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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  * constant 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, constant, 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 constantright 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 CONSTANTRIGHT 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_constant_propagation.cpp
26  *
27  * Tracks assignments of constants to channels of variables, and
28  * usage of those constant channels with direct usage of the constants.
29  *
30  * This can lead to constant folding and algebraic optimizations in
31  * those later expressions, while causing no increase in instruction
32  * count (due to constants being generally free to load from a
33  * constant push buffer or as instruction immediate values) and
34  * possibly reducing register pressure.
35  */
36 
37 #include "ir.h"
38 #include "ir_visitor.h"
39 #include "ir_rvalue_visitor.h"
40 #include "ir_basic_block.h"
41 #include "ir_optimization.h"
42 #include "glsl_types.h"
43 
44 class acp_entry : public exec_node
45 {
46 public:
acp_entry(ir_variable * var,unsigned write_mask,ir_constant * constant)47    acp_entry(ir_variable *var, unsigned write_mask, ir_constant *constant)
48    {
49       assert(var);
50       assert(constant);
51       this->var = var;
52       this->write_mask = write_mask;
53       this->constant = constant;
54    }
55 
56    ir_variable *var;
57    ir_constant *constant;
58    unsigned write_mask;
59 };
60 
61 
62 class kill_entry : public exec_node
63 {
64 public:
kill_entry(ir_variable * var,unsigned write_mask)65    kill_entry(ir_variable *var, unsigned write_mask)
66    {
67       assert(var);
68       this->var = var;
69       this->write_mask = write_mask;
70    }
71 
72    ir_variable *var;
73    unsigned write_mask;
74 };
75 
76 class ir_constant_propagation_visitor : public ir_rvalue_visitor {
77 public:
ir_constant_propagation_visitor()78    ir_constant_propagation_visitor()
79    {
80       progress = false;
81       mem_ctx = hieralloc_new(0);
82       this->acp = new(mem_ctx) exec_list;
83       this->kills = new(mem_ctx) exec_list;
84    }
~ir_constant_propagation_visitor()85    ~ir_constant_propagation_visitor()
86    {
87       hieralloc_free(mem_ctx);
88    }
89 
90    virtual ir_visitor_status visit_enter(class ir_loop *);
91    virtual ir_visitor_status visit_enter(class ir_function_signature *);
92    virtual ir_visitor_status visit_enter(class ir_function *);
93    virtual ir_visitor_status visit_leave(class ir_assignment *);
94    virtual ir_visitor_status visit_enter(class ir_call *);
95    virtual ir_visitor_status visit_enter(class ir_if *);
96 
97    void add_constant(ir_assignment *ir);
98    void kill(ir_variable *ir, unsigned write_mask);
99    void handle_if_block(exec_list *instructions);
100    void handle_rvalue(ir_rvalue **rvalue);
101 
102    /** List of acp_entry: The available constants to propagate */
103    exec_list *acp;
104 
105    /**
106     * List of kill_entry: The masks of variables whose values were
107     * killed in this block.
108     */
109    exec_list *kills;
110 
111    bool progress;
112 
113    bool killed_all;
114 
115    void *mem_ctx;
116 };
117 
118 
119 void
handle_rvalue(ir_rvalue ** rvalue)120 ir_constant_propagation_visitor::handle_rvalue(ir_rvalue **rvalue)
121 {
122    if (this->in_assignee || !*rvalue)
123       return;
124 
125    const glsl_type *type = (*rvalue)->type;
126    if (!type->is_scalar() && !type->is_vector())
127       return;
128 
129    ir_swizzle *swiz = NULL;
130    ir_dereference_variable *deref = (*rvalue)->as_dereference_variable();
131    if (!deref) {
132       swiz = (*rvalue)->as_swizzle();
133       if (!swiz)
134 	 return;
135 
136       deref = swiz->val->as_dereference_variable();
137       if (!deref)
138 	 return;
139    }
140 
141    ir_constant_data data;
142    memset(&data, 0, sizeof(data));
143 
144    for (unsigned int i = 0; i < type->components(); i++) {
145       int channel;
146       acp_entry *found = NULL;
147 
148       if (swiz) {
149 	 switch (i) {
150 	 case 0: channel = swiz->mask.x; break;
151 	 case 1: channel = swiz->mask.y; break;
152 	 case 2: channel = swiz->mask.z; break;
153 	 case 3: channel = swiz->mask.w; break;
154 	 default: assert(!"shouldn't be reached"); channel = 0; break;
155 	 }
156       } else {
157 	 channel = i;
158       }
159 
160       foreach_iter(exec_list_iterator, iter, *this->acp) {
161 	 acp_entry *entry = (acp_entry *)iter.get();
162 	 if (entry->var == deref->var && entry->write_mask & (1 << channel)) {
163 	    found = entry;
164 	    break;
165 	 }
166       }
167 
168       if (!found)
169 	 return;
170 
171       int rhs_channel = 0;
172       for (int j = 0; j < 4; j++) {
173 	 if (j == channel)
174 	    break;
175 	 if (found->write_mask & (1 << j))
176 	    rhs_channel++;
177       }
178 
179       switch (type->base_type) {
180       case GLSL_TYPE_FLOAT:
181 	 data.f[i] = found->constant->value.f[rhs_channel];
182 	 break;
183       case GLSL_TYPE_INT:
184 	 data.i[i] = found->constant->value.i[rhs_channel];
185 	 break;
186       case GLSL_TYPE_UINT:
187 	 data.u[i] = found->constant->value.u[rhs_channel];
188 	 break;
189       case GLSL_TYPE_BOOL:
190 	 data.b[i] = found->constant->value.b[rhs_channel];
191 	 break;
192       default:
193 	 assert(!"not reached");
194 	 break;
195       }
196    }
197 
198    *rvalue = new(hieralloc_parent(deref)) ir_constant(type, &data);
199    this->progress = true;
200 }
201 
202 ir_visitor_status
visit_enter(ir_function_signature * ir)203 ir_constant_propagation_visitor::visit_enter(ir_function_signature *ir)
204 {
205    /* Treat entry into a function signature as a completely separate
206     * block.  Any instructions at global scope will be shuffled into
207     * main() at link time, so they're irrelevant to us.
208     */
209    exec_list *orig_acp = this->acp;
210    exec_list *orig_kills = this->kills;
211    bool orig_killed_all = this->killed_all;
212 
213    this->acp = new(mem_ctx) exec_list;
214    this->kills = new(mem_ctx) exec_list;
215    this->killed_all = false;
216 
217    visit_list_elements(this, &ir->body);
218 
219    this->kills = orig_kills;
220    this->acp = orig_acp;
221    this->killed_all = orig_killed_all;
222 
223    return visit_continue_with_parent;
224 }
225 
226 ir_visitor_status
visit_leave(ir_assignment * ir)227 ir_constant_propagation_visitor::visit_leave(ir_assignment *ir)
228 {
229    if (this->in_assignee)
230       return visit_continue;
231 
232    kill(ir->lhs->variable_referenced(), ir->write_mask);
233 
234    add_constant(ir);
235 
236    return visit_continue;
237 }
238 
239 ir_visitor_status
visit_enter(ir_function * ir)240 ir_constant_propagation_visitor::visit_enter(ir_function *ir)
241 {
242    (void) ir;
243    return visit_continue;
244 }
245 
246 ir_visitor_status
visit_enter(ir_call * ir)247 ir_constant_propagation_visitor::visit_enter(ir_call *ir)
248 {
249    /* Do constant propagation on call parameters, but skip any out params */
250    exec_list_iterator sig_param_iter = ir->get_callee()->parameters.iterator();
251    foreach_iter(exec_list_iterator, iter, ir->actual_parameters) {
252       ir_variable *sig_param = (ir_variable *)sig_param_iter.get();
253       ir_rvalue *param = (ir_rvalue *)iter.get();
254       if (sig_param->mode != ir_var_out && sig_param->mode != ir_var_inout) {
255 	 ir_rvalue *new_param = param;
256 	 handle_rvalue(&new_param);
257          if (new_param != param)
258 	    param->replace_with(new_param);
259 	 else
260 	    param->accept(this);
261       }
262       sig_param_iter.next();
263    }
264 
265    /* Since we're unlinked, we don't (necssarily) know the side effects of
266     * this call.  So kill all copies.
267     */
268    acp->make_empty();
269    this->killed_all = true;
270 
271    return visit_continue_with_parent;
272 }
273 
274 void
handle_if_block(exec_list * instructions)275 ir_constant_propagation_visitor::handle_if_block(exec_list *instructions)
276 {
277    exec_list *orig_acp = this->acp;
278    exec_list *orig_kills = this->kills;
279    bool orig_killed_all = this->killed_all;
280 
281    this->acp = new(mem_ctx) exec_list;
282    this->kills = new(mem_ctx) exec_list;
283    this->killed_all = false;
284 
285    /* Populate the initial acp with a constant of the original */
286    foreach_iter(exec_list_iterator, iter, *orig_acp) {
287       acp_entry *a = (acp_entry *)iter.get();
288       this->acp->push_tail(new(this->mem_ctx) acp_entry(a->var, a->write_mask,
289 							a->constant));
290    }
291 
292    visit_list_elements(this, instructions);
293 
294    if (this->killed_all) {
295       orig_acp->make_empty();
296    }
297 
298    exec_list *new_kills = this->kills;
299    this->kills = orig_kills;
300    this->acp = orig_acp;
301    this->killed_all = this->killed_all || orig_killed_all;
302 
303    foreach_iter(exec_list_iterator, iter, *new_kills) {
304       kill_entry *k = (kill_entry *)iter.get();
305       kill(k->var, k->write_mask);
306    }
307 }
308 
309 ir_visitor_status
visit_enter(ir_if * ir)310 ir_constant_propagation_visitor::visit_enter(ir_if *ir)
311 {
312    ir->condition->accept(this);
313    handle_rvalue(&ir->condition);
314 
315    handle_if_block(&ir->then_instructions);
316    handle_if_block(&ir->else_instructions);
317 
318    /* handle_if_block() already descended into the children. */
319    return visit_continue_with_parent;
320 }
321 
322 ir_visitor_status
visit_enter(ir_loop * ir)323 ir_constant_propagation_visitor::visit_enter(ir_loop *ir)
324 {
325    exec_list *orig_acp = this->acp;
326    exec_list *orig_kills = this->kills;
327    bool orig_killed_all = this->killed_all;
328 
329    /* FINISHME: For now, the initial acp for loops is totally empty.
330     * We could go through once, then go through again with the acp
331     * cloned minus the killed entries after the first run through.
332     */
333    this->acp = new(mem_ctx) exec_list;
334    this->kills = new(mem_ctx) exec_list;
335    this->killed_all = false;
336 
337    visit_list_elements(this, &ir->body_instructions);
338 
339    if (this->killed_all) {
340       orig_acp->make_empty();
341    }
342 
343    exec_list *new_kills = this->kills;
344    this->kills = orig_kills;
345    this->acp = orig_acp;
346    this->killed_all = this->killed_all || orig_killed_all;
347 
348    foreach_iter(exec_list_iterator, iter, *new_kills) {
349       kill_entry *k = (kill_entry *)iter.get();
350       kill(k->var, k->write_mask);
351    }
352 
353    /* already descended into the children. */
354    return visit_continue_with_parent;
355 }
356 
357 void
kill(ir_variable * var,unsigned write_mask)358 ir_constant_propagation_visitor::kill(ir_variable *var, unsigned write_mask)
359 {
360    assert(var != NULL);
361 
362    /* We don't track non-vectors. */
363    if (!var->type->is_vector() && !var->type->is_scalar())
364       return;
365 
366    /* Remove any entries currently in the ACP for this kill. */
367    foreach_iter(exec_list_iterator, iter, *this->acp) {
368       acp_entry *entry = (acp_entry *)iter.get();
369 
370       if (entry->var == var) {
371 	 entry->write_mask &= ~write_mask;
372 	 if (entry->write_mask == 0)
373 	    entry->remove();
374       }
375    }
376 
377    /* Add this writemask of the variable to the list of killed
378     * variables in this block.
379     */
380    foreach_iter(exec_list_iterator, iter, *this->kills) {
381       kill_entry *entry = (kill_entry *)iter.get();
382 
383       if (entry->var == var) {
384 	 entry->write_mask |= write_mask;
385 	 return;
386       }
387    }
388    /* Not already in the list.  Make new entry. */
389    this->kills->push_tail(new(this->mem_ctx) kill_entry(var, write_mask));
390 }
391 
392 /**
393  * Adds an entry to the available constant list if it's a plain assignment
394  * of a variable to a variable.
395  */
396 void
add_constant(ir_assignment * ir)397 ir_constant_propagation_visitor::add_constant(ir_assignment *ir)
398 {
399    acp_entry *entry;
400 
401    if (ir->condition) {
402       ir_constant *condition = ir->condition->as_constant();
403       if (!condition || !condition->value.b[0])
404 	 return;
405    }
406 
407    if (!ir->write_mask)
408       return;
409 
410    ir_dereference_variable *deref = ir->lhs->as_dereference_variable();
411    ir_constant *constant = ir->rhs->as_constant();
412 
413    if (!deref || !constant)
414       return;
415 
416    /* Only do constant propagation on vectors.  Constant matrices,
417     * arrays, or structures would require more work elsewhere.
418     */
419    if (!deref->var->type->is_vector() && !deref->var->type->is_scalar())
420       return;
421 
422    entry = new(this->mem_ctx) acp_entry(deref->var, ir->write_mask, constant);
423    this->acp->push_tail(entry);
424 }
425 
426 /**
427  * Does a constant propagation pass on the code present in the instruction stream.
428  */
429 bool
do_constant_propagation(exec_list * instructions)430 do_constant_propagation(exec_list *instructions)
431 {
432    ir_constant_propagation_visitor v;
433 
434    visit_list_elements(&v, instructions);
435 
436    return v.progress;
437 }
438