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
  35 static bool debug = false;
  36
  37 /**
  38  * Do a dead code pass over instructions and everything that instructions
  39  * references.
  40  *
  41  * Note that this will remove assignments to globals, so it is not suitable
  42  * for usage on an unlinked instruction stream.
  43  */
  44 bool
  45 do_dead_code(exec_list *instructions, bool uniform_locations_assigned)
  46 {
  47    ir_variable_refcount_visitor v;
  48    bool progress = false;
  49
  50    v.run(instructions);
  51
  52    foreach_iter(exec_list_iterator, iter, v.variable_list) {
  53       ir_variable_refcount_entry *entry = (ir_variable_refcount_entry *)iter.get();
  54
  55       /* Since each assignment is a reference, the refereneced count must be
  56        * greater than or equal to the assignment count.  If they are equal,
  57        * then all of the references are assignments, and the variable is
  58        * dead.
  59        *
  60        * Note that if the variable is neither assigned nor referenced, both
  61        * counts will be zero and will be caught by the equality test.
  62        */
  63       assert(entry->referenced_count >= entry->assigned_count);
  64
  65       if (debug) {
  66          printf("%s@%p: %d refs, %d assigns, %sdeclared in our scope\n",
  67                 entry->var->name, (void *) entry->var,
  68                 entry->referenced_count, entry->assigned_count,
  69                 entry->declaration ? "" : "not ");
  70       }
  71
  72       if ((entry->referenced_count > entry->assigned_count)
  73           || !entry->declaration)
  74          continue;
  75
  76       if (entry->assign) {
  77          /* Remove a single dead assignment to the variable we found.
  78           * Don't do so if it's a shader output, though.
  79           */
  80          if (entry->var->mode != ir_var_out &&
  81              entry->var->mode != ir_var_inout) {
  82             entry->assign->remove();
  83             progress = true;
  84
  85             if (debug) {
  86                printf("Removed assignment to %s@%p\n",
  87                       entry->var->name, (void *) entry->var);
  88             }
  89          }
  90       } else {
  91          /* If there are no assignments or references to the variable left,
  92           * then we can remove its declaration.
  93           */
  94
  95          /* uniform initializers are precious, and could get used by another
  96           * stage.  Also, once uniform locations have been assigned, the
  97           * declaration cannot be deleted.
  98           *
  99           * Also, GL_ARB_uniform_buffer_object says that std140
 100           * uniforms will not be eliminated.  Since we always do
 101           * std140, just don't eliminate uniforms in UBOs.
 102           */
 103          if (entry->var->mode == ir_var_uniform &&
 104              (uniform_locations_assigned ||
 105               entry->var->constant_value ||
 106               entry->var->uniform_block != -1))
 107             continue;
 108
 109          entry->var->remove();
 110          progress = true;
 111
 112          if (debug) {
 113             printf("Removed declaration of %s@%p\n",
 114                    entry->var->name, (void *) entry->var);
 115          }
 116       }
 117    }
 118
 119    return progress;
 120 }
 121
 122 /**
 123  * Does a dead code pass on the functions present in the instruction stream.
 124  *
 125  * This is suitable for use while the program is not linked, as it will
 126  * ignore variable declarations (and the assignments to them) for variables
 127  * with global scope.
 128  */
 129 bool
 130 do_dead_code_unlinked(exec_list *instructions)
 131 {
 132    bool progress = false;
 133
 134    foreach_iter(exec_list_iterator, iter, *instructions) {
 135       ir_instruction *ir = (ir_instruction *)iter.get();
 136       ir_function *f = ir->as_function();
 137       if (f) {
 138          foreach_iter(exec_list_iterator, sigiter, *f) {
 139             ir_function_signature *sig =
 140                (ir_function_signature *) sigiter.get();
 141             /* The setting of the uniform_locations_assigned flag here is
 142              * irrelevent.  If there is a uniform declaration encountered
 143              * inside the body of the function, something has already gone
 144              * terribly, terribly wrong.
 145              */
 146             if (do_dead_code(&sig->body, false))
 147                progress = true;
 148          }
 149       }
 150    }
 151
 152    return progress;
 153 }