nir_loop_analyze.c 37.3 KB
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/*
 * Copyright © 2015 Thomas Helland
 *
 * 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 "nir.h"
#include "nir_constant_expressions.h"
#include "nir_loop_analyze.h"

typedef enum {
   undefined,
   invariant,
   not_invariant,
   basic_induction
} nir_loop_variable_type;

struct nir_basic_induction_var;

typedef struct {
   /* A link for the work list */
   struct list_head process_link;

   bool in_loop;

   /* The ssa_def associated with this info */
   nir_ssa_def *def;

   /* The type of this ssa_def */
   nir_loop_variable_type type;

   /* If this is of type basic_induction */
   struct nir_basic_induction_var *ind;

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   /* True if variable is in an if branch */
   bool in_if_branch;

   /* True if variable is in a nested loop */
   bool in_nested_loop;
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} nir_loop_variable;

typedef struct nir_basic_induction_var {
   nir_op alu_op;                           /* The type of alu-operation    */
   nir_loop_variable *alu_def;              /* The def of the alu-operation */
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   nir_alu_src *invariant;                  /* The invariant alu-src        */
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   nir_loop_variable *def_outside_loop;     /* The phi-src outside the loop */
} nir_basic_induction_var;

typedef struct {
   /* The loop we store information for */
   nir_loop *loop;

   /* Loop_variable for all ssa_defs in function */
   nir_loop_variable *loop_vars;

   /* A list of the loop_vars to analyze */
   struct list_head process_list;

   nir_variable_mode indirect_mask;

} loop_info_state;

static nir_loop_variable *
get_loop_var(nir_ssa_def *value, loop_info_state *state)
{
   return &(state->loop_vars[value->index]);
}

typedef struct {
   loop_info_state *state;
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   bool in_if_branch;
   bool in_nested_loop;
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} init_loop_state;

static bool
init_loop_def(nir_ssa_def *def, void *void_init_loop_state)
{
   init_loop_state *loop_init_state = void_init_loop_state;
   nir_loop_variable *var = get_loop_var(def, loop_init_state->state);

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   if (loop_init_state->in_nested_loop) {
      var->in_nested_loop = true;
   } else if (loop_init_state->in_if_branch) {
      var->in_if_branch = true;
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   } else {
      /* Add to the tail of the list. That way we start at the beginning of
       * the defs in the loop instead of the end when walking the list. This
       * means less recursive calls. Only add defs that are not in nested
       * loops or conditional blocks.
       */
      list_addtail(&var->process_link, &loop_init_state->state->process_list);
   }

   var->in_loop = true;

   return true;
}

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/** Calculate an estimated cost in number of instructions
 *
 * We do this so that we don't unroll loops which will later get massively
 * inflated due to int64 or fp64 lowering.  The estimates provided here don't
 * have to be massively accurate; they just have to be good enough that loop
 * unrolling doesn't cause things to blow up too much.
 */
static unsigned
instr_cost(nir_instr *instr, const nir_shader_compiler_options *options)
{
   if (instr->type == nir_instr_type_intrinsic ||
       instr->type == nir_instr_type_tex)
      return 1;

   if (instr->type != nir_instr_type_alu)
      return 0;

   nir_alu_instr *alu = nir_instr_as_alu(instr);
   const nir_op_info *info = &nir_op_infos[alu->op];

   /* Assume everything 16 or 32-bit is cheap.
    *
    * There are no 64-bit ops that don't have a 64-bit thing as their
    * destination or first source.
    */
   if (nir_dest_bit_size(alu->dest.dest) < 64 &&
       nir_src_bit_size(alu->src[0].src) < 64)
      return 1;

   bool is_fp64 = nir_dest_bit_size(alu->dest.dest) == 64 &&
      nir_alu_type_get_base_type(info->output_type) == nir_type_float;
   for (unsigned i = 0; i < info->num_inputs; i++) {
      if (nir_src_bit_size(alu->src[i].src) == 64 &&
          nir_alu_type_get_base_type(info->input_types[i]) == nir_type_float)
         is_fp64 = true;
   }

   if (is_fp64) {
      /* If it's something lowered normally, it's expensive. */
      unsigned cost = 1;
      if (options->lower_doubles_options &
          nir_lower_doubles_op_to_options_mask(alu->op))
         cost *= 20;

      /* If it's full software, it's even more expensive */
      if (options->lower_doubles_options & nir_lower_fp64_full_software)
         cost *= 100;

      return cost;
   } else {
      if (options->lower_int64_options &
          nir_lower_int64_op_to_options_mask(alu->op)) {
         /* These require a doing the division algorithm. */
         if (alu->op == nir_op_idiv || alu->op == nir_op_udiv ||
             alu->op == nir_op_imod || alu->op == nir_op_umod ||
             alu->op == nir_op_irem)
            return 100;

         /* Other int64 lowering isn't usually all that expensive */
         return 5;
      }

      return 1;
   }
}

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static bool
init_loop_block(nir_block *block, loop_info_state *state,
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                bool in_if_branch, bool in_nested_loop,
                const nir_shader_compiler_options *options)
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{
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   init_loop_state init_state = {.in_if_branch = in_if_branch,
                                 .in_nested_loop = in_nested_loop,
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                                 .state = state };

   nir_foreach_instr(instr, block) {
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      state->loop->info->instr_cost += instr_cost(instr, options);
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      nir_foreach_ssa_def(instr, init_loop_def, &init_state);
   }

   return true;
}

static inline bool
is_var_alu(nir_loop_variable *var)
{
   return var->def->parent_instr->type == nir_instr_type_alu;
}

static inline bool
is_var_constant(nir_loop_variable *var)
{
   return var->def->parent_instr->type == nir_instr_type_load_const;
}

static inline bool
is_var_phi(nir_loop_variable *var)
{
   return var->def->parent_instr->type == nir_instr_type_phi;
}

static inline bool
mark_invariant(nir_ssa_def *def, loop_info_state *state)
{
   nir_loop_variable *var = get_loop_var(def, state);

   if (var->type == invariant)
      return true;

   if (!var->in_loop) {
      var->type = invariant;
      return true;
   }

   if (var->type == not_invariant)
      return false;

   if (is_var_alu(var)) {
      nir_alu_instr *alu = nir_instr_as_alu(def->parent_instr);

      for (unsigned i = 0; i < nir_op_infos[alu->op].num_inputs; i++) {
         if (!mark_invariant(alu->src[i].src.ssa, state)) {
            var->type = not_invariant;
            return false;
         }
      }
      var->type = invariant;
      return true;
   }

   /* Phis shouldn't be invariant except if one operand is invariant, and the
    * other is the phi itself. These should be removed by opt_remove_phis.
    * load_consts are already set to invariant and constant during init,
    * and so should return earlier. Remaining op_codes are set undefined.
    */
   var->type = not_invariant;
   return false;
}

static void
compute_invariance_information(loop_info_state *state)
{
   /* An expression is invariant in a loop L if:
    *  (base cases)
    *    – it’s a constant
    *    – it’s a variable use, all of whose single defs are outside of L
    *  (inductive cases)
    *    – it’s a pure computation all of whose args are loop invariant
    *    – it’s a variable use whose single reaching def, and the
    *      rhs of that def is loop-invariant
    */
   list_for_each_entry_safe(nir_loop_variable, var, &state->process_list,
                            process_link) {
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      assert(!var->in_if_branch && !var->in_nested_loop);
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      if (mark_invariant(var->def, state))
         list_del(&var->process_link);
   }
}

static bool
compute_induction_information(loop_info_state *state)
{
   bool found_induction_var = false;
   list_for_each_entry_safe(nir_loop_variable, var, &state->process_list,
                            process_link) {

      /* It can't be an induction variable if it is invariant. Invariants and
       * things in nested loops or conditionals should have been removed from
       * the list by compute_invariance_information().
       */
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      assert(!var->in_if_branch && !var->in_nested_loop &&
             var->type != invariant);
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      /* We are only interested in checking phis for the basic induction
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       * variable case as its simple to detect. All basic induction variables
       * have a phi node
       */
      if (!is_var_phi(var))
         continue;

      nir_phi_instr *phi = nir_instr_as_phi(var->def->parent_instr);
      nir_basic_induction_var *biv = rzalloc(state, nir_basic_induction_var);

      nir_foreach_phi_src(src, phi) {
         nir_loop_variable *src_var = get_loop_var(src->src.ssa, state);

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         /* If one of the sources is in an if branch or nested loop then don't
          * attempt to go any further.
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          */
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         if (src_var->in_if_branch || src_var->in_nested_loop)
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            break;

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         /* Detect inductions variables that are incremented in both branches
          * of an unnested if rather than in a loop block.
          */
         if (is_var_phi(src_var)) {
            nir_phi_instr *src_phi =
               nir_instr_as_phi(src_var->def->parent_instr);

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            nir_op alu_op = nir_num_opcodes; /* avoid uninitialized warning */
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            nir_ssa_def *alu_srcs[2] = {0};
            nir_foreach_phi_src(src2, src_phi) {
               nir_loop_variable *src_var2 =
                  get_loop_var(src2->src.ssa, state);

               if (!src_var2->in_if_branch || !is_var_alu(src_var2))
                  break;

               nir_alu_instr *alu =
                  nir_instr_as_alu(src_var2->def->parent_instr);
               if (nir_op_infos[alu->op].num_inputs != 2)
                  break;

               if (alu->src[0].src.ssa == alu_srcs[0] &&
                   alu->src[1].src.ssa == alu_srcs[1] &&
                   alu->op == alu_op) {
                  /* Both branches perform the same calculation so we can use
                   * one of them to find the induction variable.
                   */
                  src_var = src_var2;
               } else {
                  alu_srcs[0] = alu->src[0].src.ssa;
                  alu_srcs[1] = alu->src[1].src.ssa;
                  alu_op = alu->op;
               }
            }
         }

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         if (!src_var->in_loop) {
            biv->def_outside_loop = src_var;
         } else if (is_var_alu(src_var)) {
            nir_alu_instr *alu = nir_instr_as_alu(src_var->def->parent_instr);

            if (nir_op_infos[alu->op].num_inputs == 2) {
               biv->alu_def = src_var;
               biv->alu_op = alu->op;

               for (unsigned i = 0; i < 2; i++) {
                  /* Is one of the operands const, and the other the phi */
                  if (alu->src[i].src.ssa->parent_instr->type == nir_instr_type_load_const &&
                      alu->src[1-i].src.ssa == &phi->dest.ssa)
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                     biv->invariant = &alu->src[i];
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               }
            }
         }
      }

      if (biv->alu_def && biv->def_outside_loop && biv->invariant &&
          is_var_constant(biv->def_outside_loop)) {
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         assert(is_var_constant(get_loop_var(biv->invariant->src.ssa, state)));
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         biv->alu_def->type = basic_induction;
         biv->alu_def->ind = biv;
         var->type = basic_induction;
         var->ind = biv;

         found_induction_var = true;
      } else {
         ralloc_free(biv);
      }
   }
   return found_induction_var;
}

static bool
initialize_ssa_def(nir_ssa_def *def, void *void_state)
{
   loop_info_state *state = void_state;
   nir_loop_variable *var = get_loop_var(def, state);

   var->in_loop = false;
   var->def = def;

   if (def->parent_instr->type == nir_instr_type_load_const) {
      var->type = invariant;
   } else {
      var->type = undefined;
   }

   return true;
}

static bool
find_loop_terminators(loop_info_state *state)
{
   bool success = false;
   foreach_list_typed_safe(nir_cf_node, node, node, &state->loop->body) {
      if (node->type == nir_cf_node_if) {
         nir_if *nif = nir_cf_node_as_if(node);

         nir_block *break_blk = NULL;
         nir_block *continue_from_blk = NULL;
         bool continue_from_then = true;

         nir_block *last_then = nir_if_last_then_block(nif);
         nir_block *last_else = nir_if_last_else_block(nif);
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         if (nir_block_ends_in_break(last_then)) {
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            break_blk = last_then;
            continue_from_blk = last_else;
            continue_from_then = false;
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         } else if (nir_block_ends_in_break(last_else)) {
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            break_blk = last_else;
            continue_from_blk = last_then;
         }

         /* If there is a break then we should find a terminator. If we can
          * not find a loop terminator, but there is a break-statement then
          * we should return false so that we do not try to find trip-count
          */
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         if (!nir_is_trivial_loop_if(nif, break_blk)) {
            state->loop->info->complex_loop = true;
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            return false;
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         }
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         /* Continue if the if contained no jumps at all */
         if (!break_blk)
            continue;

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         if (nif->condition.ssa->parent_instr->type == nir_instr_type_phi) {
            state->loop->info->complex_loop = true;
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            return false;
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         }
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         nir_loop_terminator *terminator =
            rzalloc(state->loop->info, nir_loop_terminator);

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         list_addtail(&terminator->loop_terminator_link,
                      &state->loop->info->loop_terminator_list);
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         terminator->nif = nif;
         terminator->break_block = break_blk;
         terminator->continue_from_block = continue_from_blk;
         terminator->continue_from_then = continue_from_then;
         terminator->conditional_instr = nif->condition.ssa->parent_instr;

         success = true;
      }
   }

   return success;
}

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/* This function looks for an array access within a loop that uses an
 * induction variable for the array index. If found it returns the size of the
 * array, otherwise 0 is returned. If we find an induction var we pass it back
 * to the caller via array_index_out.
 */
static unsigned
find_array_access_via_induction(loop_info_state *state,
                                nir_deref_instr *deref,
                                nir_loop_variable **array_index_out)
{
   for (nir_deref_instr *d = deref; d; d = nir_deref_instr_parent(d)) {
      if (d->deref_type != nir_deref_type_array)
         continue;

      assert(d->arr.index.is_ssa);
      nir_loop_variable *array_index = get_loop_var(d->arr.index.ssa, state);

      if (array_index->type != basic_induction)
         continue;

      if (array_index_out)
         *array_index_out = array_index;

      nir_deref_instr *parent = nir_deref_instr_parent(d);
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      if (glsl_type_is_array_or_matrix(parent->type)) {
         return glsl_get_length(parent->type);
      } else {
         assert(glsl_type_is_vector(parent->type));
         return glsl_get_vector_elements(parent->type);
      }
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   }

   return 0;
}

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static bool
guess_loop_limit(loop_info_state *state, nir_const_value *limit_val,
                 nir_loop_variable *basic_ind)
{
   unsigned min_array_size = 0;

   nir_foreach_block_in_cf_node(block, &state->loop->cf_node) {
      nir_foreach_instr(instr, block) {
         if (instr->type != nir_instr_type_intrinsic)
            continue;

         nir_intrinsic_instr *intrin = nir_instr_as_intrinsic(instr);

         /* Check for arrays variably-indexed by a loop induction variable. */
         if (intrin->intrinsic == nir_intrinsic_load_deref ||
             intrin->intrinsic == nir_intrinsic_store_deref ||
             intrin->intrinsic == nir_intrinsic_copy_deref) {

            nir_loop_variable *array_idx = NULL;
            unsigned array_size =
               find_array_access_via_induction(state,
                                               nir_src_as_deref(intrin->src[0]),
                                               &array_idx);
            if (basic_ind == array_idx &&
                (min_array_size == 0 || min_array_size > array_size)) {
               min_array_size = array_size;
            }

            if (intrin->intrinsic != nir_intrinsic_copy_deref)
               continue;

            array_size =
               find_array_access_via_induction(state,
                                               nir_src_as_deref(intrin->src[1]),
                                               &array_idx);
            if (basic_ind == array_idx &&
                (min_array_size == 0 || min_array_size > array_size)) {
               min_array_size = array_size;
            }
         }
      }
   }

   if (min_array_size) {
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      limit_val->i32 = min_array_size;
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      return true;
   }

   return false;
}

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static bool
try_find_limit_of_alu(nir_loop_variable *limit, nir_const_value *limit_val,
                      nir_loop_terminator *terminator, loop_info_state *state)
{
   if(!is_var_alu(limit))
      return false;

   nir_alu_instr *limit_alu = nir_instr_as_alu(limit->def->parent_instr);

   if (limit_alu->op == nir_op_imin ||
       limit_alu->op == nir_op_fmin) {
      limit = get_loop_var(limit_alu->src[0].src.ssa, state);

      if (!is_var_constant(limit))
         limit = get_loop_var(limit_alu->src[1].src.ssa, state);

      if (!is_var_constant(limit))
         return false;

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      *limit_val = nir_instr_as_load_const(limit->def->parent_instr)->value[0];
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      terminator->exact_trip_count_unknown = true;

      return true;
   }

   return false;
}

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static int32_t
get_iteration(nir_op cond_op, nir_const_value *initial, nir_const_value *step,
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              nir_const_value *limit)
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{
   int32_t iter;

   switch (cond_op) {
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   case nir_op_ige:
   case nir_op_ilt:
   case nir_op_ieq:
   case nir_op_ine: {
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      int32_t initial_val = initial->i32;
      int32_t span = limit->i32 - initial_val;
      iter = span / step->i32;
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      break;
   }
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   case nir_op_uge:
   case nir_op_ult: {
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      uint32_t initial_val = initial->u32;
      uint32_t span = limit->u32 - initial_val;
      iter = span / step->u32;
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      break;
   }
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   case nir_op_fge:
   case nir_op_flt:
   case nir_op_feq:
   case nir_op_fne: {
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      float initial_val = initial->f32;
      float span = limit->f32 - initial_val;
      iter = span / step->f32;
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      break;
   }
   default:
      return -1;
   }

   return iter;
}

static bool
test_iterations(int32_t iter_int, nir_const_value *step,
                nir_const_value *limit, nir_op cond_op, unsigned bit_size,
                nir_alu_type induction_base_type,
                nir_const_value *initial, bool limit_rhs, bool invert_cond)
{
   assert(nir_op_infos[cond_op].num_inputs == 2);

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   nir_const_value iter_src = {0, };
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   nir_op mul_op;
   nir_op add_op;
   switch (induction_base_type) {
   case nir_type_float:
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      iter_src.f32 = (float) iter_int;
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      mul_op = nir_op_fmul;
      add_op = nir_op_fadd;
      break;
   case nir_type_int:
   case nir_type_uint:
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      iter_src.i32 = iter_int;
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      mul_op = nir_op_imul;
      add_op = nir_op_iadd;
      break;
   default:
      unreachable("Unhandled induction variable base type!");
   }

   /* Multiple the iteration count we are testing by the number of times we
    * step the induction variable each iteration.
    */
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   nir_const_value *mul_src[2] = { &iter_src, step };
   nir_const_value mul_result;
   nir_eval_const_opcode(mul_op, &mul_result, 1, bit_size, mul_src);
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   /* Add the initial value to the accumulated induction variable total */
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   nir_const_value *add_src[2] = { &mul_result, initial };
   nir_const_value add_result;
   nir_eval_const_opcode(add_op, &add_result, 1, bit_size, add_src);
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   nir_const_value *src[2];
   src[limit_rhs ? 0 : 1] = &add_result;
   src[limit_rhs ? 1 : 0] = limit;
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   /* Evaluate the loop exit condition */
657 658
   nir_const_value result;
   nir_eval_const_opcode(cond_op, &result, 1, bit_size, src);
659

660
   return invert_cond ? !result.b : result.b;
661 662 663 664 665
}

static int
calculate_iterations(nir_const_value *initial, nir_const_value *step,
                     nir_const_value *limit, nir_loop_variable *alu_def,
666 667
                     nir_alu_instr *cond_alu, nir_op alu_op, bool limit_rhs,
                     bool invert_cond)
668 669 670 671 672 673 674 675 676 677 678 679 680 681
{
   assert(initial != NULL && step != NULL && limit != NULL);

   nir_alu_instr *alu = nir_instr_as_alu(alu_def->def->parent_instr);

   /* nir_op_isub should have been lowered away by this point */
   assert(alu->op != nir_op_isub);

   /* Make sure the alu type for our induction variable is compatible with the
    * conditional alus input type. If its not something has gone really wrong.
    */
   nir_alu_type induction_base_type =
      nir_alu_type_get_base_type(nir_op_infos[alu->op].output_type);
   if (induction_base_type == nir_type_int || induction_base_type == nir_type_uint) {
682 683
      assert(nir_alu_type_get_base_type(nir_op_infos[alu_op].input_types[1]) == nir_type_int ||
             nir_alu_type_get_base_type(nir_op_infos[alu_op].input_types[1]) == nir_type_uint);
684
   } else {
685
      assert(nir_alu_type_get_base_type(nir_op_infos[alu_op].input_types[0]) ==
686 687 688 689 690 691 692 693 694 695 696 697 698 699 700 701 702 703 704 705 706 707 708
             induction_base_type);
   }

   /* Check for nsupported alu operations */
   if (alu->op != nir_op_iadd && alu->op != nir_op_fadd)
      return -1;

   /* do-while loops can increment the starting value before the condition is
    * checked. e.g.
    *
    *    do {
    *        ndx++;
    *     } while (ndx < 3);
    *
    * Here we check if the induction variable is used directly by the loop
    * condition and if so we assume we need to step the initial value.
    */
   unsigned trip_offset = 0;
   if (cond_alu->src[0].src.ssa == alu_def->def ||
       cond_alu->src[1].src.ssa == alu_def->def) {
      trip_offset = 1;
   }

709
   int iter_int = get_iteration(alu_op, initial, step, limit);
710 711 712 713 714 715 716 717 718 719 720 721 722 723 724 725 726 727 728 729 730 731

   /* If iter_int is negative the loop is ill-formed or is the conditional is
    * unsigned with a huge iteration count so don't bother going any further.
    */
   if (iter_int < 0)
      return -1;

   /* An explanation from the GLSL unrolling pass:
    *
    * Make sure that the calculated number of iterations satisfies the exit
    * condition.  This is needed to catch off-by-one errors and some types of
    * ill-formed loops.  For example, we need to detect that the following
    * loop does not have a maximum iteration count.
    *
    *    for (float x = 0.0; x != 0.9; x += 0.2);
    */
   assert(nir_src_bit_size(alu->src[0].src) ==
          nir_src_bit_size(alu->src[1].src));
   unsigned bit_size = nir_src_bit_size(alu->src[0].src);
   for (int bias = -1; bias <= 1; bias++) {
      const int iter_bias = iter_int + bias;

732
      if (test_iterations(iter_bias, step, limit, alu_op, bit_size,
733 734 735 736 737 738 739 740 741
                          induction_base_type, initial,
                          limit_rhs, invert_cond)) {
         return iter_bias > 0 ? iter_bias - trip_offset : iter_bias;
      }
   }

   return -1;
}

742 743 744 745 746 747 748 749 750 751 752 753 754 755 756 757 758 759 760 761 762 763 764 765 766 767 768 769 770
static nir_op
inverse_comparison(nir_alu_instr *alu)
{
   switch (alu->op) {
   case nir_op_fge:
      return nir_op_flt;
   case nir_op_ige:
      return nir_op_ilt;
   case nir_op_uge:
      return nir_op_ult;
   case nir_op_flt:
      return nir_op_fge;
   case nir_op_ilt:
      return nir_op_ige;
   case nir_op_ult:
      return nir_op_uge;
   case nir_op_feq:
      return nir_op_fne;
   case nir_op_ieq:
      return nir_op_ine;
   case nir_op_fne:
      return nir_op_feq;
   case nir_op_ine:
      return nir_op_ieq;
   default:
      unreachable("Unsuported comparison!");
   }
}

771 772 773 774 775 776 777
static bool
is_supported_terminator_condition(nir_alu_instr *alu)
{
   return nir_alu_instr_is_comparison(alu) &&
          nir_op_infos[alu->op].num_inputs == 2;
}

778 779 780 781 782 783 784 785 786 787 788 789 790 791 792 793 794 795 796 797 798
static bool
get_induction_and_limit_vars(nir_alu_instr *alu, nir_loop_variable **ind,
                             nir_loop_variable **limit,
                             loop_info_state *state)
{
   bool limit_rhs = true;

   /* We assume that the limit is the "right" operand */
   *ind = get_loop_var(alu->src[0].src.ssa, state);
   *limit = get_loop_var(alu->src[1].src.ssa, state);

   if ((*ind)->type != basic_induction) {
      /* We had it the wrong way, flip things around */
      *ind = get_loop_var(alu->src[1].src.ssa, state);
      *limit = get_loop_var(alu->src[0].src.ssa, state);
      limit_rhs = false;
   }

   return limit_rhs;
}

799 800 801 802 803 804 805 806 807 808 809 810 811 812 813 814 815 816 817 818 819 820 821 822 823 824 825
static void
try_find_trip_count_vars_in_iand(nir_alu_instr **alu,
                                 nir_loop_variable **ind,
                                 nir_loop_variable **limit,
                                 bool *limit_rhs,
                                 loop_info_state *state)
{
   assert((*alu)->op == nir_op_ieq || (*alu)->op == nir_op_inot);

   nir_ssa_def *iand_def = (*alu)->src[0].src.ssa;

   if ((*alu)->op == nir_op_ieq) {
      nir_ssa_def *zero_def = (*alu)->src[1].src.ssa;

      if (iand_def->parent_instr->type != nir_instr_type_alu ||
          zero_def->parent_instr->type != nir_instr_type_load_const) {

         /* Maybe we had it the wrong way, flip things around */
         iand_def = (*alu)->src[1].src.ssa;
         zero_def = (*alu)->src[0].src.ssa;

         /* If we still didn't find what we need then return */
         if (zero_def->parent_instr->type != nir_instr_type_load_const)
            return;
      }

      /* If the loop is not breaking on (x && y) == 0 then return */
826
      nir_const_value *zero =
827
         nir_instr_as_load_const(zero_def->parent_instr)->value;
828
      if (zero[0].i32 != 0)
829 830 831 832 833 834 835 836 837 838 839 840 841 842 843 844 845 846 847 848 849
         return;
   }

   if (iand_def->parent_instr->type != nir_instr_type_alu)
      return;

   nir_alu_instr *iand = nir_instr_as_alu(iand_def->parent_instr);
   if (iand->op != nir_op_iand)
      return;

   /* Check if iand src is a terminator condition and try get induction var
    * and trip limit var.
    */
   nir_ssa_def *src = iand->src[0].src.ssa;
   if (src->parent_instr->type == nir_instr_type_alu) {
      *alu = nir_instr_as_alu(src->parent_instr);
      if (is_supported_terminator_condition(*alu))
         *limit_rhs = get_induction_and_limit_vars(*alu, ind, limit, state);
   }

   /* Try the other iand src if needed */
850
   if (*ind == NULL || (*ind && (*ind)->type != basic_induction) ||
851 852 853
       !is_var_constant(*limit)) {
      src = iand->src[1].src.ssa;
      if (src->parent_instr->type == nir_instr_type_alu) {
854 855 856
         nir_alu_instr *tmp_alu = nir_instr_as_alu(src->parent_instr);
         if (is_supported_terminator_condition(tmp_alu)) {
            *alu = tmp_alu;
857
            *limit_rhs = get_induction_and_limit_vars(*alu, ind, limit, state);
858
         }
859 860 861 862
      }
   }
}

863 864 865 866 867 868 869 870 871 872
/* Run through each of the terminators of the loop and try to infer a possible
 * trip-count. We need to check them all, and set the lowest trip-count as the
 * trip-count of our loop. If one of the terminators has an undecidable
 * trip-count we can not safely assume anything about the duration of the
 * loop.
 */
static void
find_trip_count(loop_info_state *state)
{
   bool trip_count_known = true;
873
   bool guessed_trip_count = false;
874
   nir_loop_terminator *limiting_terminator = NULL;
875
   int max_trip_count = -1;
876 877 878 879 880 881 882 883 884 885 886 887 888 889

   list_for_each_entry(nir_loop_terminator, terminator,
                       &state->loop->info->loop_terminator_list,
                       loop_terminator_link) {

      if (terminator->conditional_instr->type != nir_instr_type_alu) {
         /* If we get here the loop is dead and will get cleaned up by the
          * nir_opt_dead_cf pass.
          */
         trip_count_known = false;
         continue;
      }

      nir_alu_instr *alu = nir_instr_as_alu(terminator->conditional_instr);
890 891
      nir_op alu_op = alu->op;

892 893 894 895 896 897 898 899 900 901 902 903 904 905 906 907 908 909
      bool limit_rhs;
      nir_loop_variable *basic_ind = NULL;
      nir_loop_variable *limit;
      if (alu->op == nir_op_inot || alu->op == nir_op_ieq) {
         nir_alu_instr *new_alu = alu;
         try_find_trip_count_vars_in_iand(&new_alu, &basic_ind, &limit,
                                          &limit_rhs, state);

         /* The loop is exiting on (x && y) == 0 so we need to get the
          * inverse of x or y (i.e. which ever contained the induction var) in
          * order to compute the trip count.
          */
         if (basic_ind && basic_ind->type == basic_induction) {
            alu = new_alu;
            alu_op = inverse_comparison(alu);
            trip_count_known = false;
            terminator->exact_trip_count_unknown = true;
         }
910
      }
911

912 913 914 915 916 917 918 919 920
      if (!basic_ind) {
         if (!is_supported_terminator_condition(alu)) {
            trip_count_known = false;
            continue;
         }

         limit_rhs = get_induction_and_limit_vars(alu, &basic_ind, &limit,
                                                  state);
      }
921 922 923 924 925 926 927 928 929

      /* The comparison has to have a basic induction variable for us to be
       * able to find trip counts.
       */
      if (basic_ind->type != basic_induction) {
         trip_count_known = false;
         continue;
      }

930 931
      terminator->induction_rhs = !limit_rhs;

932 933 934 935
      /* Attempt to find a constant limit for the loop */
      nir_const_value limit_val;
      if (is_var_constant(limit)) {
         limit_val =
936
            nir_instr_as_load_const(limit->def->parent_instr)->value[0];
937 938
      } else {
         trip_count_known = false;
939

940 941 942 943
         if (!try_find_limit_of_alu(limit, &limit_val, terminator, state)) {
            /* Guess loop limit based on array access */
            if (!guess_loop_limit(state, &limit_val, basic_ind)) {
               continue;
944
            }
945

946 947 948
            guessed_trip_count = true;
         }
      }
949

950 951 952 953 954 955 956
      /* We have determined that we have the following constants:
       * (With the typical int i = 0; i < x; i++; as an example)
       *    - Upper limit.
       *    - Starting value
       *    - Step / iteration size
       * Thats all thats needed to calculate the trip-count
       */
957

958
      nir_const_value *initial_val =
959 960
         nir_instr_as_load_const(basic_ind->ind->def_outside_loop->
                                    def->parent_instr)->value;
961

962
      nir_const_value *step_val =
963 964
         nir_instr_as_load_const(basic_ind->ind->invariant->src.ssa->
                                 parent_instr)->value;
965

966
      int iterations = calculate_iterations(initial_val, step_val,
967 968
                                            &limit_val,
                                            basic_ind->ind->alu_def, alu,
969
                                            alu_op, limit_rhs,
970
                                            terminator->continue_from_then);
971

972 973 974 975 976 977
      /* Where we not able to calculate the iteration count */
      if (iterations == -1) {
         trip_count_known = false;
         guessed_trip_count = false;
         continue;
      }
978

979 980 981 982 983
      if (guessed_trip_count) {
         guessed_trip_count = false;
         if (state->loop->info->guessed_trip_count == 0 ||
             state->loop->info->guessed_trip_count > iterations)
            state->loop->info->guessed_trip_count = iterations;
984

985 986
         continue;
      }
987

988 989 990 991 992 993 994
      /* If this is the first run or we have found a smaller amount of
       * iterations than previously (we have identified a more limiting
       * terminator) set the trip count and limiting terminator.
       */
      if (max_trip_count == -1 || iterations < max_trip_count) {
         max_trip_count = iterations;
         limiting_terminator = terminator;
995 996 997
      }
   }

998 999 1000
   state->loop->info->exact_trip_count_known = trip_count_known;
   if (max_trip_count > -1)
      state->loop->info->max_trip_count = max_trip_count;
1001 1002 1003
   state->loop->info->limiting_terminator = limiting_terminator;
}

1004
static bool
1005
force_unroll_array_access(loop_info_state *state, nir_deref_instr *deref)
1006
{
1007 1008 1009
   unsigned array_size = find_array_access_via_induction(state, deref, NULL);
   if (array_size) {
      if (array_size == state->loop->info->max_trip_count)
1010 1011
         return true;

1012
      if (deref->mode & state->indirect_mask)
1013 1014 1015 1016 1017 1018
         return true;
   }

   return false;
}

1019
static bool
1020
force_unroll_heuristics(loop_info_state *state, nir_block *block)
1021 1022 1023 1024 1025 1026 1027 1028 1029 1030
{
   nir_foreach_instr(instr, block) {
      if (instr->type != nir_instr_type_intrinsic)
         continue;

      nir_intrinsic_instr *intrin = nir_instr_as_intrinsic(instr);

      /* Check for arrays variably-indexed by a loop induction variable.
       * Unrolling the loop may convert that access into constant-indexing.
       */
1031 1032 1033
      if (intrin->intrinsic == nir_intrinsic_load_deref ||
          intrin->intrinsic == nir_intrinsic_store_deref ||
          intrin->intrinsic == nir_intrinsic_copy_deref) {
1034
         if (force_unroll_array_access(state,
1035 1036 1037 1038
                                       nir_src_as_deref(intrin->src[0])))
            return true;

         if (intrin->intrinsic == nir_intrinsic_copy_deref &&
1039
             force_unroll_array_access(state,
1040 1041 1042
                                       nir_src_as_deref(intrin->src[1])))
            return true;
      }
1043 1044 1045 1046 1047 1048 1049 1050
   }

   return false;
}

static void
get_loop_info(loop_info_state *state, nir_function_impl *impl)
{
1051 1052 1053
   nir_shader *shader = impl->function->shader;
   const nir_shader_compiler_options *options = shader->options;

1054
   /* Initialize all variables to "outside_loop". This also marks defs
1055
    * invariant and constant if they are nir_instr_type_load_consts
1056 1057 1058 1059 1060 1061 1062 1063 1064 1065 1066 1067 1068
    */
   nir_foreach_block(block, impl) {
      nir_foreach_instr(instr, block)
         nir_foreach_ssa_def(instr, initialize_ssa_def, state);
   }

   /* Add all entries in the outermost part of the loop to the processing list
    * Mark the entries in conditionals or in nested loops accordingly
    */
   foreach_list_typed_safe(nir_cf_node, node, node, &state->loop->body) {
      switch (node->type) {

      case nir_cf_node_block:
1069 1070
         init_loop_block(nir_cf_node_as_block(node), state,
                         false, false, options);
1071 1072 1073 1074
         break;

      case nir_cf_node_if:
         nir_foreach_block_in_cf_node(block, node)
1075
            init_loop_block(block, state, true, false, options);
1076 1077 1078 1079
         break;

      case nir_cf_node_loop:
         nir_foreach_block_in_cf_node(block, node) {
1080
            init_loop_block(block, state, false, true, options);
1081 1082 1083 1084 1085 1086 1087 1088 1089 1090 1091 1092 1093 1094 1095 1096 1097 1098 1099 1100 1101
         }
         break;

      case nir_cf_node_function:
         break;
      }
   }

   /* Try to find all simple terminators of the loop. If we can't find any,
    * or we find possible terminators that have side effects then bail.
    */
   if (!find_loop_terminators(state)) {
      list_for_each_entry_safe(nir_loop_terminator, terminator,
                               &state->loop->info->loop_terminator_list,
                               loop_terminator_link) {
         list_del(&terminator->loop_terminator_link);
         ralloc_free(terminator);
      }
      return;
   }

1102 1103 1104 1105 1106 1107 1108
   /* Induction analysis needs invariance information so get that first */
   compute_invariance_information(state);

   /* We have invariance information so try to find induction variables */
   if (!compute_induction_information(state))
      return;

1109 1110 1111
   /* Run through each of the terminators and try to compute a trip-count */
   find_trip_count(state);

1112 1113 1114 1115
   nir_foreach_block_in_cf_node(block, &state->loop->cf_node) {
      if (force_unroll_heuristics(state, block)) {
         state->loop->info->force_unroll = true;
         break;
1116 1117 1118 1119 1120 1121 1122 1123 1124 1125 1126 1127 1128 1129 1130 1131 1132 1133 1134 1135 1136 1137 1138 1139 1140 1141 1142 1143 1144 1145 1146 1147 1148 1149 1150 1151 1152 1153 1154 1155 1156 1157 1158 1159 1160 1161 1162 1163 1164 1165 1166 1167 1168 1169 1170 1171 1172 1173 1174 1175 1176 1177 1178 1179 1180 1181 1182 1183 1184
      }
   }
}

static loop_info_state *
initialize_loop_info_state(nir_loop *loop, void *mem_ctx,
                           nir_function_impl *impl)
{
   loop_info_state *state = rzalloc(mem_ctx, loop_info_state);
   state->loop_vars = rzalloc_array(mem_ctx, nir_loop_variable,
                                    impl->ssa_alloc);
   state->loop = loop;

   list_inithead(&state->process_list);

   if (loop->info)
     ralloc_free(loop->info);

   loop->info = rzalloc(loop, nir_loop_info);

   list_inithead(&loop->info->loop_terminator_list);

   return state;
}

static void
process_loops(nir_cf_node *cf_node, nir_variable_mode indirect_mask)
{
   switch (cf_node->type) {
   case nir_cf_node_block:
      return;
   case nir_cf_node_if: {
      nir_if *if_stmt = nir_cf_node_as_if(cf_node);
      foreach_list_typed(nir_cf_node, nested_node, node, &if_stmt->then_list)
         process_loops(nested_node, indirect_mask);
      foreach_list_typed(nir_cf_node, nested_node, node, &if_stmt->else_list)
         process_loops(nested_node, indirect_mask);
      return;
   }
   case nir_cf_node_loop: {
      nir_loop *loop = nir_cf_node_as_loop(cf_node);
      foreach_list_typed(nir_cf_node, nested_node, node, &loop->body)
         process_loops(nested_node, indirect_mask);
      break;
   }
   default:
      unreachable("unknown cf node type");
   }

   nir_loop *loop = nir_cf_node_as_loop(cf_node);
   nir_function_impl *impl = nir_cf_node_get_function(cf_node);
   void *mem_ctx = ralloc_context(NULL);

   loop_info_state *state = initialize_loop_info_state(loop, mem_ctx, impl);
   state->indirect_mask = indirect_mask;

   get_loop_info(state, impl);

   ralloc_free(mem_ctx);
}

void
nir_loop_analyze_impl(nir_function_impl *impl,
                      nir_variable_mode indirect_mask)
{
   nir_index_ssa_defs(impl);
   foreach_list_typed(nir_cf_node, node, node, &impl->body)
      process_loops(node, indirect_mask);
}