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[PATCH][AArch64] Update alignment for -mcpu=generic
- From: Wilco Dijkstra <Wilco dot Dijkstra at arm dot com>
- To: GCC Patches <gcc-patches at gcc dot gnu dot org>
- Cc: nd <nd at arm dot com>, James Greenhalgh <James dot Greenhalgh at arm dot com>, "jim dot wilson at linaro dot org" <jim dot wilson at linaro dot org>, Evandro Menezes <e dot menezes at samsung dot com>, "Andrew dot pinski at cavium dot com" <Andrew dot pinski at cavium dot com>
- Date: Wed, 12 Apr 2017 12:58:55 +0000
- Subject: [PATCH][AArch64] Update alignment for -mcpu=generic
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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. */