[PATCH][ARM] Update max_cond_insns settings

[Wilco Dijkstra]

ping


From: Wilco Dijkstra
Sent: 12 April 2017 14:02
To: GCC Patches
Cc: nd; Kyrylo Tkachov
Subject: [PATCH][ARM] Update max_cond_insns settings
    
The existing setting of max_cond_insns for most cores is non-optimal.
Thumb-2 IT has a maximum limit of 4, so 5 means emitting 2 IT sequences.
Also such long sequences of conditional instructions can increase the number
of executed instructions significantly, so using 5 for max_cond_insns is
non-optimal.

Previous benchmarking showed that setting max_cond_insn to 2 was the best value
for Cortex-A15 and Cortex-A57.  All ARMv8-A cores use 2 - apart from Cortex-A35
and Cortex-A53.  Given that using 5 is worse, set it to 2.  This also has the
advantage of producing more uniform code.

Bootstrap and regress OK on arm-none-linux-gnueabihf.

OK for stage 1?

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

        * gcc/config/arm/arm.c (arm_cortex_a53_tune): Set max_cond_insns to 2.
        (arm_cortex_a35_tune): Likewise.
---

diff --git a/gcc/config/arm/arm.c b/gcc/config/arm/arm.c
index 29e8d1d07d918fbb2a627a653510dfc8587ee01a..1a6d552aa322114795acbb3667c6ea36963bf193 100644
--- a/gcc/config/arm/arm.c
+++ b/gcc/config/arm/arm.c
@@ -1967,7 +1967,7 @@ const struct tune_params arm_cortex_a35_tune =
   arm_default_branch_cost,
   &arm_default_vec_cost,
   1,                                           /* Constant limit.  */
-  5,                                           /* Max cond insns.  */
+  2,                                           /* Max cond insns.  */
   8,                                           /* Memset max inline.  */
   1,                                           /* Issue rate.  */
   ARM_PREFETCH_NOT_BENEFICIAL,
@@ -1990,7 +1990,7 @@ const struct tune_params arm_cortex_a53_tune =
   arm_default_branch_cost,
   &arm_default_vec_cost,
   1,                                           /* Constant limit.  */
-  5,                                           /* Max cond insns.  */
+  2,                                           /* Max cond insns.  */
   8,                                           /* Memset max inline.  */
   2,                                           /* Issue rate.  */
   ARM_PREFETCH_NOT_BENEFICIAL,