On Fri, Sep 6, 2019 at 10:11 AM Andreas Krebbel <kreb...@linux.ibm.com> wrote:
>
> Hi,
>
> since this caused a critical performance regression in the OpenJ9 byte code
> interpreter after
> migrating from GCC 4.8 to GCC 7 I would like to backport this patch also to
> GCC 8 and 9 branch.
>
> Ok - after bootstrap and regression test went fine?
Looks reasonable to me. But what about GCC 7? I assume you also verified the
actual performance regression is gone.
Richard.
>
> Andreas
>
>
> commit d3dc20418aad41af83fe45ccba527deb0b334983
> Author: krebbel <krebbel@138bc75d-0d04-0410-961f-82ee72b054a4>
> Date: Thu Jun 6 11:35:04 2019 +0000
>
> Fix PR88751
>
> This patch implements a small improvement for the heuristic in lra
> which decides when it has to activate the simpler register allocation
> algorithm.
>
> gcc/ChangeLog:
>
> 2019-06-06 Andreas Krebbel <kreb...@linux.ibm.com>
>
> PR rtl-optimization/88751
> * ira.c (ira): Use the number of the actually referenced registers
> when calculating the threshold.
>
>
>
> git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@271996
> 138bc75d-0d04-0410-961f-82ee72b054a4
>
>
> diff --git a/gcc/ira.c b/gcc/ira.c
> index 4a14fb31583..725636d8dc5 100644
> --- a/gcc/ira.c
> +++ b/gcc/ira.c
> @@ -5198,6 +5198,8 @@ ira (FILE *f)
> int ira_max_point_before_emit;
> bool saved_flag_caller_saves = flag_caller_saves;
> enum ira_region saved_flag_ira_region = flag_ira_region;
> + unsigned int i;
> + int num_used_regs = 0;
>
> clear_bb_flags ();
>
> @@ -5213,12 +5215,17 @@ ira (FILE *f)
>
> ira_conflicts_p = optimize > 0;
>
> + /* Determine the number of pseudos actually requiring coloring. */
> + for (i = FIRST_PSEUDO_REGISTER; i < DF_REG_SIZE (df); i++)
> + num_used_regs += !!(DF_REG_USE_COUNT (i) + DF_REG_DEF_COUNT (i));
> +
> /* If there are too many pseudos and/or basic blocks (e.g. 10K
> pseudos and 10K blocks or 100K pseudos and 1K blocks), we will
> use simplified and faster algorithms in LRA. */
> lra_simple_p
> = (ira_use_lra_p
> - && max_reg_num () >= (1 << 26) / last_basic_block_for_fn (cfun));
> + && num_used_regs >= (1 << 26) / last_basic_block_for_fn (cfun));
> +
> if (lra_simple_p)
> {
> /* It permits to skip live range splitting in LRA. */
>
