ir3_cp_postsched.c

/*
 * Copyright © 2020 Google, Inc.
 *
 * Permission is hereby granted, free of charge, to any person obtaining a
 * copy of this software and associated documentation files (the "Software"),
 * to deal in the Software without restriction, including without limitation
 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
 * and/or sell copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice (including the next
 * paragraph) shall be included in all copies or substantial portions of the
 * Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */

#include "util/ralloc.h"
#include "util/u_dynarray.h"

#include "ir3.h"

/**
 * A bit more extra cleanup after sched pass.  In particular, prior to
 * instruction scheduling, we can't easily eliminate unneeded mov's
 * from "arrays", because we don't yet know if there is an intervening
 * array-write scheduled before the use of the array-read.
 *
 * NOTE array is equivalent to nir "registers".. ie. it can be length of
 * one.  It is basically anything that is not SSA.
 */

/**
 * Check if any instruction before `use` and after `src` writes to the
 * specified array.  If `offset` is negative, it is a relative (a0.x)
 * access and we care about all writes to the array (as we don't know
 * which array element is read).  Otherwise in the case of non-relative
 * access, we only have to care about the write to the specified (>= 0)
 * offset. In this case, we update `def` to point to the last write in
 * between `use` and `src` to the same array, so that `use` points to
 * the correct array write.
 */
static bool
has_conflicting_write(struct ir3_instruction *src, struct ir3_instruction *use,
                      struct ir3_register **def, unsigned id, int offset)
{
   assert(src->block == use->block);
   bool last_write = true;

   /* NOTE that since src and use are in the same block, src by
    * definition appears in the block's instr_list before use:
    */
   foreach_instr_rev (instr, &use->node) {
      if (instr == src)
         break;

      /* if we are looking at a RELATIV read, we can't move
       * it past an a0.x write:
       */
      if ((offset < 0) && (dest_regs(instr) > 0) &&
          (instr->dsts[0]->num == regid(REG_A0, 0)))
         return true;

      if (!writes_gpr(instr))
         continue;

      struct ir3_register *dst = instr->dsts[0];
      if (!(dst->flags & IR3_REG_ARRAY))
         continue;

      if (dst->array.id != id)
         continue;

      /*
       * At this point, we have narrowed down an instruction
       * that writes to the same array.. check if it the write
       * is to an array element that we care about:
       */

      /* is write to an unknown array element? */
      if (dst->flags & IR3_REG_RELATIV)
         return true;

      /* is read from an unknown array element? */
      if (offset < 0)
         return true;

      /* is write to same array element? */
      if (dst->array.offset == offset)
         return true;

      if (last_write)
         *def = dst;

      last_write = false;
   }

   return false;
}

/* Can we fold the mov src into use without invalid flags? */
static bool
valid_flags(struct ir3_instruction *use, struct ir3_instruction *mov)
{
   struct ir3_register *src = mov->srcs[0];

   foreach_src_n (reg, n, use) {
      if (ssa(reg) != mov)
         continue;

      if (!ir3_valid_flags(use, n, reg->flags | src->flags))
         return false;
   }

   return true;
}

static bool
instr_cp_postsched(struct ir3_instruction *mov)
{
   struct ir3_register *src = mov->srcs[0];

   /* only consider mov's from "arrays", other cases we have
    * already considered already:
    */
   if (!(src->flags & IR3_REG_ARRAY))
      return false;

   int offset = (src->flags & IR3_REG_RELATIV) ? -1 : src->array.offset;

   /* Once we move the array read directly into the consuming
    * instruction(s), we will also need to update instructions
    * that had a false-dep on the original mov to have deps
    * on the consuming instructions:
    */
   struct util_dynarray newdeps;
   util_dynarray_init(&newdeps, mov->uses);

   foreach_ssa_use (use, mov) {
      if (use->block != mov->block)
         continue;

      if (is_meta(use))
         continue;

      struct ir3_register *def = src->def;
      if (has_conflicting_write(mov, use, &def, src->array.id, offset))
         continue;

      if (conflicts(mov->address, use->address))
         continue;

      if (!valid_flags(use, mov))
         continue;

      /* Ok, we've established that it is safe to remove this copy: */

      bool removed = false;
      foreach_src_n (reg, n, use) {
         if (ssa(reg) != mov)
            continue;

         use->srcs[n] = ir3_reg_clone(mov->block->shader, src);

         /* preserve (abs)/etc modifiers: */
         use->srcs[n]->flags |= reg->flags;

         /* If we're sinking the array read past any writes, make
          * sure to update it to point to the new previous write:
          */
         use->srcs[n]->def = def;

         removed = true;
      }

      /* the use could have been only a false-dep, only add to the newdeps
       * array and update the address if we've actually updated a real src
       * reg for the use:
       */
      if (removed) {
         if (src->flags & IR3_REG_RELATIV)
            ir3_instr_set_address(use, mov->address->def->instr);

         util_dynarray_append(&newdeps, struct ir3_instruction *, use);

         /* Remove the use from the src instruction: */
         _mesa_set_remove_key(mov->uses, use);
      }
   }

   /* Once we have the complete set of instruction(s) that are are now
    * directly reading from the array, update any false-dep uses to
    * now depend on these instructions.  The only remaining uses at
    * this point should be false-deps:
    */
   foreach_ssa_use (use, mov) {
      util_dynarray_foreach (&newdeps, struct ir3_instruction *, instrp) {
         struct ir3_instruction *newdep = *instrp;
         ir3_instr_add_dep(use, newdep);
      }
   }

   return util_dynarray_num_elements(&newdeps, struct ir3_instruction **) > 0;
}

bool
ir3_cp_postsched(struct ir3 *ir)
{
   void *mem_ctx = ralloc_context(NULL);
   bool progress = false;

   ir3_find_ssa_uses(ir, mem_ctx, false);

   foreach_block (block, &ir->block_list) {
      foreach_instr_safe (instr, &block->instr_list) {
         if (is_same_type_mov(instr))
            progress |= instr_cp_postsched(instr);
      }
   }

   ralloc_free(mem_ctx);

   return progress;
}