On Wed, Sep 11, 2019 at 5:50 PM 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?
Do we document target specific deviations from "default" behavior somewhere?
invoke.texi has
@item -fcode-hoisting
@opindex fcode-hoisting
Perform code hoisting. Code hoisting tries to move the
evaluation of expressions executed on all paths to the function exit
as early as possible. This is especially useful as a code size
optimization, but it often helps for code speed as well.
This flag is enabled by default at @option{-O2} and higher.
> 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 }
> };
>
>
