Re: [PATCH] On x86 allow if-conversion of more than one insn as long as there is at most one cmov (PR tree-optimization/79390)

[Uros Bizjak <ubizjak@gmail.com>]

On Sat, Apr 1, 2017 at 2:20 PM, Jakub Jelinek <jakub@redhat.com> wrote:
> Hi!
>
> As discussed in the PR, in the following testcase we don't if-convert
> with the generic (and many other) tuning, because we default to
> --param max-rtl-if-conversion-insns=1 in most of the tunings.
> The problem we have is with multiple cmov instructions, but in the
> testcase there is just one cmov and the other insn is turned into a SSE
> max insn, which is fine.
>
> This patch stops artificially lowering that param, and for one_if_conv_insn
> tuning it instead rejects the if-conversion if the resulting sequence has
> multiple cmov instructions.  The hook is passed if_info too, so it can
> in the future do better heuristics based on predictability of the edges,
> how far the uses of the cmov result are (I assume cmov major problem is
> latency, right?) etc.
>
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
>
> 2017-04-01  Jakub Jelinek  <jakub@redhat.com>
>
>         PR tree-optimization/79390
>         * target.h (struct noce_if_info): Declare.
>         * targhooks.h (default_noce_conversion_profitable_p): Declare.
>         * target.def (noce_conversion_profitable_p): New target hook.
>         * ifcvt.h (struct noce_if_info): New type, moved from ...
>         * ifcvt.c (struct noce_if_info): ... here.
>         (noce_conversion_profitable_p): Renamed to ...
>         (default_noce_conversion_profitable_p): ... this.  No longer
>         static nor inline.
>         (noce_try_store_flag_constants, noce_try_addcc,
>         noce_try_store_flag_mask, noce_try_cmove, noce_try_cmove_arith,
>         noce_convert_multiple_sets): Use targetm.noce_conversion_profitable_p
>         instead of noce_conversion_profitable_p.
>         * config/i386/i386.c: Include ifcvt.h.
>         (ix86_option_override_internal): Don't override
>         PARAM_MAX_RTL_IF_CONVERSION_INSNS default.
>         (ix86_noce_conversion_profitable_p): New function.
>         (TARGET_NOCE_CONVERSION_PROFITABLE_P): Redefine.
>         * config/i386/x86-tune.def (X86_TUNE_ONE_IF_CONV_INSN): Adjust comment.
>         * doc/tm.texi.in (TARGET_NOCE_CONVERSION_PROFITABLE_P): Add.
>         * doc/tm.texi: Regenerated.
>
>         * gcc.target/i386/pr79390.c: New test.
>         * gcc.dg/ifcvt-4.c: Use -mtune-ctrl=^one_if_conv_insn for i?86/x86_64.

x86 part LGTM.

Hopefully, this infrastructure will allow us to fix (or it already
fixes) PR 56309 [1].

[1] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=56309

Thanks,
Uros.