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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"
34 #include "main/hash_table.h"
36 static bool debug
= false;
39 * Do a dead code pass over instructions and everything that instructions
42 * Note that this will remove assignments to globals, so it is not suitable
43 * for usage on an unlinked instruction stream.
46 do_dead_code(exec_list
*instructions
, bool uniform_locations_assigned
)
48 ir_variable_refcount_visitor v
;
49 bool progress
= false;
54 hash_table_foreach(v
.ht
, e
) {
55 ir_variable_refcount_entry
*entry
= (ir_variable_refcount_entry
*)e
->data
;
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
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.
65 assert(entry
->referenced_count
>= entry
->assigned_count
);
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 ");
74 if ((entry
->referenced_count
> entry
->assigned_count
)
75 || !entry
->declaration
)
79 /* Remove a single dead assignment to the variable we found.
80 * Don't do so if it's a shader output, though.
82 if (entry
->var
->mode
!= ir_var_out
&&
83 entry
->var
->mode
!= ir_var_inout
) {
84 entry
->assign
->remove();
88 printf("Removed assignment to %s@%p\n",
89 entry
->var
->name
, (void *) entry
->var
);
93 /* If there are no assignments or references to the variable left,
94 * then we can remove its declaration.
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.
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.
105 if (entry
->var
->mode
== ir_var_uniform
&&
106 (uniform_locations_assigned
||
107 entry
->var
->constant_value
||
108 entry
->var
->uniform_block
!= -1))
111 entry
->var
->remove();
115 printf("Removed declaration of %s@%p\n",
116 entry
->var
->name
, (void *) entry
->var
);
125 * Does a dead code pass on the functions present in the instruction stream.
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
132 do_dead_code_unlinked(exec_list
*instructions
)
134 bool progress
= false;
136 foreach_iter(exec_list_iterator
, iter
, *instructions
) {
137 ir_instruction
*ir
= (ir_instruction
*)iter
.get();
138 ir_function
*f
= ir
->as_function();
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.
148 if (do_dead_code(&sig
->body
, false))