Re: [sel-sched] Shrink memory consumption on extra large basic blocks

[Vladimir Makarov <vmakarov at redhat dot com>]

Andrey Belevantsev wrote:
> Hi,
>
> Steve kindly pointed out to me that on ia64 gcc needs a lot of memory 
> when compiling limits-fnargs.c with -O3.  The reason for this is that 
> we have a basic block with ~150K instructions, and in selective 
> scheduler one of the ideas for speeding it up was to cache the effects 
> of an insn inside the dependence context created solely for this 
> insn.  A dependence context has the reg_last array that holds 
> information for each register.  It is not a problem with usual regions 
> (at most several hundred insns), but for a region with ~130K insns and 
> on ia64 with >300 hard registers we need something like 12Kb per insn, 
> which totals around 1.5Gb.
>
> Fortunately, there is an easy way out  -- when not pipelining (and we 
> never pipeline such supersize regions), we only need this information 
> for insns that are in our lookahead window, as we'd never move 
> anything through scheduled insns.   Thus, lazy allocating reg_last 
> array and freeing it after just scheduling an insn does the trick.
>
> The patch (also with extending per-insn data vector by smaller chunks) 
> lets me compile the test under 600Mb.  I haven't found other easy 
> candidates for optimizing memory footprints.  Bundling allocates quite 
> a lot for storing bundle states for each insn, but no obvious way to 
> shrink them.
>
> Bootstrapped and tested on ia64 with selective scheduling enabled at 
> -O2, regular bootstrap is in progress.  Ok for trunk if it succeeds?
Ok. Thanks, Andrey.
> 2009-11-12  Andrey Belevantsev  <abel@ispras.ru>
>
>     * sched-deps.c (init_deps): New parameter lazy_reg_last.  Don't
>     allocate reg_last when in case lazy_reg_last is true.
>     (init_deps_reg_last): New.
>     (free_deps): When max_reg is 0, this context is already freed.
>     * sched-int.h (init_deps_reg_last): Export.
>     (init_deps): Update prototype.
>     * sched-ebb.c (schedule_ebb): Update the call to init_deps.
>     * sched-rgn.c (sched_rgn_compute_dependencies): Likewise.
>     * ddg.c (build_intra_loop_deps): Likewise.
>     * sel-sched-ir.c (copy_deps_context, create_deps_context,
>     reset_deps_context, deps_init_id): Likewise.
>     (init_first_time_insn_data): Lazy allocate INSN_DEPS_CONTEXT.
>     (free_data_for_scheduled_insn): New, break down from ...
>     (free_first_time_insn_data): ... here.
>     (has_dependence_p): Allocate reg_last now, when it is needed.
>     * sel-sched-ir.h (free_data_for_scheduled_insn): Export.
>     * sel-sched.c (update_seqnos_and_stage): Free INSN_DEPS_CONTEXT
>     in scheduled insn.