On Wed, 11 Sep 2019 at 11:50, Wilco Dijkstra <wilco.dijks...@arm.com> wrote:
>
> While code hoisting generally improves codesize, it can affect performance
> negatively. Benchmarking shows it doesn't help SPEC and negatively affects
> embedded benchmarks, so only enable code hoisting with -Os on Arm.
>
> Bootstrap OK, OK for commit?
Hi Wilco,
My only concern with the patch is that the issue isn't specific to
code-hoisting.
For this particular case (reproducible with pr77445-2.c), disabling
jump threading
doesn't cause the register spill with hoisting enabled.
Likewise disabling forwprop3 and forwprop4 prevents the spill.
The last time I tried, setting setting
max-jump-thread-duplication-stmts to 20 and
fsm-scale-path-stmts to 3, not only removed the spill but also
resulted in 9 more hoistings,
but regressed some other test on jump threading.
So I was wondering whether we should look into fine-tuning relevant params,
instead of disabling code hoisting entirely (we will end up regressing
some test cases either way) ?
Thanks,
Prathamesh
>
> ChangeLog:
> 2019-09-11 Wilco Dijkstra <wdijk...@arm.com>
>
>
> PR tree-optimization/80155
> * common/config/arm/arm-common.c (arm_option_optimization_table):
> Enable -fcode-hoisting with -Os.
>
> --
> diff --git a/gcc/common/config/arm/arm-common.c
> b/gcc/common/config/arm/arm-common.c
> index
> 41a920f6dc96833e778faa8dbcc19beac483734c..b0d5fb300bf01acc1fb6f4631635f8a1bfe6441c
> 100644
> --- a/gcc/common/config/arm/arm-common.c
> +++ b/gcc/common/config/arm/arm-common.c
> @@ -39,6 +39,8 @@ static const struct default_options
> arm_option_optimization_table[] =
> /* Enable section anchors by default at -O1 or higher. */
> { OPT_LEVELS_1_PLUS, OPT_fsection_anchors, NULL, 1 },
> { OPT_LEVELS_1_PLUS, OPT_fsched_pressure, NULL, 1 },
> + /* Enable code hoisting only with -Os. */
> + { OPT_LEVELS_SIZE, OPT_fcode_hoisting, NULL, 1 },
> { OPT_LEVELS_NONE, 0, NULL, 0 }
> };
>
>
