i965: Note that write-after-write dependencies are blocking.

[mesa.git] / src / mesa / drivers / dri / i965 / brw_fs_schedule_instructions.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"

/** @file brw_fs_schedule_instructions.cpp
 *
 * List scheduling of FS instructions.
 *
 * The basic model of the list scheduler is to take a basic block,
 * compute a DAG of the dependencies (RAW ordering with latency, WAW
 * ordering with latency, WAR ordering), and make a list of the DAG heads.
 * Heuristically pick a DAG head, then put all the children that are
 * now DAG heads into the list of things to schedule.
 *
 * The heuristic is the important part.  We're trying to be cheap,
 * since actually computing the optimal scheduling is NP complete.
 * What we do is track a "current clock".  When we schedule a node, we
 * update the earliest-unblocked clock time of its children, and
 * increment the clock.  Then, when trying to schedule, we just pick
 * the earliest-unblocked instruction to schedule.
 *
 * Note that often there will be many things which could execute
 * immediately, and there are a range of heuristic options to choose
 * from in picking among those.
 */

static bool debug = false;

class schedule_node : public exec_node
{
public:
   schedule_node(fs_inst *inst, int gen)
   {
      this->inst = inst;
      this->child_array_size = 0;
      this->children = NULL;
      this->child_latency = NULL;
      this->child_count = 0;
      this->parent_count = 0;
      this->unblocked_time = 0;

      if (gen >= 7)
         set_latency_gen7();
      else
         set_latency_gen4();
   }

   void set_latency_gen4();
   void set_latency_gen7();

   fs_inst *inst;
   schedule_node **children;
   int *child_latency;
   int child_count;
   int parent_count;
   int child_array_size;
   int unblocked_time;
   int latency;
};

void
schedule_node::set_latency_gen4()
{
   int chans = 8;
   int math_latency = 22;

   switch (inst->opcode) {
   case SHADER_OPCODE_RCP:
      this->latency = 1 * chans * math_latency;
      break;
   case SHADER_OPCODE_RSQ:
      this->latency = 2 * chans * math_latency;
      break;
   case SHADER_OPCODE_INT_QUOTIENT:
   case SHADER_OPCODE_SQRT:
   case SHADER_OPCODE_LOG2:
      /* full precision log.  partial is 2. */
      this->latency = 3 * chans * math_latency;
      break;
   case SHADER_OPCODE_INT_REMAINDER:
   case SHADER_OPCODE_EXP2:
      /* full precision.  partial is 3, same throughput. */
      this->latency = 4 * chans * math_latency;
      break;
   case SHADER_OPCODE_POW:
      this->latency = 8 * chans * math_latency;
      break;
   case SHADER_OPCODE_SIN:
   case SHADER_OPCODE_COS:
      /* minimum latency, max is 12 rounds. */
      this->latency = 5 * chans * math_latency;
      break;
   default:
      this->latency = 2;
      break;
   }
}

void
schedule_node::set_latency_gen7()
{
   switch (inst->opcode) {
   case BRW_OPCODE_MAD:
      /* 3 cycles (this is said to be 4 cycles sometimes depending on the
       * register numbers in the sources):
       * mad(8) g4<1>F g2.2<4,1,1>F.x  g2<4,1,1>F.x g2.1<4,1,1>F.x { align16 WE_normal 1Q };
       *
       * 20 cycles:
       * mad(8) g4<1>F g2.2<4,1,1>F.x  g2<4,1,1>F.x g2.1<4,1,1>F.x { align16 WE_normal 1Q };
       * mov(8) null   g4<4,4,1>F                     { align16 WE_normal 1Q };
       */
      latency = 17;
      break;

   case SHADER_OPCODE_RCP:
   case SHADER_OPCODE_RSQ:
   case SHADER_OPCODE_SQRT:
   case SHADER_OPCODE_LOG2:
   case SHADER_OPCODE_EXP2:
   case SHADER_OPCODE_SIN:
   case SHADER_OPCODE_COS:
      /* 2 cycles:
       * math inv(8) g4<1>F g2<0,1,0>F      null       { align1 WE_normal 1Q };
       *
       * 18 cycles:
       * math inv(8) g4<1>F g2<0,1,0>F      null       { align1 WE_normal 1Q };
       * mov(8)      null   g4<8,8,1>F                 { align1 WE_normal 1Q };
       *
       * Same for exp2, log2, rsq, sqrt, sin, cos.
       */
      latency = 16;
      break;

   case SHADER_OPCODE_POW:
      /* 2 cycles:
       * math pow(8) g4<1>F g2<0,1,0>F   g2.1<0,1,0>F  { align1 WE_normal 1Q };
       *
       * 26 cycles:
       * math pow(8) g4<1>F g2<0,1,0>F   g2.1<0,1,0>F  { align1 WE_normal 1Q };
       * mov(8)      null   g4<8,8,1>F                 { align1 WE_normal 1Q };
       */
      latency = 24;
      break;

   case SHADER_OPCODE_TEX:
   case SHADER_OPCODE_TXD:
   case SHADER_OPCODE_TXF:
   case SHADER_OPCODE_TXL:
      /* 18 cycles:
       * mov(8)  g115<1>F   0F                         { align1 WE_normal 1Q };
       * mov(8)  g114<1>F   0F                         { align1 WE_normal 1Q };
       * send(8) g4<1>UW    g114<8,8,1>F
       *   sampler (10, 0, 0, 1) mlen 2 rlen 4         { align1 WE_normal 1Q };
       *
       * 697 +/-49 cycles (min 610, n=26):
       * mov(8)  g115<1>F   0F                         { align1 WE_normal 1Q };
       * mov(8)  g114<1>F   0F                         { align1 WE_normal 1Q };
       * send(8) g4<1>UW    g114<8,8,1>F
       *   sampler (10, 0, 0, 1) mlen 2 rlen 4         { align1 WE_normal 1Q };
       * mov(8)  null       g4<8,8,1>F                 { align1 WE_normal 1Q };
       *
       * So the latency on our first texture load of the batchbuffer takes
       * ~700 cycles, since the caches are cold at that point.
       *
       * 840 +/- 92 cycles (min 720, n=25):
       * mov(8)  g115<1>F   0F                         { align1 WE_normal 1Q };
       * mov(8)  g114<1>F   0F                         { align1 WE_normal 1Q };
       * send(8) g4<1>UW    g114<8,8,1>F
       *   sampler (10, 0, 0, 1) mlen 2 rlen 4         { align1 WE_normal 1Q };
       * mov(8)  null       g4<8,8,1>F                 { align1 WE_normal 1Q };
       * send(8) g4<1>UW    g114<8,8,1>F
       *   sampler (10, 0, 0, 1) mlen 2 rlen 4         { align1 WE_normal 1Q };
       * mov(8)  null       g4<8,8,1>F                 { align1 WE_normal 1Q };
       *
       * On the second load, it takes just an extra ~140 cycles, and after
       * accounting for the 14 cycles of the MOV's latency, that makes ~130.
       *
       * 683 +/- 49 cycles (min = 602, n=47):
       * mov(8)  g115<1>F   0F                         { align1 WE_normal 1Q };
       * mov(8)  g114<1>F   0F                         { align1 WE_normal 1Q };
       * send(8) g4<1>UW    g114<8,8,1>F
       *   sampler (10, 0, 0, 1) mlen 2 rlen 4         { align1 WE_normal 1Q };
       * send(8) g50<1>UW   g114<8,8,1>F
       *   sampler (10, 0, 0, 1) mlen 2 rlen 4         { align1 WE_normal 1Q };
       * mov(8)  null       g4<8,8,1>F                 { align1 WE_normal 1Q };
       *
       * The unit appears to be pipelined, since this matches up with the
       * cache-cold case, despite there being two loads here.  If you replace
       * the g4 in the MOV to null with g50, it's still 693 +/- 52 (n=39).
       *
       * So, take some number between the cache-hot 140 cycles and the
       * cache-cold 700 cycles.  No particular tuning was done on this.
       *
       * I haven't done significant testing of the non-TEX opcodes.  TXL at
       * least looked about the same as TEX.
       */
      latency = 200;
      break;

   case SHADER_OPCODE_TXS:
      /* Testing textureSize(sampler2D, 0), one load was 420 +/- 41
       * cycles (n=15):
       * mov(8)   g114<1>UD  0D                        { align1 WE_normal 1Q };
       * send(8)  g6<1>UW    g114<8,8,1>F
       *   sampler (10, 0, 10, 1) mlen 1 rlen 4        { align1 WE_normal 1Q };
       * mov(16)  g6<1>F     g6<8,8,1>D                { align1 WE_normal 1Q };
       *
       *
       * Two loads was 535 +/- 30 cycles (n=19):
       * mov(16)   g114<1>UD  0D                       { align1 WE_normal 1H };
       * send(16)  g6<1>UW    g114<8,8,1>F
       *   sampler (10, 0, 10, 2) mlen 2 rlen 8        { align1 WE_normal 1H };
       * mov(16)   g114<1>UD  0D                       { align1 WE_normal 1H };
       * mov(16)   g6<1>F     g6<8,8,1>D               { align1 WE_normal 1H };
       * send(16)  g8<1>UW    g114<8,8,1>F
       *   sampler (10, 0, 10, 2) mlen 2 rlen 8        { align1 WE_normal 1H };
       * mov(16)   g8<1>F     g8<8,8,1>D               { align1 WE_normal 1H };
       * add(16)   g6<1>F     g6<8,8,1>F   g8<8,8,1>F  { align1 WE_normal 1H };
       *
       * Since the only caches that should matter are just the
       * instruction/state cache containing the surface state, assume that we
       * always have hot caches.
       */
      latency = 100;
      break;

   case FS_OPCODE_VARYING_PULL_CONSTANT_LOAD:
   case FS_OPCODE_UNIFORM_PULL_CONSTANT_LOAD:
      /* testing using varying-index pull constants:
       *
       * 16 cycles:
       * mov(8)  g4<1>D  g2.1<0,1,0>F                  { align1 WE_normal 1Q };
       * send(8) g4<1>F  g4<8,8,1>D
       *   data (9, 2, 3) mlen 1 rlen 1                { align1 WE_normal 1Q };
       *
       * ~480 cycles:
       * mov(8)  g4<1>D  g2.1<0,1,0>F                  { align1 WE_normal 1Q };
       * send(8) g4<1>F  g4<8,8,1>D
       *   data (9, 2, 3) mlen 1 rlen 1                { align1 WE_normal 1Q };
       * mov(8)  null    g4<8,8,1>F                    { align1 WE_normal 1Q };
       *
       * ~620 cycles:
       * mov(8)  g4<1>D  g2.1<0,1,0>F                  { align1 WE_normal 1Q };
       * send(8) g4<1>F  g4<8,8,1>D
       *   data (9, 2, 3) mlen 1 rlen 1                { align1 WE_normal 1Q };
       * mov(8)  null    g4<8,8,1>F                    { align1 WE_normal 1Q };
       * send(8) g4<1>F  g4<8,8,1>D
       *   data (9, 2, 3) mlen 1 rlen 1                { align1 WE_normal 1Q };
       * mov(8)  null    g4<8,8,1>F                    { align1 WE_normal 1Q };
       *
       * So, if it's cache-hot, it's about 140.  If it's cache cold, it's
       * about 460.  We expect to mostly be cache hot, so pick something more
       * in that direction.
       */
      latency = 200;
      break;

   default:
      /* 2 cycles:
       * mul(8) g4<1>F g2<0,1,0>F      0.5F            { align1 WE_normal 1Q };
       *
       * 16 cycles:
       * mul(8) g4<1>F g2<0,1,0>F      0.5F            { align1 WE_normal 1Q };
       * mov(8) null   g4<8,8,1>F                      { align1 WE_normal 1Q };
       */
      latency = 14;
      break;
   }
}

class instruction_scheduler {
public:
   instruction_scheduler(fs_visitor *v, void *mem_ctx, int grf_count,
                         bool post_reg_alloc)
   {
      this->v = v;
      this->mem_ctx = ralloc_context(mem_ctx);
      this->grf_count = grf_count;
      this->instructions.make_empty();
      this->instructions_to_schedule = 0;
      this->post_reg_alloc = post_reg_alloc;
   }

   ~instruction_scheduler()
   {
      ralloc_free(this->mem_ctx);
   }
   void add_barrier_deps(schedule_node *n);
   void add_dep(schedule_node *before, schedule_node *after, int latency);
   void add_dep(schedule_node *before, schedule_node *after);

   void add_inst(fs_inst *inst);
   void calculate_deps();
   void schedule_instructions(fs_inst *next_block_header);

   bool is_compressed(fs_inst *inst);

   void *mem_ctx;

   bool post_reg_alloc;
   int instructions_to_schedule;
   int grf_count;
   exec_list instructions;
   fs_visitor *v;
};

void
instruction_scheduler::add_inst(fs_inst *inst)
{
   schedule_node *n = new(mem_ctx) schedule_node(inst, v->intel->gen);

   assert(!inst->is_head_sentinel());
   assert(!inst->is_tail_sentinel());

   this->instructions_to_schedule++;

   inst->remove();
   instructions.push_tail(n);
}

/**
 * Add a dependency between two instruction nodes.
 *
 * The @after node will be scheduled after @before.  We will try to
 * schedule it @latency cycles after @before, but no guarantees there.
 */
void
instruction_scheduler::add_dep(schedule_node *before, schedule_node *after,
                               int latency)
{
   if (!before || !after)
      return;

   assert(before != after);

   for (int i = 0; i < before->child_count; i++) {
      if (before->children[i] == after) {
         before->child_latency[i] = MAX2(before->child_latency[i], latency);
         return;
      }
   }

   if (before->child_array_size <= before->child_count) {
      if (before->child_array_size < 16)
         before->child_array_size = 16;
      else
         before->child_array_size *= 2;

      before->children = reralloc(mem_ctx, before->children,
                                  schedule_node *,
                                  before->child_array_size);
      before->child_latency = reralloc(mem_ctx, before->child_latency,
                                       int, before->child_array_size);
   }

   before->children[before->child_count] = after;
   before->child_latency[before->child_count] = latency;
   before->child_count++;
   after->parent_count++;
}

void
instruction_scheduler::add_dep(schedule_node *before, schedule_node *after)
{
   if (!before)
      return;

   add_dep(before, after, before->latency);
}

/**
 * Sometimes we really want this node to execute after everything that
 * was before it and before everything that followed it.  This adds
 * the deps to do so.
 */
void
instruction_scheduler::add_barrier_deps(schedule_node *n)
{
   schedule_node *prev = (schedule_node *)n->prev;
   schedule_node *next = (schedule_node *)n->next;

   if (prev) {
      while (!prev->is_head_sentinel()) {
         add_dep(prev, n, 0);
         prev = (schedule_node *)prev->prev;
      }
   }

   if (next) {
      while (!next->is_tail_sentinel()) {
         add_dep(n, next, 0);
         next = (schedule_node *)next->next;
      }
   }
}

/* instruction scheduling needs to be aware of when an MRF write
 * actually writes 2 MRFs.
 */
bool
instruction_scheduler::is_compressed(fs_inst *inst)
{
   return (v->dispatch_width == 16 &&
           !inst->force_uncompressed &&
           !inst->force_sechalf);
}

void
instruction_scheduler::calculate_deps()
{
   /* Pre-register-allocation, this tracks the last write per VGRF (so
    * different reg_offsets within it can interfere when they shouldn't).
    * After register allocation, reg_offsets are gone and we track individual
    * GRF registers.
    */
   schedule_node *last_grf_write[grf_count];
   schedule_node *last_mrf_write[BRW_MAX_MRF];
   schedule_node *last_conditional_mod[2] = { NULL, NULL };
   /* Fixed HW registers are assumed to be separate from the virtual
    * GRFs, so they can be tracked separately.  We don't really write
    * to fixed GRFs much, so don't bother tracking them on a more
    * granular level.
    */
   schedule_node *last_fixed_grf_write = NULL;
   int reg_width = v->dispatch_width / 8;

   /* The last instruction always needs to still be the last
    * instruction.  Either it's flow control (IF, ELSE, ENDIF, DO,
    * WHILE) and scheduling other things after it would disturb the
    * basic block, or it's FB_WRITE and we should do a better job at
    * dead code elimination anyway.
    */
   schedule_node *last = (schedule_node *)instructions.get_tail();
   add_barrier_deps(last);

   memset(last_grf_write, 0, sizeof(last_grf_write));
   memset(last_mrf_write, 0, sizeof(last_mrf_write));

   /* top-to-bottom dependencies: RAW and WAW. */
   foreach_list(node, &instructions) {
      schedule_node *n = (schedule_node *)node;
      fs_inst *inst = n->inst;

      /* read-after-write deps. */
      for (int i = 0; i < 3; i++) {
         if (inst->src[i].file == GRF) {
            if (post_reg_alloc) {
               for (int r = 0; r < reg_width; r++)
                  add_dep(last_grf_write[inst->src[i].reg + r], n);
            } else {
               add_dep(last_grf_write[inst->src[i].reg], n);
            }
         } else if (inst->src[i].file == FIXED_HW_REG &&
                    (inst->src[i].fixed_hw_reg.file ==
                     BRW_GENERAL_REGISTER_FILE)) {
            if (post_reg_alloc) {
               for (int r = 0; r < reg_width; r++)
                  add_dep(last_grf_write[inst->src[i].fixed_hw_reg.nr + r], n);
            } else {
               add_dep(last_fixed_grf_write, n);
            }
         } else if (inst->src[i].file != BAD_FILE &&
                    inst->src[i].file != IMM &&
                    inst->src[i].file != UNIFORM) {
            assert(inst->src[i].file != MRF);
            add_barrier_deps(n);
         }
      }

      for (int i = 0; i < inst->mlen; i++) {
         /* It looks like the MRF regs are released in the send
          * instruction once it's sent, not when the result comes
          * back.
          */
         add_dep(last_mrf_write[inst->base_mrf + i], n);
      }

      if (inst->predicate) {
         add_dep(last_conditional_mod[inst->flag_subreg], n);
      }

      /* write-after-write deps. */
      if (inst->dst.file == GRF) {
         if (post_reg_alloc) {
            for (int r = 0; r < inst->regs_written() * reg_width; r++) {
               add_dep(last_grf_write[inst->dst.reg + r], n);
               last_grf_write[inst->dst.reg + r] = n;
            }
         } else {
            add_dep(last_grf_write[inst->dst.reg], n);
            last_grf_write[inst->dst.reg] = n;
         }
      } else if (inst->dst.file == MRF) {
         int reg = inst->dst.reg & ~BRW_MRF_COMPR4;

         add_dep(last_mrf_write[reg], n);
         last_mrf_write[reg] = n;
         if (is_compressed(inst)) {
            if (inst->dst.reg & BRW_MRF_COMPR4)
               reg += 4;
            else
               reg++;
            add_dep(last_mrf_write[reg], n);
            last_mrf_write[reg] = n;
         }
      } else if (inst->dst.file == FIXED_HW_REG &&
                 inst->dst.fixed_hw_reg.file == BRW_GENERAL_REGISTER_FILE) {
         if (post_reg_alloc) {
            for (int r = 0; r < reg_width; r++)
               last_grf_write[inst->dst.fixed_hw_reg.nr + r] = n;
         } else {
            last_fixed_grf_write = n;
         }
      } else if (inst->dst.file != BAD_FILE) {
         add_barrier_deps(n);
      }

      if (inst->mlen > 0) {
         for (int i = 0; i < v->implied_mrf_writes(inst); i++) {
            add_dep(last_mrf_write[inst->base_mrf + i], n);
            last_mrf_write[inst->base_mrf + i] = n;
         }
      }

      /* Treat FS_OPCODE_MOV_DISPATCH_TO_FLAGS as though it had a
       * conditional_mod, because it sets the flag register.
       */
      if (inst->conditional_mod ||
          inst->opcode == FS_OPCODE_MOV_DISPATCH_TO_FLAGS) {
         add_dep(last_conditional_mod[inst->flag_subreg], n, 0);
         last_conditional_mod[inst->flag_subreg] = n;
      }
   }

   /* bottom-to-top dependencies: WAR */
   memset(last_grf_write, 0, sizeof(last_grf_write));
   memset(last_mrf_write, 0, sizeof(last_mrf_write));
   memset(last_conditional_mod, 0, sizeof(last_conditional_mod));
   last_fixed_grf_write = NULL;

   exec_node *node;
   exec_node *prev;
   for (node = instructions.get_tail(), prev = node->prev;
        !node->is_head_sentinel();
        node = prev, prev = node->prev) {
      schedule_node *n = (schedule_node *)node;
      fs_inst *inst = n->inst;

      /* write-after-read deps. */
      for (int i = 0; i < 3; i++) {
         if (inst->src[i].file == GRF) {
            if (post_reg_alloc) {
               for (int r = 0; r < reg_width; r++)
                  add_dep(n, last_grf_write[inst->src[i].reg + r]);
            } else {
               add_dep(n, last_grf_write[inst->src[i].reg]);
            }
         } else if (inst->src[i].file == FIXED_HW_REG &&
                    (inst->src[i].fixed_hw_reg.file ==
                     BRW_GENERAL_REGISTER_FILE)) {
            if (post_reg_alloc) {
               for (int r = 0; r < reg_width; r++)
                  add_dep(n, last_grf_write[inst->src[i].fixed_hw_reg.nr + r]);
            } else {
               add_dep(n, last_fixed_grf_write);
            }
         } else if (inst->src[i].file != BAD_FILE &&
                    inst->src[i].file != IMM &&
                    inst->src[i].file != UNIFORM) {
            assert(inst->src[i].file != MRF);
            add_barrier_deps(n);
         }
      }

      for (int i = 0; i < inst->mlen; i++) {
         /* It looks like the MRF regs are released in the send
          * instruction once it's sent, not when the result comes
          * back.
          */
         add_dep(n, last_mrf_write[inst->base_mrf + i], 2);
      }

      if (inst->predicate) {
         add_dep(n, last_conditional_mod[inst->flag_subreg]);
      }

      /* Update the things this instruction wrote, so earlier reads
       * can mark this as WAR dependency.
       */
      if (inst->dst.file == GRF) {
         if (post_reg_alloc) {
            for (int r = 0; r < inst->regs_written() * reg_width; r++)
               last_grf_write[inst->dst.reg + r] = n;
         } else {
            last_grf_write[inst->dst.reg] = n;
         }
      } else if (inst->dst.file == MRF) {
         int reg = inst->dst.reg & ~BRW_MRF_COMPR4;

         last_mrf_write[reg] = n;

         if (is_compressed(inst)) {
            if (inst->dst.reg & BRW_MRF_COMPR4)
               reg += 4;
            else
               reg++;

            last_mrf_write[reg] = n;
         }
      } else if (inst->dst.file == FIXED_HW_REG &&
                 inst->dst.fixed_hw_reg.file == BRW_GENERAL_REGISTER_FILE) {
         if (post_reg_alloc) {
            for (int r = 0; r < reg_width; r++)
               last_grf_write[inst->dst.fixed_hw_reg.nr + r] = n;
         } else {
            last_fixed_grf_write = n;
         }
      } else if (inst->dst.file != BAD_FILE) {
         add_barrier_deps(n);
      }

      if (inst->mlen > 0) {
         for (int i = 0; i < v->implied_mrf_writes(inst); i++) {
            last_mrf_write[inst->base_mrf + i] = n;
         }
      }

      /* Treat FS_OPCODE_MOV_DISPATCH_TO_FLAGS as though it had a
       * conditional_mod, because it sets the flag register.
       */
      if (inst->conditional_mod ||
          inst->opcode == FS_OPCODE_MOV_DISPATCH_TO_FLAGS) {
         last_conditional_mod[inst->flag_subreg] = n;
      }
   }
}

void
instruction_scheduler::schedule_instructions(fs_inst *next_block_header)
{
   int time = 0;

   /* Remove non-DAG heads from the list. */
   foreach_list_safe(node, &instructions) {
      schedule_node *n = (schedule_node *)node;
      if (n->parent_count != 0)
         n->remove();
   }

   while (!instructions.is_empty()) {
      schedule_node *chosen = NULL;
      int chosen_time = 0;

      if (post_reg_alloc) {
         /* Of the instructions closest ready to execute or the closest to
          * being ready, choose the oldest one.
          */
         foreach_list(node, &instructions) {
            schedule_node *n = (schedule_node *)node;

            if (!chosen || n->unblocked_time < chosen_time) {
               chosen = n;
               chosen_time = n->unblocked_time;
            }
         }
      } else {
         /* Before register allocation, we don't care about the latencies of
          * instructions.  All we care about is reducing live intervals of
          * variables so that we can avoid register spilling, or get 16-wide
          * shaders which naturally do a better job of hiding instruction
          * latency.
          *
          * To do so, schedule our instructions in a roughly LIFO/depth-first
          * order: when new instructions become available as a result of
          * scheduling something, choose those first so that our result
          * hopefully is consumed quickly.
          *
          * The exception is messages that generate more than one result
          * register (AKA texturing).  In those cases, the LIFO search would
          * normally tend to choose them quickly (because scheduling the
          * previous message not only unblocked the children using its result,
          * but also the MRF setup for the next sampler message, which in turn
          * unblocks the next sampler message).
          */
         for (schedule_node *node = (schedule_node *)instructions.get_tail();
              node != instructions.get_head()->prev;
              node = (schedule_node *)node->prev) {
            schedule_node *n = (schedule_node *)node;

            chosen = n;
            if (chosen->inst->regs_written() <= 1)
               break;
         }

         chosen_time = chosen->unblocked_time;
      }

      /* Schedule this instruction. */
      assert(chosen);
      chosen->remove();
      next_block_header->insert_before(chosen->inst);
      instructions_to_schedule--;

      /* Bump the clock.  Instructions in gen hardware are handled one simd4
       * vector at a time, with 1 cycle per vector dispatched.  Thus 8-wide
       * pixel shaders take 2 cycles to dispatch and 16-wide (compressed)
       * instructions take 4.
       */
      if (is_compressed(chosen->inst))
         time += 4;
      else
         time += 2;

      /* If we expected a delay for scheduling, then bump the clock to reflect
       * that as well.  In reality, the hardware will switch to another
       * hyperthread and may not return to dispatching our thread for a while
       * even after we're unblocked.
       */
      time = MAX2(time, chosen_time);

      if (debug) {
         printf("clock %4d, scheduled: ", time);
         v->dump_instruction(chosen->inst);
      }

      /* Now that we've scheduled a new instruction, some of its
       * children can be promoted to the list of instructions ready to
       * be scheduled.  Update the children's unblocked time for this
       * DAG edge as we do so.
       */
      for (int i = 0; i < chosen->child_count; i++) {
         schedule_node *child = chosen->children[i];

         child->unblocked_time = MAX2(child->unblocked_time,
                                      time + chosen->child_latency[i]);

         child->parent_count--;
         if (child->parent_count == 0) {
            if (debug) {
               printf("now available: ");
               v->dump_instruction(child->inst);
            }
            instructions.push_tail(child);
         }
      }

      /* Shared resource: the mathbox.  There's one mathbox per EU on Gen6+
       * but it's more limited pre-gen6, so if we send something off to it then
       * the next math instruction isn't going to make progress until the first
       * is done.
       */
      if (chosen->inst->is_math()) {
         foreach_list(node, &instructions) {
            schedule_node *n = (schedule_node *)node;

            if (n->inst->is_math())
               n->unblocked_time = MAX2(n->unblocked_time,
                                        time + chosen->latency);
         }
      }
   }

   assert(instructions_to_schedule == 0);
}

void
fs_visitor::schedule_instructions(bool post_reg_alloc)
{
   fs_inst *next_block_header = (fs_inst *)instructions.head;

   int grf_count;
   if (post_reg_alloc)
      grf_count = grf_used;
   else
      grf_count = virtual_grf_count;

   if (debug) {
      printf("\nInstructions before scheduling (reg_alloc %d)\n", post_reg_alloc);
      dump_instructions();
   }

   instruction_scheduler sched(this, mem_ctx, grf_count, post_reg_alloc);

   while (!next_block_header->is_tail_sentinel()) {
      /* Add things to be scheduled until we get to a new BB. */
      while (!next_block_header->is_tail_sentinel()) {
         fs_inst *inst = next_block_header;
         next_block_header = (fs_inst *)next_block_header->next;

         sched.add_inst(inst);
         if (inst->is_control_flow())
            break;
      }
      sched.calculate_deps();
      sched.schedule_instructions(next_block_header);
   }

   if (debug) {
      printf("\nInstructions after scheduling (reg_alloc %d)\n", post_reg_alloc);
      dump_instructions();
   }

   this->live_intervals_valid = false;
}