src/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 "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       if (entry->assign) {
  79          /* Remove a single dead assignment to the variable we found.
  80           * Don't do so if it's a shader or function output, though.
  81           */
  82          if (entry->var->data.mode != ir_var_function_out &&
  83              entry->var->data.mode != ir_var_function_inout &&
  84              entry->var->data.mode != ir_var_shader_out) {
  85             entry->assign->remove();
  86             progress = true;
  87
  88             if (debug) {
  89                printf("Removed assignment to %s@%p\n",
  90                       entry->var->name, (void *) entry->var);
  91             }
  92          }
  93       } else {
  94          /* If there are no assignments or references to the variable left,
  95           * then we can remove its declaration.
  96           */
  97
  98          /* uniform initializers are precious, and could get used by another
  99           * stage.  Also, once uniform locations have been assigned, the
 100           * declaration cannot be deleted.
 101           */
 102          if (entry->var->data.mode == ir_var_uniform) {
 103             if (uniform_locations_assigned || entry->var->constant_value)
 104                continue;
 105
 106             /* Section 2.11.6 (Uniform Variables) of the OpenGL ES 3.0.3 spec
 107              * says:
 108              *
 109              *     "All members of a named uniform block declared with a
 110              *     shared or std140 layout qualifier are considered active,
 111              *     even if they are not referenced in any shader in the
 112              *     program. The uniform block itself is also considered
 113              *     active, even if no member of the block is referenced."
 114              *
 115              * If the variable is in a uniform block with one of those
 116              * layouts, do not eliminate it.
 117              */
 118             if (entry->var->is_in_uniform_block()) {
 119                const glsl_type *const block_type =
 120                   entry->var->is_interface_instance()
 121                   ? entry->var->type : entry->var->get_interface_type();
 122
 123                if (block_type->interface_packing != GLSL_INTERFACE_PACKING_PACKED)
 124                   continue;
 125             }
 126          }
 127
 128          entry->var->remove();
 129          progress = true;
 130
 131          if (debug) {
 132             printf("Removed declaration of %s@%p\n",
 133                    entry->var->name, (void *) entry->var);
 134          }
 135       }
 136    }
 137
 138    return progress;
 139 }
 140
 141 /**
 142  * Does a dead code pass on the functions present in the instruction stream.
 143  *
 144  * This is suitable for use while the program is not linked, as it will
 145  * ignore variable declarations (and the assignments to them) for variables
 146  * with global scope.
 147  */
 148 bool
 149 do_dead_code_unlinked(exec_list *instructions)
 150 {
 151    bool progress = false;
 152
 153    foreach_in_list(ir_instruction, ir, instructions) {
 154       ir_function *f = ir->as_function();
 155       if (f) {
 156          foreach_in_list(ir_function_signature, sig, &f->signatures) {
 157             /* The setting of the uniform_locations_assigned flag here is
 158              * irrelevent.  If there is a uniform declaration encountered
 159              * inside the body of the function, something has already gone
 160              * terribly, terribly wrong.
 161              */
 162             if (do_dead_code(&sig->body, false))
 163                progress = true;
 164          }
 165       }
 166    }
 167
 168    return progress;
 169 }