src/compiler/glsl/opt_dead_code.cpp

   1 /*
   2  * Copyright © 2010 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
  21  * DEALINGS IN THE SOFTWARE.
  22  */
  23
  24 /**
  25  * \file opt_dead_code.cpp
  26  *
  27  * Eliminates dead assignments and variable declarations from the code.
  28  */
  29
  30 #include "ir.h"
  31 #include "ir_visitor.h"
  32 #include "ir_variable_refcount.h"
  33 #include "compiler/glsl_types.h"
  34 #include "util/hash_table.h"
  35
  36 static bool debug = false;
  37
  38 /**
  39  * Do a dead code pass over instructions and everything that instructions
  40  * references.
  41  *
  42  * Note that this will remove assignments to globals, so it is not suitable
  43  * for usage on an unlinked instruction stream.
  44  */
  45 bool
  46 do_dead_code(exec_list *instructions, bool uniform_locations_assigned)
  47 {
  48    ir_variable_refcount_visitor v;
  49    bool progress = false;
  50
  51    v.run(instructions);
  52
  53    hash_table_foreach(v.ht, e) {
  54       ir_variable_refcount_entry *entry = (ir_variable_refcount_entry *)e->data;
  55
  56       /* Since each assignment is a reference, the refereneced count must be
  57        * greater than or equal to the assignment count.  If they are equal,
  58        * then all of the references are assignments, and the variable is
  59        * dead.
  60        *
  61        * Note that if the variable is neither assigned nor referenced, both
  62        * counts will be zero and will be caught by the equality test.
  63        */
  64       assert(entry->referenced_count >= entry->assigned_count);
  65
  66       if (debug) {
  67          printf("%s@%p: %d refs, %d assigns, %sdeclared in our scope\n",
  68                 entry->var->name, (void *) entry->var,
  69                 entry->referenced_count, entry->assigned_count,
  70                 entry->declaration ? "" : "not ");
  71       }
  72
  73       if ((entry->referenced_count > entry->assigned_count)
  74           || !entry->declaration)
  75          continue;
  76
  77       /* Section 7.4.1 (Shader Interface Matching) of the OpenGL 4.5
  78        * (Core Profile) spec says:
  79        *
  80        *    "With separable program objects, interfaces between shader
  81        *    stages may involve the outputs from one program object and the
  82        *    inputs from a second program object.  For such interfaces, it is
  83        *    not possible to detect mismatches at link time, because the
  84        *    programs are linked separately. When each such program is
  85        *    linked, all inputs or outputs interfacing with another program
  86        *    stage are treated as active."
  87        */
  88       if (entry->var->data.always_active_io)
  89          continue;
  90
  91       if (!entry->assign_list.is_empty()) {
  92          /* Remove all the dead assignments to the variable we found.
  93           * Don't do so if it's a shader or function output, though.
  94           */
  95          if (entry->var->data.mode != ir_var_function_out &&
  96              entry->var->data.mode != ir_var_function_inout &&
  97              entry->var->data.mode != ir_var_shader_out &&
  98              entry->var->data.mode != ir_var_shader_storage) {
  99
 100             while (!entry->assign_list.is_empty()) {
 101                struct assignment_entry *assignment_entry =
 102                   exec_node_data(struct assignment_entry,
 103                                  entry->assign_list.get_head_raw(), link);
 104
 105                assignment_entry->assign->remove();
 106
 107                if (debug) {
 108                   printf("Removed assignment to %s@%p\n",
 109                          entry->var->name, (void *) entry->var);
 110                }
 111
 112                assignment_entry->link.remove();
 113                free(assignment_entry);
 114             }
 115             progress = true;
 116          }
 117       }
 118
 119       if (entry->assign_list.is_empty()) {
 120          /* If there are no assignments or references to the variable left,
 121           * then we can remove its declaration.
 122           */
 123
 124          /* uniform initializers are precious, and could get used by another
 125           * stage.  Also, once uniform locations have been assigned, the
 126           * declaration cannot be deleted.
 127           */
 128          if (entry->var->data.mode == ir_var_uniform ||
 129              entry->var->data.mode == ir_var_shader_storage) {
 130             if (uniform_locations_assigned || entry->var->constant_initializer)
 131                continue;
 132
 133             /* Section 2.11.6 (Uniform Variables) of the OpenGL ES 3.0.3 spec
 134              * says:
 135              *
 136              *     "All members of a named uniform block declared with a
 137              *     shared or std140 layout qualifier are considered active,
 138              *     even if they are not referenced in any shader in the
 139              *     program. The uniform block itself is also considered
 140              *     active, even if no member of the block is referenced."
 141              *
 142              * If the variable is in a uniform block with one of those
 143              * layouts, do not eliminate it.
 144              */
 145             if (entry->var->is_in_buffer_block()) {
 146                if (entry->var->get_interface_type_packing() !=
 147                    GLSL_INTERFACE_PACKING_PACKED) {
 148                   /* Set used to false so it doesn't get set as referenced by
 149                    * the shader in the program resource list. This will also
 150                    * help avoid the state being unnecessarily flushed for the
 151                    * shader stage.
 152                    */
 153                   entry->var->data.used = false;
 154                   continue;
 155                }
 156             }
 157
 158             if (entry->var->type->is_subroutine())
 159                continue;
 160          }
 161
 162          entry->var->remove();
 163          progress = true;
 164
 165          if (debug) {
 166             printf("Removed declaration of %s@%p\n",
 167                    entry->var->name, (void *) entry->var);
 168          }
 169       }
 170    }
 171
 172    return progress;
 173 }
 174
 175 /**
 176  * Does a dead code pass on the functions present in the instruction stream.
 177  *
 178  * This is suitable for use while the program is not linked, as it will
 179  * ignore variable declarations (and the assignments to them) for variables
 180  * with global scope.
 181  */
 182 bool
 183 do_dead_code_unlinked(exec_list *instructions)
 184 {
 185    bool progress = false;
 186
 187    foreach_in_list(ir_instruction, ir, instructions) {
 188       ir_function *f = ir->as_function();
 189       if (f) {
 190          foreach_in_list(ir_function_signature, sig, &f->signatures) {
 191             /* The setting of the uniform_locations_assigned flag here is
 192              * irrelevent.  If there is a uniform declaration encountered
 193              * inside the body of the function, something has already gone
 194              * terribly, terribly wrong.
 195              */
 196             if (do_dead_code(&sig->body, false))
 197                progress = true;
 198          }
 199       }
 200    }
 201
 202    return progress;
 203 }