[PATCH 1/4] openacc: Middle-end worker-partitioning support

Thomas Schwinge thomas@codesourcery.com
Wed Aug 4 13:56:49 GMT 2021


On 2021-03-02T04:20:11-0800, Julian Brown <julian@codesourcery.com> wrote:
> This patch implements worker-partitioning support in the middle end,
> by rewriting gimple.  [...]


> This version of the patch [...]
> avoids moving SESE-region finding code out
> of the NVPTX backend

So that's 'struct bb_sese' and following functions.

> since that code isn't used by the middle-end worker
> partitioning neutering/broadcasting implementation yet.

I understand correctly that "isn't used [...] yet" means that (a) "this
isn't implemented yet" (on og11 etc.), and doesn't mean (b) "is missing
from this patch submission"?  ... thus from (a) it follows that we may
later also drop from the og11 branch these changes?

Relatedly, a nontrivial amount of data structures/logic/code did get
duplicated from the nvptx back end, and modified slightly or
not-so-slightly (RTL vs. GIMPLE plus certain implementation "details").

We should at least cross reference the two instances, to make sure that
any changes to one are also propagated to the other.  (I'll take care.)

And then, do you (or anyone else, of course) happen to have any clever
idea about how to avoid the duplication, and somehow combine the RTL
vs. GIMPLE implementations?  Given that we nowadays may use C++ -- do you
foresee it feasible to have an abstract base class capturing basically
the data structures, logic, common code, and then RTL-specialized plus
GIMPLE-specialized classes inheriting from that?

For example:

    $ sed -e s%parallel_g%parallel%g < gcc/oacc-neuter-bcast.c > gcc/oacc-neuter-bcast.c_
    $ git diff --no-index --word-diff -b --patience gcc/config/nvptx/nvptx.c gcc/oacc-neuter-bcast.c_
    /* Loop structure of the function.  The entire function is described as
       a NULL loop.  */
    @@ -3229,17 +80,21 @@ struct parallel
      basic_block forked_block;
      basic_block join_block;

      [-rtx_insn *forked_insn;-]
    [-  rtx_insn *join_insn;-]{+gimple *forked_stmt;+}
    {+  gimple *join_stmt;+}

      [-rtx_insn *fork_insn;-]
    [-  rtx_insn *joining_insn;-]{+gimple *fork_stmt;+}
    {+  gimple *joining_stmt;+}

      /* Basic blocks in this parallel, but not in child parallels.  The
         FORKED and JOINING blocks are in the partition.  The FORK and JOIN
         blocks are not.  */
      auto_vec<basic_block> blocks;

      {+tree record_type;+}
    {+  tree sender_decl;+}
    {+  tree receiver_decl;+}

      parallel (parallel *parent, unsigned mode);
      ~parallel ();
    @@ -3252,8 +107,12 @@ parallel::parallel (parallel *parent_, unsigned mask_)
      :parent (parent_), next (0), inner (0), mask (mask_), inner_mask (0)
      forked_block = join_block = 0;
      [-forked_insn-]{+forked_stmt+} = [-join_insn-]{+join_stmt+} = [-0;-]
    [-  fork_insn-]{+NULL;+}
    {+  fork_stmt+} = [-joining_insn-]{+joining_stmt+} = [-0;-]{+NULL;+}

    {+  record_type = NULL_TREE;+}
    {+  sender_decl = NULL_TREE;+}
    {+  receiver_decl = NULL_TREE;+}

      if (parent)
    @@ -3268,12 +127,54 @@ parallel::~parallel ()
      delete next;
    /* Split basic blocks such that each forked and join unspecs are at
       the start of their basic blocks.  Thus afterwards each block will
    @@ -3284,111 +185,168 @@ typedef auto_vec<insn_bb_t> insn_bb_vec_t;
       used when finding partitions.  */

    static void
    [-nvptx_split_blocks (bb_insn_map_t-]{+omp_sese_split_blocks (bb_stmt_map_t+} *map)
      [-insn_bb_vec_t-]{+auto_vec<gimple *>+} worklist;
      basic_block block;
    [-  rtx_insn *insn;-]

      /* Locate all the reorg instructions of interest.  */
      FOR_ALL_BB_FN (block, cfun)
    [-      bool seen_insn = false;-]

          /* Clear visited flag, for use by parallel locator  */
          block->flags &= ~BB_VISITED;

          [-FOR_BB_INSNS (block, insn)-]{+for (gimple_stmt_iterator gsi = gsi_start_bb (block);+}
    {+     !gsi_end_p (gsi);+}
    {+     gsi_next (&gsi))+}
    /* Dump this parallel and all its inner parallels.  */

    static void
    [-nvptx_dump_pars-]{+omp_sese_dump_pars+} (parallel *par, unsigned depth)
      fprintf (dump_file, "%u: mask %d {+(%s)+} head=%d, tail=%d\n",
           depth, par->mask, {+mask_name (par->mask),+}
           par->forked_block ? par->forked_block->index : -1,
           par->join_block ? par->join_block->index : -1);

    @@ -3399,10 +357,10 @@ nvptx_dump_pars (parallel *par, unsigned depth)
        fprintf (dump_file, " %d", block->index);
      fprintf (dump_file, "\n");
      if (par->inner)
        [-nvptx_dump_pars-]{+omp_sese_dump_pars+} (par->inner, depth + 1);

      if (par->next)
        [-nvptx_dump_pars-]{+omp_sese_dump_pars+} (par->next, depth);

    /* If BLOCK contains a fork/join marker, process it to create or
    @@ -3410,60 +368,84 @@ nvptx_dump_pars (parallel *par, unsigned depth)
       and then walk successor blocks.   */

    static parallel *
    [-nvptx_find_par (bb_insn_map_t-]{+omp_sese_find_par (bb_stmt_map_t+} *map, parallel *par, basic_block block)
      if (block->flags & BB_VISITED)
        return par;
      block->flags |= BB_VISITED;

      if [-(rtx_insn **endp-]{+(gimple **stmtp+} = map->get (block))
    static parallel *
    [-nvptx_discover_pars (bb_insn_map_t-]{+omp_sese_discover_pars (bb_stmt_map_t+} *map)
      basic_block block;

    @@ -3502,3468 +485,1033 @@ nvptx_discover_pars (bb_insn_map_t *map)
      block = ENTRY_BLOCK_PTR_FOR_FN (cfun);
      block->flags &= ~BB_VISITED;

      parallel *par = [-nvptx_find_par-]{+omp_sese_find_par+} (map, 0, block);

      if (dump_file)
          fprintf (dump_file, "\nLoops\n");
          [-nvptx_dump_pars-]{+omp_sese_dump_pars+} (par, 0);
          fprintf (dump_file, "\n");

      return par;

(For brevity, I stripped out the parts where implementation "details"
differ considerably.)

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