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

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

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.

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.