src/compiler/nir/nir_opt_sink.c

   1 /*
   2  * Copyright © 2018 Red Hat
   3  * Copyright © 2019 Valve Corporation
   4  *
   5  * Permission is hereby granted, free of charge, to any person obtaining a
   6  * copy of this software and associated documentation files (the "Software"),
   7  * to deal in the Software without restriction, including without limitation
   8  * the rights to use, copy, modify, merge, publish, distribute, sublicense,
   9  * and/or sell copies of the Software, and to permit persons to whom the
  10  * Software is furnished to do so, subject to the following conditions:
  11  *
  12  * The above copyright notice and this permission notice (including the next
  13  * paragraph) shall be included in all copies or substantial portions of the
  14  * Software.
  15  *
  16  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  17  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  18  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
  19  * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  20  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
  21  * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
  22  * IN THE SOFTWARE.
  23  *
  24  * Authors:
  25  *    Rob Clark (robdclark@gmail.com>
  26  *    Daniel Schürmann (daniel.schuermann@campus.tu-berlin.de)
  27  *    Rhys Perry (pendingchaos02@gmail.com)
  28  *
  29  */
  30
  31 #include "nir.h"
  32
  33
  34 /*
  35  * A simple pass that moves some instructions into the least common
  36  * anscestor of consuming instructions.
  37  */
  38
  39 bool
  40 nir_can_move_instr(nir_instr *instr, nir_move_options options)
  41 {
  42    if ((options & nir_move_const_undef) && instr->type == nir_instr_type_load_const) {
  43       return true;
  44    }
  45
  46    if (instr->type == nir_instr_type_intrinsic) {
  47        nir_intrinsic_instr *intrin = nir_instr_as_intrinsic(instr);
  48       if ((options & nir_move_load_ubo) && intrin->intrinsic == nir_intrinsic_load_ubo)
  49          return true;
  50
  51       if ((options & nir_move_load_input) &&
  52           (intrin->intrinsic == nir_intrinsic_load_interpolated_input ||
  53            intrin->intrinsic == nir_intrinsic_load_input))
  54          return true;
  55    }
  56
  57    if ((options & nir_move_const_undef) && instr->type == nir_instr_type_ssa_undef) {
  58       return true;
  59    }
  60
  61    if ((options & nir_move_comparisons) && instr->type == nir_instr_type_alu &&
  62        nir_alu_instr_is_comparison(nir_instr_as_alu(instr))) {
  63       return true;
  64    }
  65
  66    return false;
  67 }
  68
  69 static nir_loop *
  70 get_innermost_loop(nir_cf_node *node)
  71 {
  72    for (; node != NULL; node = node->parent) {
  73       if (node->type == nir_cf_node_loop)
  74          return (nir_loop*)node;
  75    }
  76    return NULL;
  77 }
  78
  79 static bool
  80 loop_contains_block(nir_loop *loop, nir_block *block)
  81 {
  82    nir_block *before = nir_cf_node_as_block(nir_cf_node_prev(&loop->cf_node));
  83    nir_block *after = nir_cf_node_as_block(nir_cf_node_next(&loop->cf_node));
  84
  85    return block->index > before->index && block->index < after->index;
  86 }
  87
  88 /* Given the LCA of all uses and the definition, find a block on the path
  89  * between them in the dominance tree that is outside of as many loops as
  90  * possible.
  91  */
  92
  93 static nir_block *
  94 adjust_block_for_loops(nir_block *use_block, nir_block *def_block)
  95 {
  96    for (nir_block *cur_block = use_block; cur_block != def_block->imm_dom;
  97         cur_block = cur_block->imm_dom) {
  98       nir_cf_node *next = nir_cf_node_next(&cur_block->cf_node);
  99       if (next && next->type == nir_cf_node_loop) {
 100          nir_loop *following_loop = nir_cf_node_as_loop(next);
 101          if (loop_contains_block(following_loop, use_block)) {
 102              use_block = cur_block;
 103              continue;
 104          }
 105       }
 106    }
 107
 108    return use_block;
 109 }
 110
 111 /* iterate a ssa def's use's and try to find a more optimal block to
 112  * move it to, using the dominance tree.  In short, if all of the uses
 113  * are contained in a single block, the load will be moved there,
 114  * otherwise it will be move to the least common ancestor block of all
 115  * the uses
 116  */
 117 static nir_block *
 118 get_preferred_block(nir_ssa_def *def, bool sink_into_loops)
 119 {
 120    nir_block *lca = NULL;
 121
 122    nir_foreach_use(use, def) {
 123       nir_instr *instr = use->parent_instr;
 124       nir_block *use_block = instr->block;
 125
 126       /*
 127        * Kind of an ugly special-case, but phi instructions
 128        * need to appear first in the block, so by definition
 129        * we can't move an instruction into a block where it is
 130        * consumed by a phi instruction.  We could conceivably
 131        * move it into a dominator block.
 132        */
 133       if (instr->type == nir_instr_type_phi) {
 134          nir_phi_instr *phi = nir_instr_as_phi(instr);
 135          nir_block *phi_lca = NULL;
 136          nir_foreach_phi_src(src, phi) {
 137             if (&src->src == use)
 138                phi_lca = nir_dominance_lca(phi_lca, src->pred);
 139          }
 140          use_block = phi_lca;
 141       }
 142
 143       lca = nir_dominance_lca(lca, use_block);
 144    }
 145
 146    nir_foreach_if_use(use, def) {
 147       nir_block *use_block =
 148          nir_cf_node_as_block(nir_cf_node_prev(&use->parent_if->cf_node));
 149
 150       lca = nir_dominance_lca(lca, use_block);
 151    }
 152
 153    /* If we're moving a load_ubo or load_interpolated_input, we don't want to
 154     * sink it down into loops, which may result in accessing memory or shared
 155     * functions multiple times.  Sink it just above the start of the loop
 156     * where it's used.  For load_consts, undefs, and comparisons, we expect
 157     * the driver to be able to emit them as simple ALU ops, so sinking as far
 158     * in as we can go is probably worth it for register pressure.
 159     */
 160    if (!sink_into_loops) {
 161       lca = adjust_block_for_loops(lca, def->parent_instr->block);
 162       assert(nir_block_dominates(def->parent_instr->block, lca));
 163    }
 164
 165
 166    return lca;
 167 }
 168
 169 /* insert before first non-phi instruction: */
 170 static void
 171 insert_after_phi(nir_instr *instr, nir_block *block)
 172 {
 173    nir_foreach_instr(instr2, block) {
 174       if (instr2->type == nir_instr_type_phi)
 175          continue;
 176
 177       exec_node_insert_node_before(&instr2->node,
 178                                    &instr->node);
 179
 180       return;
 181    }
 182
 183    /* if haven't inserted it, push to tail (ie. empty block or possibly
 184     * a block only containing phi's?)
 185     */
 186    exec_list_push_tail(&block->instr_list, &instr->node);
 187 }
 188
 189 bool
 190 nir_opt_sink(nir_shader *shader, nir_move_options options)
 191 {
 192    bool progress = false;
 193
 194    nir_foreach_function(function, shader) {
 195       if (!function->impl)
 196          continue;
 197
 198       nir_metadata_require(function->impl,
 199                            nir_metadata_block_index | nir_metadata_dominance);
 200
 201       nir_foreach_block_reverse(block, function->impl) {
 202          nir_foreach_instr_reverse_safe(instr, block) {
 203             if (!nir_can_move_instr(instr, options))
 204                continue;
 205
 206             nir_ssa_def *def = nir_instr_ssa_def(instr);
 207             nir_block *use_block =
 208                   get_preferred_block(def, instr->type != nir_instr_type_intrinsic);
 209
 210             if (!use_block || use_block == instr->block)
 211                continue;
 212
 213             exec_node_remove(&instr->node);
 214
 215             insert_after_phi(instr, use_block);
 216
 217             instr->block = use_block;
 218
 219             progress = true;
 220          }
 221       }
 222
 223       nir_metadata_preserve(function->impl,
 224                             nir_metadata_block_index | nir_metadata_dominance);
 225    }
 226
 227    return progress;
 228 }