dri/i965/brw_fs_reg_allocate.cpp

/*
 * Copyright © 2010 Intel Corporation
 *
 * 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.
 *
 * Authors:
 *    Eric Anholt <eric@anholt.net>
 *
 */

#include "brw_fs.h"
#include "glsl/glsl_types.h"
#include "glsl/ir_optimization.h"
#include "glsl/ir_print_visitor.h"

static void
assign_reg(int *reg_hw_locations, fs_reg *reg, int reg_width)
{
   if (reg->file == GRF) {
      assert(reg->reg_offset >= 0);
      reg->reg = reg_hw_locations[reg->reg] + reg->reg_offset * reg_width;
      reg->reg_offset = 0;
   }
}

void
fs_visitor::assign_regs_trivial()
{
   int hw_reg_mapping[this->virtual_grf_count + 1];
   int i;
   int reg_width = c->dispatch_width / 8;

   /* Note that compressed instructions require alignment to 2 registers. */
   hw_reg_mapping[0] = ALIGN(this->first_non_payload_grf, reg_width);
   for (i = 1; i <= this->virtual_grf_count; i++) {
      hw_reg_mapping[i] = (hw_reg_mapping[i - 1] +
			   this->virtual_grf_sizes[i - 1] * reg_width);
   }
   this->grf_used = hw_reg_mapping[this->virtual_grf_count];

   foreach_list(node, &this->instructions) {
      fs_inst *inst = (fs_inst *)node;

      assign_reg(hw_reg_mapping, &inst->dst, reg_width);
      assign_reg(hw_reg_mapping, &inst->src[0], reg_width);
      assign_reg(hw_reg_mapping, &inst->src[1], reg_width);
      assign_reg(hw_reg_mapping, &inst->src[2], reg_width);
   }

   if (this->grf_used >= max_grf) {
      fail("Ran out of regs on trivial allocator (%d/%d)\n",
	   this->grf_used, max_grf);
   }

}

static void
brw_alloc_reg_set_for_classes(struct brw_context *brw,
			      int *class_sizes,
			      int class_count,
			      int reg_width,
			      int base_reg_count)
{
   struct intel_context *intel = &brw->intel;

   /* Compute the total number of registers across all classes. */
   int ra_reg_count = 0;
   for (int i = 0; i < class_count; i++) {
      ra_reg_count += base_reg_count - (class_sizes[i] - 1);
   }

   ralloc_free(brw->wm.ra_reg_to_grf);
   brw->wm.ra_reg_to_grf = ralloc_array(brw, uint8_t, ra_reg_count);
   ralloc_free(brw->wm.regs);
   brw->wm.regs = ra_alloc_reg_set(brw, ra_reg_count);
   ralloc_free(brw->wm.classes);
   brw->wm.classes = ralloc_array(brw, int, class_count + 1);

   brw->wm.aligned_pairs_class = -1;

   /* Now, add the registers to their classes, and add the conflicts
    * between them and the base GRF registers (and also each other).
    */
   int reg = 0;
   int pairs_base_reg = 0;
   int pairs_reg_count = 0;
   for (int i = 0; i < class_count; i++) {
      int class_reg_count = base_reg_count - (class_sizes[i] - 1);
      brw->wm.classes[i] = ra_alloc_reg_class(brw->wm.regs);

      /* Save this off for the aligned pair class at the end. */
      if (class_sizes[i] == 2) {
	 pairs_base_reg = reg;
	 pairs_reg_count = class_reg_count;
      }

      for (int j = 0; j < class_reg_count; j++) {
	 ra_class_add_reg(brw->wm.regs, brw->wm.classes[i], reg);

	 brw->wm.ra_reg_to_grf[reg] = j;

	 for (int base_reg = j;
	      base_reg < j + class_sizes[i];
	      base_reg++) {
	    ra_add_transitive_reg_conflict(brw->wm.regs, base_reg, reg);
	 }

	 reg++;
      }
   }
   assert(reg == ra_reg_count);

   /* Add a special class for aligned pairs, which we'll put delta_x/y
    * in on gen5 so that we can do PLN.
    */
   if (brw->has_pln && reg_width == 1 && intel->gen < 6) {
      brw->wm.aligned_pairs_class = ra_alloc_reg_class(brw->wm.regs);

      for (int i = 0; i < pairs_reg_count; i++) {
	 if ((brw->wm.ra_reg_to_grf[pairs_base_reg + i] & 1) == 0) {
	    ra_class_add_reg(brw->wm.regs, brw->wm.aligned_pairs_class,
			     pairs_base_reg + i);
	 }
      }
      class_count++;
   }

   ra_set_finalize(brw->wm.regs);
}

bool
fs_visitor::assign_regs()
{
   /* Most of this allocation was written for a reg_width of 1
    * (dispatch_width == 8).  In extending to 16-wide, the code was
    * left in place and it was converted to have the hardware
    * registers it's allocating be contiguous physical pairs of regs
    * for reg_width == 2.
    */
   int reg_width = c->dispatch_width / 8;
   int hw_reg_mapping[this->virtual_grf_count];
   int first_assigned_grf = ALIGN(this->first_non_payload_grf, reg_width);
   int base_reg_count = (max_grf - first_assigned_grf) / reg_width;
   int class_sizes[base_reg_count];
   int class_count = 0;

   calculate_live_intervals();

   /* Set up the register classes.
    *
    * The base registers store a scalar value.  For texture samples,
    * we get virtual GRFs composed of 4 contiguous hw register.  For
    * structures and arrays, we store them as contiguous larger things
    * than that, though we should be able to do better most of the
    * time.
    */
   class_sizes[class_count++] = 1;
   if (brw->has_pln && intel->gen < 6) {
      /* Always set up the (unaligned) pairs for gen5, so we can find
       * them for making the aligned pair class.
       */
      class_sizes[class_count++] = 2;
   }
   for (int r = 0; r < this->virtual_grf_count; r++) {
      int i;

      for (i = 0; i < class_count; i++) {
	 if (class_sizes[i] == this->virtual_grf_sizes[r])
	    break;
      }
      if (i == class_count) {
	 if (this->virtual_grf_sizes[r] >= base_reg_count) {
	    fail("Object too large to register allocate.\n");
	 }

	 class_sizes[class_count++] = this->virtual_grf_sizes[r];
      }
   }

   brw_alloc_reg_set_for_classes(brw, class_sizes, class_count,
				 reg_width, base_reg_count);

   struct ra_graph *g = ra_alloc_interference_graph(brw->wm.regs,
						    this->virtual_grf_count);

   for (int i = 0; i < this->virtual_grf_count; i++) {
      for (int c = 0; c < class_count; c++) {
	 if (class_sizes[c] == this->virtual_grf_sizes[i]) {
            /* Special case: on pre-GEN6 hardware that supports PLN, the
             * second operand of a PLN instruction needs to be an
             * even-numbered register, so we have a special register class
             * wm_aligned_pairs_class to handle this case.  pre-GEN6 always
             * uses this->delta_x[BRW_WM_PERSPECTIVE_PIXEL_BARYCENTRIC] as the
             * second operand of a PLN instruction (since it doesn't support
             * any other interpolation modes).  So all we need to do is find
             * that register and set it to the appropriate class.
             */
	    if (brw->wm.aligned_pairs_class >= 0 &&
		this->delta_x[BRW_WM_PERSPECTIVE_PIXEL_BARYCENTRIC].reg == i) {
	       ra_set_node_class(g, i, brw->wm.aligned_pairs_class);
	    } else {
	       ra_set_node_class(g, i, brw->wm.classes[c]);
	    }
	    break;
	 }
      }

      for (int j = 0; j < i; j++) {
	 if (virtual_grf_interferes(i, j)) {
	    ra_add_node_interference(g, i, j);
	 }
      }
   }

   if (!ra_allocate_no_spills(g)) {
      /* Failed to allocate registers.  Spill a reg, and the caller will
       * loop back into here to try again.
       */
      int reg = choose_spill_reg(g);

      if (reg == -1) {
	 fail("no register to spill\n");
      } else if (c->dispatch_width == 16) {
	 fail("Failure to register allocate.  Reduce number of live scalar "
              "values to avoid this.");
      } else {
	 spill_reg(reg);
      }


      ralloc_free(g);

      return false;
   }

   /* Get the chosen virtual registers for each node, and map virtual
    * regs in the register classes back down to real hardware reg
    * numbers.
    */
   this->grf_used = first_assigned_grf;
   for (int i = 0; i < this->virtual_grf_count; i++) {
      int reg = ra_get_node_reg(g, i);

      hw_reg_mapping[i] = (first_assigned_grf +
			   brw->wm.ra_reg_to_grf[reg] * reg_width);
      this->grf_used = MAX2(this->grf_used,
			    hw_reg_mapping[i] + this->virtual_grf_sizes[i] *
			    reg_width);
   }

   foreach_list(node, &this->instructions) {
      fs_inst *inst = (fs_inst *)node;

      assign_reg(hw_reg_mapping, &inst->dst, reg_width);
      assign_reg(hw_reg_mapping, &inst->src[0], reg_width);
      assign_reg(hw_reg_mapping, &inst->src[1], reg_width);
      assign_reg(hw_reg_mapping, &inst->src[2], reg_width);
   }

   ralloc_free(g);

   return true;
}

void
fs_visitor::emit_unspill(fs_inst *inst, fs_reg dst, uint32_t spill_offset)
{
   fs_inst *unspill_inst = new(mem_ctx) fs_inst(FS_OPCODE_UNSPILL, dst);
   unspill_inst->offset = spill_offset;
   unspill_inst->ir = inst->ir;
   unspill_inst->annotation = inst->annotation;

   /* Choose a MRF that won't conflict with an MRF that's live across the
    * spill.  Nothing else will make it up to MRF 14/15.
    */
   unspill_inst->base_mrf = 14;
   unspill_inst->mlen = 1; /* header contains offset */
   inst->insert_before(unspill_inst);
}

int
fs_visitor::choose_spill_reg(struct ra_graph *g)
{
   float loop_scale = 1.0;
   float spill_costs[this->virtual_grf_count];
   bool no_spill[this->virtual_grf_count];

   for (int i = 0; i < this->virtual_grf_count; i++) {
      spill_costs[i] = 0.0;
      no_spill[i] = false;
   }

   /* Calculate costs for spilling nodes.  Call it a cost of 1 per
    * spill/unspill we'll have to do, and guess that the insides of
    * loops run 10 times.
    */
   foreach_list(node, &this->instructions) {
      fs_inst *inst = (fs_inst *)node;

      for (unsigned int i = 0; i < 3; i++) {
	 if (inst->src[i].file == GRF) {
	    spill_costs[inst->src[i].reg] += loop_scale;

            /* Register spilling logic assumes full-width registers; smeared
             * registers have a width of 1 so if we try to spill them we'll
             * generate invalid assembly.  This shouldn't be a problem because
             * smeared registers are only used as short-term temporaries when
             * loading pull constants, so spilling them is unlikely to reduce
             * register pressure anyhow.
             */
            if (inst->src[i].smear >= 0) {
               no_spill[inst->src[i].reg] = true;
            }
	 }
      }

      if (inst->dst.file == GRF) {
	 spill_costs[inst->dst.reg] += inst->regs_written() * loop_scale;

         if (inst->dst.smear >= 0) {
            no_spill[inst->dst.reg] = true;
         }
      }

      switch (inst->opcode) {

      case BRW_OPCODE_DO:
	 loop_scale *= 10;
	 break;

      case BRW_OPCODE_WHILE:
	 loop_scale /= 10;
	 break;

      case FS_OPCODE_SPILL:
	 if (inst->src[0].file == GRF)
	    no_spill[inst->src[0].reg] = true;
	 break;

      case FS_OPCODE_UNSPILL:
	 if (inst->dst.file == GRF)
	    no_spill[inst->dst.reg] = true;
	 break;

      default:
	 break;
      }
   }

   for (int i = 0; i < this->virtual_grf_count; i++) {
      if (!no_spill[i])
	 ra_set_node_spill_cost(g, i, spill_costs[i]);
   }

   return ra_get_best_spill_node(g);
}

void
fs_visitor::spill_reg(int spill_reg)
{
   int size = virtual_grf_sizes[spill_reg];
   unsigned int spill_offset = c->last_scratch;
   assert(ALIGN(spill_offset, 16) == spill_offset); /* oword read/write req. */
   c->last_scratch += size * REG_SIZE;

   /* Generate spill/unspill instructions for the objects being
    * spilled.  Right now, we spill or unspill the whole thing to a
    * virtual grf of the same size.  For most instructions, though, we
    * could just spill/unspill the GRF being accessed.
    */
   foreach_list(node, &this->instructions) {
      fs_inst *inst = (fs_inst *)node;

      for (unsigned int i = 0; i < 3; i++) {
	 if (inst->src[i].file == GRF &&
	     inst->src[i].reg == spill_reg) {
	    inst->src[i].reg = virtual_grf_alloc(1);
	    emit_unspill(inst, inst->src[i],
                         spill_offset + REG_SIZE * inst->src[i].reg_offset);
	 }
      }

      if (inst->dst.file == GRF &&
	  inst->dst.reg == spill_reg) {
         int subset_spill_offset = (spill_offset +
                                    REG_SIZE * inst->dst.reg_offset);
         inst->dst.reg = virtual_grf_alloc(inst->regs_written());
         inst->dst.reg_offset = 0;

	 /* If our write is going to affect just part of the
          * inst->regs_written(), then we need to unspill the destination
          * since we write back out all of the regs_written().
	  */
	 if (inst->predicated || inst->force_uncompressed || inst->force_sechalf) {
            fs_reg unspill_reg = inst->dst;
            for (int chan = 0; chan < inst->regs_written(); chan++) {
               emit_unspill(inst, unspill_reg,
                            subset_spill_offset + REG_SIZE * chan);
               unspill_reg.reg_offset++;
            }
	 }

	 fs_reg spill_src = inst->dst;
	 spill_src.reg_offset = 0;
	 spill_src.abs = false;
	 spill_src.negate = false;
	 spill_src.smear = -1;

	 for (int chan = 0; chan < inst->regs_written(); chan++) {
	    fs_inst *spill_inst = new(mem_ctx) fs_inst(FS_OPCODE_SPILL,
						       reg_null_f, spill_src);
	    spill_src.reg_offset++;
	    spill_inst->offset = subset_spill_offset + chan * REG_SIZE;
	    spill_inst->ir = inst->ir;
	    spill_inst->annotation = inst->annotation;
	    spill_inst->base_mrf = 14;
	    spill_inst->mlen = 2; /* header, value */
	    inst->insert_after(spill_inst);
	 }
      }
   }

   this->live_intervals_valid = false;
}