Re: [PATCH] Fix instability of -fschedule-insn for x86

[Uros Bizjak <ubizjak at gmail dot com>]

Hello!

> This patch aims to fix all stability issues related to using the first
> scheduler in gcc
> for x86 target (there several reported issues related to this problem).
>
> Main idea of this activity is mostly to provide user a possibility to
> safely turn on first scheduler for his codes. In some cases this could
> positively affect performance, especially for in-order Atom.
>
> Below is short description of proposed changes.

> 2012-09-18  Yuri Rumyantsev  <ysrumyan@gmail.com>
>
>         * config/i386/i386.c (ix86_dep_by_shift_count_body) : Add
>         check on reload_completed since it can be invoked before
>         register allocation phase in 1st scheduler.
>         (ia32_multipass_dfa_lookahead) : Do not use dfa_lookahead for 1st
>         Scheduler to save compile time.
>         (ix86_sched_reorder) : Do not perform ready list reordering for 1st
>         Scheduler to save compile time.
>         (insn_is_function_arg) : New function. Returns true if lhs of insn is
>         HW function argument register.
>         (add_parameter_dependencies) : New function. Add output dependencies
>         for chain of function adjacent arguments if only there is a move to
>         likely spilled HW registers. Return first argument if at least one
>         dependence was added or NULL otherwise.
>         (avoid_func_arg_motion) : New function. Add output or anti dependency
>         from insn to first_arg to restrict code motion.
>         (add_dependee_for_func_arg) : New function. Avoid cross block motion of
>         function argument through adding dependency from the first non-jump
>         insn in bb.
>         (ix86_dependencies_evaluation_hook) : New function. Hook for schedule1:
>         avoid motion of function arguments passed in passed in likely spilled
>         HW registers.
>         (ix86_adjust_priority) : New function. Hook for schedule1: set priority
>         of moves from likely spilled HW registers to maximum to schedule them
>         as soon as possible.
>         (ix86_sched_init_global): Do not perform multipass scheduling for 1st
>         Scheduler to save compile time.

I would kindly ask scheduler expert to review the patch from the
scheduler functionality POV.

Thanks,
Uros.