src/compiler/nir/nir_phi_builder.h

   1 /*
   2  * Copyright © 2016 Intel Corporation
   3  *
   4  * Permission is hereby granted, free of charge, to any person obtaining a
   5  * copy of this software and associated documentation files (the "Software"),
   6  * to deal in the Software without restriction, including without limitation
   7  * the rights to use, copy, modify, merge, publish, distribute, sublicense,
   8  * and/or sell copies of the Software, and to permit persons to whom the
   9  * Software is furnished to do so, subject to the following conditions:
  10  *
  11  * The above copyright notice and this permission notice (including the next
  12  * paragraph) shall be included in all copies or substantial portions of the
  13  * Software.
  14  *
  15  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  16  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  17  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
  18  * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  19  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
  20  * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
  21  * IN THE SOFTWARE.
  22  */
  23
  24 #pragma once
  25
  26 #include "nir.h"
  27
  28 /** A helper for placing phi nodes in a NIR shader
  29  *
  30  * Basic usage goes something like this:
  31  *
  32  *     each variable, var, has:
  33  *         a bitset var.defs of blocks where the variable is defined
  34  *         a struct nir_phi_builder_value *pb_val
  35  *
  36  *     // initialize bitsets
  37  *     foreach block:
  38  *         foreach def of variable var:
  39  *             var.defs[def.block] = true;
  40  *
  41  *     // initialize phi builder
  42  *     pb = nir_phi_builder_create()
  43  *     foreach var:
  44  *         var.pb_val = nir_phi_builder_add_value(pb, var.defs)
  45  *
  46  *     // Visit each block.  This needs to visit dominators first;
  47  *     // nir_for_each_block() will be ok.
  48  *     foreach block:
  49  *         foreach instruction:
  50  *             foreach use of variable var:
  51  *                 replace use with nir_phi_builder_get_block_def(var.pb_val)
  52  *             foreach def of variable var:
  53  *                 create ssa def, register with
  54  *     nir_phi_builder_set_block_def(var.pb_val)
  55  *
  56  *     nir_phi_builder_finish(pb)
  57  */
  58 struct nir_phi_builder;
  59
  60 struct nir_phi_builder_value;
  61
  62 /* Create a new phi builder.
  63  *
  64  * While this is fairly cheap, it does allocate some memory and walk the list
  65  * of blocks so it's recommended that you only call it once and use it to
  66  * build phis for several values.
  67  */
  68 struct nir_phi_builder *nir_phi_builder_create(nir_function_impl *impl);
  69
  70 /* Register a value with the builder.
  71  *
  72  * The 'defs' parameter specifies a bitset of blocks in which the given value
  73  * is defined.  This is used to determine where to place the phi nodes.
  74  */
  75 struct nir_phi_builder_value *
  76 nir_phi_builder_add_value(struct nir_phi_builder *pb, unsigned num_components,
  77                           unsigned bit_size, const BITSET_WORD *defs);
  78
  79 /* Register a definition for the given value and block.
  80  *
  81  * It is safe to call this function as many times as you wish for any given
  82  * block/value pair.  However, it always replaces whatever was there
  83  * previously even if that definition is from a phi node.  The phi builder
  84  * always uses the latest information it has, so you must be careful about the
  85  * order in which you register definitions.  The final value at the end of the
  86  * block must be the last value registered.
  87  */
  88 void
  89 nir_phi_builder_value_set_block_def(struct nir_phi_builder_value *val,
  90                                     nir_block *block, nir_ssa_def *def);
  91
  92 /* Get the definition for the given value in the given block.
  93  *
  94  * This definition will always be the latest definition known for the given
  95  * block.  If no definition is immediately available, it will crawl up the
  96  * dominance tree and insert phi nodes as needed until it finds one.  In the
  97  * case that no suitable definition is found, it will return the result of a
  98  * nir_ssa_undef_instr with the correct number of components.
  99  *
 100  * Because this function only uses the latest available information for any
 101  * given block, you must have already finished registering definitions for any
 102  * blocks that dominate the current block in order to get the correct result.
 103  */
 104 nir_ssa_def *
 105 nir_phi_builder_value_get_block_def(struct nir_phi_builder_value *val,
 106                                     nir_block *block);
 107
 108 /* Finish building phi nodes and free the builder.
 109  *
 110  * This function does far more than just free memory.  Prior to calling
 111  * nir_phi_builder_finish, no phi nodes have actually been inserted in the
 112  * program.  This function is what finishes setting up phi node sources and
 113  * adds the phi nodes to the program.
 114  */
 115 void nir_phi_builder_finish(struct nir_phi_builder *pb);