Re: [PATCH GCC][4/6]Support regional coalesce and live range computation

[Richard Biener <richard.guenther@gmail.com>]

On Thu, May 17, 2018 at 5:49 PM Bin.Cheng <amker.cheng@gmail.com> wrote:

> On Thu, May 17, 2018 at 3:04 PM, Richard Biener
> <richard.guenther@gmail.com> wrote:
> > On Tue, May 15, 2018 at 5:44 PM Bin.Cheng <amker.cheng@gmail.com> wrote:
> >
> >> On Fri, May 11, 2018 at 1:53 PM, Richard Biener
> >> <richard.guenther@gmail.com> wrote:
> >> > On Fri, May 4, 2018 at 6:23 PM, Bin Cheng <Bin.Cheng@arm.com> wrote:
> >> >> Hi,
> >> >> Following Jeff's suggestion, I am now using existing tree-ssa-live.c
> > and
> >> >> tree-ssa-coalesce.c to compute register pressure, rather than
inventing
> >> >> another live range solver.
> >> >>
> >> >> The major change is to record region's basic blocks in var_map and
use
> > that
> >> >> information in computation, rather than FOR_EACH_BB_FN.  For now
only
> > loop
> >> >> and function type regions are supported.  The default one is
function
> > type
> >> >> region which is used in out-of-ssa.  Loop type region will be used
in
> > next
> >> >> patch to compute information for a loop.
> >> >>
> >> >> Bootstrap and test on x86_64 and AArch64 ongoing.  Any comments?
> >> >
> >> > I believe your changes to create_outofssa_var_map should be done
> > differently
> >> > by simply only calling it from the coalescing context and passing in
the
> >> > var_map rather than initializing it therein and returning it.
> >> >
> >> > This also means the coalesce_vars_p flag in the var_map structure
looks
> >> > somewhat out-of-place.  That is, it looks you could do with many less
> >> > changes if you refactored what calls what slightly?  For example
> >> > the extra arg to gimple_can_coalesce_p looks unneeded.
> >> >
> >> > Just as a note I do have a CFG helper pending that computes RPO order
> >> > for SEME regions (attached).  loops are SEME regions, so your
RTYPE_SESE
> >> > is somewhat odd - I guess RTYPE_LOOP exists only because of the
> >> > convenience of passing in a loop * to the "constructor".  I'd rather
> >> > drop this region_type thing and always assume a SEME region - at
least
> >> > I didn't see anything in the patch that depends on any of the forms
> >> > apart from the initial BB gathering.
> >
> >> Hi Richard,
> >
> >> Thanks for reviewing.  I refactored tree-ssa-live.c and
> >> tree-ssa-coalesce.c following your comments.
> >> Basically I did following changes:
> >> 1) Remove region_type and only support loop region live range
computation.
> >>      Also I added one boolean field in var_map indicating whether we
> >> are computing
> >>      loop region live range or out-of-ssa.
> >> 2) Refactored create_outofssa_var_map into
> > create_coalesce_list_for_region and
> >>      populate_coalesce_list_for_outofssa.  Actually the original
> >> function name doesn't
> >>      quite make sense because it has nothing to do with var_map.
> >> 3) Hoist init_var_map up in call stack.  Now it's called by caller
> >> (out-of-ssa or live range)
> >>      and the returned var_map is passed to coalesce_* stuff.
> >> 4) Move global functions to tree-outof-ssa.c and make them static.
> >> 5) Save/restore flag_tree_coalesce_vars in order to avoid updating
> >> checks on the flag.
> >
> >> So how is this one?  Patch attached.
> >
> > A lot better.  Few things I noticed:
> >
> > +  map->bmp_bbs = BITMAP_ALLOC (NULL);
> >
> > use a bitmap_head member and bitmap_initialize ().
> >
> > +  map->vec_bbs = new vec<basic_block> ();
> >
> > use a vec<> member and map->vec_bbs = vNULL;
> >
> > Both changes remove an unnecessary indirection.
> >
> > +      map->outofssa_p = true;
> > +      basic_block bb;
> > +      FOR_EACH_BB_FN (bb, cfun)
> > +       {
> > +         bitmap_set_bit (map->bmp_bbs, bb->index);
> > +         map->vec_bbs->safe_push (bb);
> > +       }
> >
> > I think you can avoid populating the bitmap and return
> > true unconditionally for outofssa_p in the contains function?
> > Ah, you already do - so why populate the bitmap?
> >
> > +/* Return TRUE if region of the MAP contains basic block BB.  */
> > +
> > +inline bool
> > +region_contains_p (var_map map, basic_block bb)
> > +{
> > +  if (bb == ENTRY_BLOCK_PTR_FOR_FN (cfun)
> > +      || bb == EXIT_BLOCK_PTR_FOR_FN (cfun))
> > +    return false;
> > +
> > +  if (map->outofssa_p)
> > +    return true;
> > +
> > +  return bitmap_bit_p (map->bmp_bbs, bb->index);
> >
> > the entry/exit block check should be conditional in map->outofssa_p
> > but I think we should never get the function called with those args
> > so we can as well use a gcc_checking_assert ()?
> >
> > I think as followup we should try to get a BB order that
> > is more suited for the dataflow problem.  Btw, I was
> > thinking about adding anoter "visited" BB flag that is guaranteed to
> > be unset and free to be used by infrastructure.  So the bitmap
> > could be elided for a bb flag check (but we need to clear that flag
> > at the end of processing).  Not sure if it's worth to add a machinery
> > to dynamically assign pass-specific flags...  it would at least be
> > less error prone.  Sth to think about.
> >
> > So -- I think the patch is ok with the two indirections removed,
> > the rest can be optimized as followup.
> Hi,
> This is the updated patch.  I moved checks on ENTRY/EXIT blocks under
> outofssa_p,
> as well as changed vec_bbs into object.  Note bmp_bbs is kept in
> pointer so that we
> can avoid allocating memory in out-of-ssa case.
> Bootstrap and test ongoing.  Is it OK?

Yes.
Thanks,
Richard.

> Thanks,
> bin
> >
> > Thanks,
> > Richard.
> >
> >
> >> Thanks,
> >> bin
> >> 2018-05-15  Bin Cheng  <bin.cheng@arm.com>
> >
> >>      * tree-outof-ssa.c (tree-ssa.h, tree-dfa.h): Include header files.
> >>      (create_default_def, for_all_parms): Moved from
tree-ssa-coalesce.c.
> >>      (parm_default_def_partition_arg): Ditto.
> >>      (set_parm_default_def_partition): Ditto.
> >>      (get_parm_default_def_partitions): Ditto and make it static.
> >>      (get_undefined_value_partitions): Ditto and make it static.
> >>      (remove_ssa_form): Refactor call to init_var_map here.
> >>      * tree-ssa-coalesce.c (build_ssa_conflict_graph): Support live
range
> >>      computation for loop region.
> >>      (coalesce_partitions, compute_optimized_partition_bases): Ditto.
> >>      (register_default_def): Delete.
> >>      (for_all_parms, create_default_def): Move to tree-outof-ssa.c.
> >>      (parm_default_def_partition_arg): Ditto.
> >>      (set_parm_default_def_partition): Ditto.
> >>      (get_parm_default_def_partitions): Ditto and make it static.
> >>      (get_undefined_value_partitions): Ditto and make it static.
> >>      (coalesce_with_default, coalesce_with_default): Update comment.
> >>      (create_coalesce_list_for_region): New func factored out from
> >>      create_outofssa_var_map.
> >>      (populate_coalesce_list_for_outofssa): New func factored out from
> >>      create_outofssa_var_map and coalesce_ssa_name.
> >>      (create_outofssa_var_map): Delete.
> >>      (coalesce_ssa_name): Refactor to support live range computation.
> >>      * tree-ssa-coalesce.h (coalesce_ssa_name): Change decl.
> >>      (get_parm_default_def_partitions): Delete.
> >>      (get_undefined_value_partitions): Ditto.
> >>      * tree-ssa-live.c (init_var_map, delete_var_map): Support live
range
> >>      computation for loop region.
> >>      (new_tree_live_info, loe_visit_block): Ditto.
> >>      (live_worklist, set_var_live_on_entry): Ditto.
> >>      (calculate_live_on_exit, verify_live_on_entry): Ditto.
> >>      * tree-ssa-live.h (struct _var_map): New fields.
> >>      (init_var_map): Change decl.
> >>      (region_contains_p): New.