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 "main/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 output, though.
  81           */
  82          if (entry->var->mode != ir_var_out &&
  83              entry->var->mode != ir_var_inout) {
  84             entry->assign->remove();
  85             progress = true;
  86
  87             if (debug) {
  88                printf("Removed assignment to %s@%p\n",
  89                       entry->var->name, (void *) entry->var);
  90             }
  91          }
  92       } else {
  93          /* If there are no assignments or references to the variable left,
  94           * then we can remove its declaration.
  95           */
  96
  97          /* uniform initializers are precious, and could get used by another
  98           * stage.  Also, once uniform locations have been assigned, the
  99           * declaration cannot be deleted.
 100           *
 101           * Also, GL_ARB_uniform_buffer_object says that std140
 102           * uniforms will not be eliminated.  Since we always do
 103           * std140, just don't eliminate uniforms in UBOs.
 104           */
 105          if (entry->var->mode == ir_var_uniform &&
 106              (uniform_locations_assigned ||
 107               entry->var->constant_value ||
 108               entry->var->uniform_block != -1))
 109             continue;
 110
 111          entry->var->remove();
 112          progress = true;
 113
 114          if (debug) {
 115             printf("Removed declaration of %s@%p\n",
 116                    entry->var->name, (void *) entry->var);
 117          }
 118       }
 119    }
 120
 121    return progress;
 122 }
 123
 124 /**
 125  * Does a dead code pass on the functions present in the instruction stream.
 126  *
 127  * This is suitable for use while the program is not linked, as it will
 128  * ignore variable declarations (and the assignments to them) for variables
 129  * with global scope.
 130  */
 131 bool
 132 do_dead_code_unlinked(exec_list *instructions)
 133 {
 134    bool progress = false;
 135
 136    foreach_iter(exec_list_iterator, iter, *instructions) {
 137       ir_instruction *ir = (ir_instruction *)iter.get();
 138       ir_function *f = ir->as_function();
 139       if (f) {
 140          foreach_iter(exec_list_iterator, sigiter, *f) {
 141             ir_function_signature *sig =
 142                (ir_function_signature *) sigiter.get();
 143             /* The setting of the uniform_locations_assigned flag here is
 144              * irrelevent.  If there is a uniform declaration encountered
 145              * inside the body of the function, something has already gone
 146              * terribly, terribly wrong.
 147              */
 148             if (do_dead_code(&sig->body, false))
 149                progress = true;
 150          }
 151       }
 152    }
 153
 154    return progress;
 155 }