[PATCH][AArch64] Enable AUTOPREFETCHER_WEAK with -mcpu=generic

[Wilco Dijkstra]

Many supported cores use the AUTOPREFETCHER_WEAK setting which tries
to order loads and stores to improve streaming performance.  Since significant
gains were reported in http://patchwork.ozlabs.org/patch/534469/ it seems
like a good idea to enable this setting too for -mcpu=generic.  Since the
weak model only keeps the order if it doesn't make the schedule worse, it
should not impact performance adversely on cores that don't show a gain.
Any objections?

ChangeLog:
2017-04-05  Wilco Dijkstra  <wdijk...@arm.com>

        * gcc/config/aarch64/aarch64.c (generic_tunings): Update prefetch model.

--
diff --git a/gcc/config/aarch64/aarch64.c b/gcc/config/aarch64/aarch64.c
index 
8b729b1b1f87316e940d7fc657f235a935ffa93e..b249ce2b310707c7ded2827d505ce2ddfcfbf976
 100644
--- a/gcc/config/aarch64/aarch64.c
+++ b/gcc/config/aarch64/aarch64.c
@@ -547,7 +547,7 @@ static const struct tune_params generic_tunings =
   2,   /* min_div_recip_mul_df.  */
   0,   /* max_case_values.  */
   0,   /* cache_line_size.  */
-  tune_params::AUTOPREFETCHER_OFF,     /* autoprefetcher_model.  */
+  tune_params::AUTOPREFETCHER_WEAK,    /* autoprefetcher_model.  */
   (AARCH64_EXTRA_TUNE_NONE)    /* tune_flags.  */
 };