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25 * \file lower_instructions.cpp
27 * Many GPUs lack native instructions for certain expression operations, and
28 * must replace them with some other expression tree. This pass lowers some
29 * of the most common cases, allowing the lowering code to be implemented once
30 * rather than in each driver backend.
32 * Currently supported transformations:
35 * - INT_DIV_TO_MUL_RCP
43 * Breaks an ir_binop_sub expression down to add(op0, neg(op1))
45 * This simplifies expression reassociation, and for many backends
46 * there is no subtract operation separate from adding the negation.
47 * For backends with native subtract operations, they will probably
48 * want to recognize add(op0, neg(op1)) or the other way around to
49 * produce a subtract anyway.
51 * DIV_TO_MUL_RCP and INT_DIV_TO_MUL_RCP:
52 * --------------------------------------
53 * Breaks an ir_binop_div expression down to op0 * (rcp(op1)).
55 * Many GPUs don't have a divide instruction (945 and 965 included),
56 * but they do have an RCP instruction to compute an approximate
57 * reciprocal. By breaking the operation down, constant reciprocals
58 * can get constant folded.
60 * DIV_TO_MUL_RCP only lowers floating point division; INT_DIV_TO_MUL_RCP
61 * handles the integer case, converting to and from floating point so that
64 * EXP_TO_EXP2 and LOG_TO_LOG2:
65 * ----------------------------
66 * Many GPUs don't have a base e log or exponent instruction, but they
67 * do have base 2 versions, so this pass converts exp and log to exp2
68 * and log2 operations.
72 * Many older GPUs don't have an x**y instruction. For these GPUs, convert
73 * x**y to 2**(y * log2(x)).
77 * Breaks an ir_binop_mod expression down to (op1 * fract(op0 / op1))
79 * Many GPUs don't have a MOD instruction (945 and 965 included), and
80 * if we have to break it down like this anyway, it gives an
81 * opportunity to do things like constant fold the (1.0 / op1) easily.
84 #include "main/core.h" /* for M_LOG2E */
85 #include "glsl_types.h"
87 #include "ir_optimization.h"
89 class lower_instructions_visitor
: public ir_hierarchical_visitor
{
91 lower_instructions_visitor(unsigned lower
)
92 : progress(false), lower(lower
) { }
94 ir_visitor_status
visit_leave(ir_expression
*);
99 unsigned lower
; /** Bitfield of which operations to lower */
101 void sub_to_add_neg(ir_expression
*);
102 void div_to_mul_rcp(ir_expression
*);
103 void int_div_to_mul_rcp(ir_expression
*);
104 void mod_to_fract(ir_expression
*);
105 void exp_to_exp2(ir_expression
*);
106 void pow_to_exp2(ir_expression
*);
107 void log_to_log2(ir_expression
*);
111 * Determine if a particular type of lowering should occur
113 #define lowering(x) (this->lower & x)
116 lower_instructions(exec_list
*instructions
, unsigned what_to_lower
)
118 lower_instructions_visitor
v(what_to_lower
);
120 visit_list_elements(&v
, instructions
);
125 lower_instructions_visitor::sub_to_add_neg(ir_expression
*ir
)
127 ir
->operation
= ir_binop_add
;
128 ir
->operands
[1] = new(ir
) ir_expression(ir_unop_neg
, ir
->operands
[1]->type
,
129 ir
->operands
[1], NULL
);
130 this->progress
= true;
134 lower_instructions_visitor::div_to_mul_rcp(ir_expression
*ir
)
136 assert(ir
->operands
[1]->type
->is_float());
138 /* New expression for the 1.0 / op1 */
140 expr
= new(ir
) ir_expression(ir_unop_rcp
,
141 ir
->operands
[1]->type
,
144 /* op0 / op1 -> op0 * (1.0 / op1) */
145 ir
->operation
= ir_binop_mul
;
146 ir
->operands
[1] = expr
;
148 this->progress
= true;
152 lower_instructions_visitor::int_div_to_mul_rcp(ir_expression
*ir
)
154 assert(ir
->operands
[1]->type
->is_integer());
156 /* Be careful with integer division -- we need to do it as a
157 * float and re-truncate, since rcp(n > 1) of an integer would
160 ir_rvalue
*op0
, *op1
;
161 const struct glsl_type
*vec_type
;
163 vec_type
= glsl_type::get_instance(GLSL_TYPE_FLOAT
,
164 ir
->operands
[1]->type
->vector_elements
,
165 ir
->operands
[1]->type
->matrix_columns
);
167 if (ir
->operands
[1]->type
->base_type
== GLSL_TYPE_INT
)
168 op1
= new(ir
) ir_expression(ir_unop_i2f
, vec_type
, ir
->operands
[1], NULL
);
170 op1
= new(ir
) ir_expression(ir_unop_u2f
, vec_type
, ir
->operands
[1], NULL
);
172 op1
= new(ir
) ir_expression(ir_unop_rcp
, op1
->type
, op1
, NULL
);
174 vec_type
= glsl_type::get_instance(GLSL_TYPE_FLOAT
,
175 ir
->operands
[0]->type
->vector_elements
,
176 ir
->operands
[0]->type
->matrix_columns
);
178 if (ir
->operands
[0]->type
->base_type
== GLSL_TYPE_INT
)
179 op0
= new(ir
) ir_expression(ir_unop_i2f
, vec_type
, ir
->operands
[0], NULL
);
181 op0
= new(ir
) ir_expression(ir_unop_u2f
, vec_type
, ir
->operands
[0], NULL
);
183 vec_type
= glsl_type::get_instance(GLSL_TYPE_FLOAT
,
184 ir
->type
->vector_elements
,
185 ir
->type
->matrix_columns
);
187 op0
= new(ir
) ir_expression(ir_binop_mul
, vec_type
, op0
, op1
);
189 if (ir
->operands
[1]->type
->base_type
== GLSL_TYPE_INT
) {
190 ir
->operation
= ir_unop_f2i
;
191 ir
->operands
[0] = op0
;
193 ir
->operation
= ir_unop_i2u
;
194 ir
->operands
[0] = new(ir
) ir_expression(ir_unop_f2i
, op0
);
196 ir
->operands
[1] = NULL
;
198 this->progress
= true;
202 lower_instructions_visitor::exp_to_exp2(ir_expression
*ir
)
204 ir_constant
*log2_e
= new(ir
) ir_constant(float(M_LOG2E
));
206 ir
->operation
= ir_unop_exp2
;
207 ir
->operands
[0] = new(ir
) ir_expression(ir_binop_mul
, ir
->operands
[0]->type
,
208 ir
->operands
[0], log2_e
);
209 this->progress
= true;
213 lower_instructions_visitor::pow_to_exp2(ir_expression
*ir
)
215 ir_expression
*const log2_x
=
216 new(ir
) ir_expression(ir_unop_log2
, ir
->operands
[0]->type
,
219 ir
->operation
= ir_unop_exp2
;
220 ir
->operands
[0] = new(ir
) ir_expression(ir_binop_mul
, ir
->operands
[1]->type
,
221 ir
->operands
[1], log2_x
);
222 ir
->operands
[1] = NULL
;
223 this->progress
= true;
227 lower_instructions_visitor::log_to_log2(ir_expression
*ir
)
229 ir
->operation
= ir_binop_mul
;
230 ir
->operands
[0] = new(ir
) ir_expression(ir_unop_log2
, ir
->operands
[0]->type
,
231 ir
->operands
[0], NULL
);
232 ir
->operands
[1] = new(ir
) ir_constant(float(1.0 / M_LOG2E
));
233 this->progress
= true;
237 lower_instructions_visitor::mod_to_fract(ir_expression
*ir
)
239 ir_variable
*temp
= new(ir
) ir_variable(ir
->operands
[1]->type
, "mod_b",
241 this->base_ir
->insert_before(temp
);
243 ir_assignment
*const assign
=
244 new(ir
) ir_assignment(new(ir
) ir_dereference_variable(temp
),
245 ir
->operands
[1], NULL
);
247 this->base_ir
->insert_before(assign
);
249 ir_expression
*const div_expr
=
250 new(ir
) ir_expression(ir_binop_div
, ir
->operands
[0]->type
,
252 new(ir
) ir_dereference_variable(temp
));
254 /* Don't generate new IR that would need to be lowered in an additional
257 if (lowering(DIV_TO_MUL_RCP
))
258 div_to_mul_rcp(div_expr
);
260 ir_rvalue
*expr
= new(ir
) ir_expression(ir_unop_fract
,
261 ir
->operands
[0]->type
,
265 ir
->operation
= ir_binop_mul
;
266 ir
->operands
[0] = new(ir
) ir_dereference_variable(temp
);
267 ir
->operands
[1] = expr
;
268 this->progress
= true;
272 lower_instructions_visitor::visit_leave(ir_expression
*ir
)
274 switch (ir
->operation
) {
276 if (lowering(SUB_TO_ADD_NEG
))
281 if (ir
->operands
[1]->type
->is_integer() && lowering(INT_DIV_TO_MUL_RCP
))
282 int_div_to_mul_rcp(ir
);
283 else if (ir
->operands
[1]->type
->is_float() && lowering(DIV_TO_MUL_RCP
))
288 if (lowering(EXP_TO_EXP2
))
293 if (lowering(LOG_TO_LOG2
))
298 if (lowering(MOD_TO_FRACT
) && ir
->type
->is_float())
303 if (lowering(POW_TO_EXP2
))
308 return visit_continue
;
311 return visit_continue
;