Re: [PATCH][AArch64] Update alignment for -mcpu=generic

[Wilco Dijkstra <Wilco.Dijkstra@arm.com>]

ping


From: Wilco Dijkstra
Sent: 12 April 2017 13:58
To: GCC Patches
Cc: nd; James Greenhalgh; jim.wilson@linaro.org; Evandro Menezes; Andrew.pinski@cavium.com
Subject: [PATCH][AArch64] Update alignment for -mcpu=generic
    
With -mcpu=generic the loop alignment is currently 4.  All but one of the
supported cores use 8 or higher.  Since using 8 provides performance gains
on several cores, it is best to use that by default.  As discussed in [1],
the jump alignment has no effect on performance, yet has a relatively high
codesize cost [2], so setting it to 4 is best.  This gives a 0.2% overall 
codesize improvement as well as performance gains in several benchmarks.
Any objections?

Bootstrap OK on AArch64, OK for stage 1?

ChangeLog:
2017-04-12  Wilco Dijkstra  <wdijkstr@arm.com>

        * config/aarch64/aarch64.c (generic_tunings): Set jump alignment to 4.
        Set loop alignment to 8.

[1] https://gcc.gnu.org/ml/gcc-patches/2017-04/msg00574.html
[2] https://gcc.gnu.org/ml/gcc-patches/2016-06/msg02075.html

---
diff --git a/gcc/config/aarch64/aarch64.c b/gcc/config/aarch64/aarch64.c
index c8cf7169a5d387de336920b50c83761dc0c96f3a..8b729b1b1f87316e940d7fc657f235a935ffa93e 100644
--- a/gcc/config/aarch64/aarch64.c
+++ b/gcc/config/aarch64/aarch64.c
@@ -538,8 +538,8 @@ static const struct tune_params generic_tunings =
   2, /* issue_rate  */
   (AARCH64_FUSE_AES_AESMC), /* fusible_ops  */
   8,   /* function_align.  */
-  8,   /* jump_align.  */
-  4,   /* loop_align.  */
+  4,   /* jump_align.  */
+  8,   /* loop_align.  */
   2,   /* int_reassoc_width.  */
   4,   /* fp_reassoc_width.  */
   1,   /* vec_reassoc_width.  */