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  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)
  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.       variable_entry *entry = (variable_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.              !ir_has_call(entry->assign)) {
  83.             entry->assign->remove();
  84.             progress = true;
  85.  
  86.             if (debug) {
  87.                printf("Removed assignment to %s@%p\n",
  88.                       entry->var->name, (void *) entry->var);
  89.             }
  90.          }
  91.       } else {
  92.          /* If there are no assignments or references to the variable left,
  93.           * then we can remove its declaration.
  94.           */
  95.  
  96.          /* uniform initializers are precious, and could get used by another
  97.           * stage.
  98.           */
  99.          if (entry->var->mode == ir_var_uniform &&
  100.              entry->var->constant_value)
  101.             continue;
  102.  
  103.          entry->var->remove();
  104.          progress = true;
  105.  
  106.          if (debug) {
  107.             printf("Removed declaration of %s@%p\n",
  108.                    entry->var->name, (void *) entry->var);
  109.          }
  110.       }
  111.    }
  112.  
  113.    return progress;
  114. }
  115.  
  116. /**
  117.  * Does a dead code pass on the functions present in the instruction stream.
  118.  *
  119.  * This is suitable for use while the program is not linked, as it will
  120.  * ignore variable declarations (and the assignments to them) for variables
  121.  * with global scope.
  122.  */
  123. bool
  124. do_dead_code_unlinked(exec_list *instructions)
  125. {
  126.    bool progress = false;
  127.  
  128.    foreach_iter(exec_list_iterator, iter, *instructions) {
  129.       ir_instruction *ir = (ir_instruction *)iter.get();
  130.       ir_function *f = ir->as_function();
  131.       if (f) {
  132.          foreach_iter(exec_list_iterator, sigiter, *f) {
  133.             ir_function_signature *sig =
  134.                (ir_function_signature *) sigiter.get();
  135.             if (do_dead_code(&sig->body))
  136.                progress = true;
  137.          }
  138.       }
  139.    }
  140.  
  141.    return progress;
  142. }
  143.