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25 * \file opt_dead_code.cpp
27 * Eliminates dead assignments and variable declarations from the code.
31 #include "ir_visitor.h"
32 #include "ir_variable_refcount.h"
33 #include "glsl_types.h"
35 static bool debug = false;
38 * Do a dead code pass over instructions and everything that instructions
41 * Note that this will remove assignments to globals, so it is not suitable
42 * for usage on an unlinked instruction stream.
45 do_dead_code(exec_list *instructions, bool uniform_locations_assigned)
47 ir_variable_refcount_visitor v;
48 bool progress = false;
52 foreach_iter(exec_list_iterator, iter, v.variable_list) {
53 ir_variable_refcount_entry *entry = (ir_variable_refcount_entry *)iter.get();
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
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.
63 assert(entry->referenced_count >= entry->assigned_count);
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 ");
72 if ((entry->referenced_count > entry->assigned_count)
73 || !entry->declaration)
77 /* Remove a single dead assignment to the variable we found.
78 * Don't do so if it's a shader output, though.
80 if (entry->var->mode != ir_var_out &&
81 entry->var->mode != ir_var_inout) {
82 entry->assign->remove();
86 printf("Removed assignment to %s@%p\n",
87 entry->var->name, (void *) entry->var);
91 /* If there are no assignments or references to the variable left,
92 * then we can remove its declaration.
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.
99 if (entry->var->mode == ir_var_uniform &&
100 (uniform_locations_assigned || entry->var->constant_value))
103 entry->var->remove();
107 printf("Removed declaration of %s@%p\n",
108 entry->var->name, (void *) entry->var);
117 * Does a dead code pass on the functions present in the instruction stream.
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
124 do_dead_code_unlinked(exec_list *instructions)
126 bool progress = false;
128 foreach_iter(exec_list_iterator, iter, *instructions) {
129 ir_instruction *ir = (ir_instruction *)iter.get();
130 ir_function *f = ir->as_function();
132 foreach_iter(exec_list_iterator, sigiter, *f) {
133 ir_function_signature *sig =
134 (ir_function_signature *) sigiter.get();
135 /* The setting of the uniform_locations_assigned flag here is
136 * irrelevent. If there is a uniform declaration encountered
137 * inside the body of the function, something has already gone
138 * terribly, terribly wrong.
140 if (do_dead_code(&sig->body, false))