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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 "util/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 or function output or a shader
81 * storage variable though.
83 if (entry
->var
->data
.mode
!= ir_var_function_out
&&
84 entry
->var
->data
.mode
!= ir_var_function_inout
&&
85 entry
->var
->data
.mode
!= ir_var_shader_out
&&
86 entry
->var
->data
.mode
!= ir_var_shader_storage
) {
87 entry
->assign
->remove();
91 printf("Removed assignment to %s@%p\n",
92 entry
->var
->name
, (void *) entry
->var
);
96 /* If there are no assignments or references to the variable left,
97 * then we can remove its declaration.
100 /* uniform initializers are precious, and could get used by another
101 * stage. Also, once uniform locations have been assigned, the
102 * declaration cannot be deleted.
104 if (entry
->var
->data
.mode
== ir_var_uniform
||
105 entry
->var
->data
.mode
== ir_var_shader_storage
) {
106 if (uniform_locations_assigned
|| entry
->var
->constant_value
)
109 /* Section 2.11.6 (Uniform Variables) of the OpenGL ES 3.0.3 spec
112 * "All members of a named uniform block declared with a
113 * shared or std140 layout qualifier are considered active,
114 * even if they are not referenced in any shader in the
115 * program. The uniform block itself is also considered
116 * active, even if no member of the block is referenced."
118 * If the variable is in a uniform block with one of those
119 * layouts, do not eliminate it.
121 if (entry
->var
->is_in_buffer_block()) {
122 const glsl_type
*const block_type
=
123 entry
->var
->is_interface_instance()
124 ? entry
->var
->type
: entry
->var
->get_interface_type();
126 if (block_type
->interface_packing
!= GLSL_INTERFACE_PACKING_PACKED
)
131 entry
->var
->remove();
135 printf("Removed declaration of %s@%p\n",
136 entry
->var
->name
, (void *) entry
->var
);
145 * Does a dead code pass on the functions present in the instruction stream.
147 * This is suitable for use while the program is not linked, as it will
148 * ignore variable declarations (and the assignments to them) for variables
152 do_dead_code_unlinked(exec_list
*instructions
)
154 bool progress
= false;
156 foreach_in_list(ir_instruction
, ir
, instructions
) {
157 ir_function
*f
= ir
->as_function();
159 foreach_in_list(ir_function_signature
, sig
, &f
->signatures
) {
160 /* The setting of the uniform_locations_assigned flag here is
161 * irrelevent. If there is a uniform declaration encountered
162 * inside the body of the function, something has already gone
163 * terribly, terribly wrong.
165 if (do_dead_code(&sig
->body
, false))