[PATCH] AArch64: Enable fast shifts on Neoverse N1

[Wilco Dijkstra]

Enable the fast shift feature in Neoverse N1 tuning - this means additions with
a shift left by 1-4 are as fast as addition. This improves multiply by constant
expansions, eg. x * 25 is now emitted using shifts rather than a multiply:

add w0, w0, w0, lsl 2
add w0, w0, w0, lsl 2

Bootstrap OK, regress pass, OK for commit?

ChangeLog:
2020-09-11  Wilco Dijkstra  <wdijk...@arm.com>

        * config/aarch64/aarch64.c (neoversen1_tunings):
        Enable AARCH64_EXTRA_TUNE_CHEAP_SHIFT_EXTEND.

---

diff --git a/gcc/config/aarch64/aarch64.c b/gcc/config/aarch64/aarch64.c
index 
803562df25751f2eb6dbe18b67cae46ea7c478dd..cbbdefa436bf11e9631c90631fb621e90e60754a
 100644
--- a/gcc/config/aarch64/aarch64.c
+++ b/gcc/config/aarch64/aarch64.c
@@ -1332,7 +1332,7 @@ static const struct tune_params neoversen1_tunings =
   2,   /* min_div_recip_mul_df.  */
   0,   /* max_case_values.  */
   tune_params::AUTOPREFETCHER_WEAK,    /* autoprefetcher_model.  */
-  (AARCH64_EXTRA_TUNE_NONE),   /* tune_flags.  */
+  (AARCH64_EXTRA_TUNE_CHEAP_SHIFT_EXTEND),     /* tune_flags.  */
   &generic_prefetch_tune
 };