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