[AArch64] Adjust tuning parameters for Falkor

Disabling software prefetching and switching the autoprefetcher to weak improves
CPU2017 rate and speed benchmarks for both int and fp sets on Falkor.

SPECrate 2017 fp is up 0.38%
SPECspeed 2017 fp is up 0.54%
SPECrate 2017 int is up 3.02%
SPECspeed 2017 int is up 3.16%

There are only a couple individual regressions. The biggest one being about 4%
in parest.

For SPEC2006, we've noticed the following:

SPECint is up 0.91%
SPECfp is stable

In the case of SPEC2006 we noticed both a big regression in mcf (about 20%)
and a big improvement for hmmer (about 40%).

Since the overall result is positive, we would like to make these new tuning
settings the default for Falkor.

We may revisit the software prefetcher setting in the future, in case we
can adjust it enough so it provides us a good balance between improvements and
regressions (mcf). But for now it is best if it stays off.

2017-11-17  Luis Machado  <luis.machado@linaro.org>

	gcc/
	* config/aarch64/aarch64.c
	(qdf24xx_prefetch_tune) <default_opt_level>: Set to -1.
	(qdf24xx_tunings) <autoprefetcher_model>: Set to
	tune_params::AUTOPREFETCHER_WEAK.

From-SVN: r254879

gcc/ChangeLog

+2017-11-17  Luis Machado  <luis.machado@linaro.org>
+
+	* config/aarch64/aarch64.c
+	(qdf24xx_prefetch_tune) <default_opt_level>: Set to -1.
+	(qdf24xx_tunings) <autoprefetcher_model>: Set to
+	tune_params::AUTOPREFETCHER_WEAK.
+
 2017-11-17  Tamar Christina  <tamar.christina@arm.com>
 
 	PR target/82641

gcc/config/aarch64/aarch64.c

@@ -508,7 +508,7 @@ static const cpu_prefetch_tune qdf24xx_prefetch_tune =
   32,			/* l1_cache_size  */
   64,			/* l1_cache_line_size  */
   1024,			/* l2_cache_size  */
-  3			/* default_opt_level  */
+  -1			/* default_opt_level  */
 };
 
 static const cpu_prefetch_tune thunderxt88_prefetch_tune =
@@ -817,7 +817,7 @@ static const struct tune_params qdf24xx_tunings =
   2,	/* min_div_recip_mul_sf.  */
   2,	/* min_div_recip_mul_df.  */
   0,	/* max_case_values.  */
-  tune_params::AUTOPREFETCHER_STRONG,	/* autoprefetcher_model.  */
+  tune_params::AUTOPREFETCHER_WEAK,	/* autoprefetcher_model.  */
   (AARCH64_EXTRA_TUNE_NONE),		/* tune_flags.  */
   &qdf24xx_prefetch_tune
 };