/L15
dickens	2.755%	2.502%	2.235%	5.207%	6.836%	7.938%	5.987%	6.615%	6.607%
mozilla	0.741%	1.053%	1.032%	1.562%	2.610%	2.648%	1.066%	2.305%	2.180%
mr	2.270%	2.156%	2.110%	3.870%	4.890%	7.011%	3.409%	6.377%	6.168%
nci	0.841%	1.464%	2.739%	1.498%	2.558%	3.520%	1.122%	1.473%	2.337%
ooffice	1.103%	1.408%	1.704%	1.451%	3.761%	3.848%	1.181%	3.578%	3.808%
osdb	1.970%	2.545%	2.973%	4.665%	4.347%	5.006%	2.029%	3.241%	2.862%
reymont	2.379%	2.250%	2.490%	3.589%	5.267%	5.028%	4.517%	4.581%	4.335%
samba	1.738%	1.628%	1.501%	4.137%	3.137%	4.069%	2.723%	2.799%	3.032%
sao	0.445%	1.371%	1.314%	3.716%	4.120%	5.453%	1.299%	4.017%	4.459%
webster	2.782%	2.242%	1.893%	5.957%	5.264%	6.333%	4.216%	4.408%	3.738%
xml	1.512%	1.992%	1.557%	2.649%	1.462%	2.174%	2.044%	2.395%	2.080%
x-ray	0.363%	2.357%	2.477%	0.705%	7.155%	6.502%	0.721%	7.207%	6.986%

[JunHe77]

This change may lead to regression on x86. My test on Xeon5218 is:

file	gcc-11/L2	gcc-11/L8	gcc-11/L15	clang-14/L2	clang-14/L8	clang-14/L15
dickens	-2.672%	-3.085%	-3.879%	-0.514%	-1.577%	-3.390%
mozilla	0.813%	0.102%	-0.066%	-0.349%	-0.721%	-1.044%
mr	-1.689%	-3.238%	-5.032%	-0.313%	-1.618%	-3.501%
nci	1.174%	0.675%	1.035%	-0.130%	-0.362%	-0.441%
ooffice	-0.301%	-1.163%	-1.887%	-0.427%	-1.106%	-1.597%
osdb	0.180%	-1.443%	0.655%	-0.138%	-1.137%	1.217%
reymont	-1.821%	-0.914%	-0.781%	-0.493%	-1.264%	-1.666%
samba	-0.278%	-0.388%	-0.472%	-0.195%	-0.410%	-0.463%
sao	-0.037%	-2.148%	-2.747%	-0.184%	-1.062%	-1.971%
webster	-1.548%	-1.107%	-0.989%	-0.576%	-1.172%	-1.560%
xml	0.055%	-0.056%	0.026%	-0.036%	-0.311%	-0.431%
x-ray	-0.155%	-3.566%	-4.536%	-0.028%	-2.175%	-3.596%

[Cyan4973]

I believe this is a rather good policy.
It's surprising that it doesn't work for x64 though (I assume you meant x64 when you stated "x86").

There are a few quirks, such as overlapped prefetch orders when decoding in long mode, or useless prefetching when extDict is present (which might not be captured by benchmark). But these are refinements that can be worked on later on.