On 06/20/2018 05:16 PM, Jeff Law wrote:
> On 06/20/2018 05:25 AM, Steven Bosscher wrote:
>> On Tue, Jun 12, 2018 at 10:44 PM, Jeff Law wrote:
>>> On 06/05/2018 01:15 AM, marxin wrote:
>>>>
>>>> + The definition of "much bigger" depends on whether we are
>>>> + optimizing for size or for speed. If the former, the maximum
>>>> + ratio range/count = 3, because this was found to be the optimal
>>>> + ratio for size on i686-pc-linux-gnu, see PR11823. The ratio
>>>> + 10 is much older, and was probably selected after an extensive
>>>> + benchmarking investigation on numerous platforms. Or maybe it
>>>> + just made sense to someone at some point in the history of GCC,
>>>> + who knows... */
>>> "much older" is an understatement. I believe the magic "10" pre-dates
>>> my involvement in GCC. You can find evidence of it as far back as
>>> gcc-0.9. I doubt it was extensively benchmarked, and even if it was,
>>> the targets on which it was benchmarked don't reflect modern target
>>> reality in terms of importance.
>>
>> When I added this comment
>> (https://gcc.gnu.org/viewcvs/gcc/trunk/gcc/stmt.c?r1=189284&r2=189285&;)
>> it as an attempt at humor. I should have turned the number into a
>> PARAM at the time. Maybe that's something Martin could still do now?
> A PARAM feels like overkill, but I certainly wouldn't object. I'd be
> happy with that, a const member in the class or even the adjusted
> constant.
>
> jeff
>
Hi.
Agree with Jeff, there's a patch that does that.
Ready after it finishes tests?
Martin
>From 27d7c87720dc464b6ed998bc7344cf2226d5f9ea Mon Sep 17 00:00:00 2001
From: marxin <mli...@suse.cz>
Date: Fri, 22 Jun 2018 12:24:13 +0200
Subject: [PATCH] Come up with jump_table ratio constants used in
jump_table_cluster.
gcc/ChangeLog:
2018-06-22 Martin Liska <mli...@suse.cz>
* tree-switch-conversion.c (jump_table_cluster::can_be_handled):
Use newly introduced constants.
* tree-switch-conversion.h (struct jump_table_cluster):
Define max_ratio_for_size and max_ratio_for_speed.
---
gcc/tree-switch-conversion.c | 3 ++-
gcc/tree-switch-conversion.h | 6 ++++++
2 files changed, 8 insertions(+), 1 deletion(-)
diff --git a/gcc/tree-switch-conversion.c b/gcc/tree-switch-conversion.c
index ddd8cba7b98..b79f2fdb6e6 100644
--- a/gcc/tree-switch-conversion.c
+++ b/gcc/tree-switch-conversion.c
@@ -1180,7 +1180,8 @@ jump_table_cluster::can_be_handled (const vec<cluster *> &clusters,
if (start == end)
return true;
- unsigned HOST_WIDE_INT max_ratio = optimize_insn_for_size_p () ? 3 : 8;
+ unsigned HOST_WIDE_INT max_ratio
+ = optimize_insn_for_size_p () ? max_ratio_for_size : max_ratio_for_speed;
unsigned HOST_WIDE_INT range = get_range (clusters[start]->get_low (),
clusters[end]->get_high ());
/* Check overflow. */
diff --git a/gcc/tree-switch-conversion.h b/gcc/tree-switch-conversion.h
index 79a1320c448..4beac785f05 100644
--- a/gcc/tree-switch-conversion.h
+++ b/gcc/tree-switch-conversion.h
@@ -257,6 +257,12 @@ struct jump_table_cluster: public group_cluster
/* Return whether jump table expansion is allowed. */
static bool is_enabled (void);
+
+ /* Max growth ratio for code that is optimized for size. */
+ static const unsigned HOST_WIDE_INT max_ratio_for_size = 3;
+
+ /* Max growth ratio for code that is optimized for speed. */
+ static const unsigned HOST_WIDE_INT max_ratio_for_speed = 8;
};
/* A GIMPLE switch statement can be expanded to a short sequence of bit-wise
--
2.17.1
