1/*
2 * Copyright © 2010 Intel Corporation
3 *
4 * Permission is hereby granted, free of charge, to any person obtaining a
5 * copy 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, copy, 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 copyright 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 COPYRIGHT 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_copy_propagation.cpp
26 *
27 * Moves usage of recently-copied variables to the previous copy of
28 * the variable.
29 *
30 * This should reduce the number of MOV instructions in the generated
31 * programs unless copy propagation is also done on the LIR, and may
32 * help anyway by triggering other optimizations that live in the HIR.
33 */
34
35#include "ir.h"
36#include "ir_visitor.h"
37#include "ir_basic_block.h"
38#include "ir_optimization.h"
39#include "glsl_types.h"
40
41class acp_entry : public exec_node
42{
43public:
44   acp_entry(ir_variable *lhs, ir_variable *rhs)
45   {
46      assert(lhs);
47      assert(rhs);
48      this->lhs = lhs;
49      this->rhs = rhs;
50   }
51
52   ir_variable *lhs;
53   ir_variable *rhs;
54};
55
56
57class kill_entry : public exec_node
58{
59public:
60   kill_entry(ir_variable *var)
61   {
62      assert(var);
63      this->var = var;
64   }
65
66   ir_variable *var;
67};
68
69class ir_copy_propagation_visitor : public ir_hierarchical_visitor {
70public:
71   ir_copy_propagation_visitor()
72   {
73      progress = false;
74      mem_ctx = hieralloc_new(0);
75      this->acp = new(mem_ctx) exec_list;
76      this->kills = new(mem_ctx) exec_list;
77   }
78   ~ir_copy_propagation_visitor()
79   {
80      hieralloc_free(mem_ctx);
81   }
82
83   virtual ir_visitor_status visit(class ir_dereference_variable *);
84   virtual ir_visitor_status visit_enter(class ir_loop *);
85   virtual ir_visitor_status visit_enter(class ir_function_signature *);
86   virtual ir_visitor_status visit_enter(class ir_function *);
87   virtual ir_visitor_status visit_leave(class ir_assignment *);
88   virtual ir_visitor_status visit_enter(class ir_call *);
89   virtual ir_visitor_status visit_enter(class ir_if *);
90
91   void add_copy(ir_assignment *ir);
92   void kill(ir_variable *ir);
93   void handle_if_block(exec_list *instructions);
94
95   /** List of acp_entry: The available copies to propagate */
96   exec_list *acp;
97   /**
98    * List of kill_entry: The variables whose values were killed in this
99    * block.
100    */
101   exec_list *kills;
102
103   bool progress;
104
105   bool killed_all;
106
107   void *mem_ctx;
108};
109
110ir_visitor_status
111ir_copy_propagation_visitor::visit_enter(ir_function_signature *ir)
112{
113   /* Treat entry into a function signature as a completely separate
114    * block.  Any instructions at global scope will be shuffled into
115    * main() at link time, so they're irrelevant to us.
116    */
117   exec_list *orig_acp = this->acp;
118   exec_list *orig_kills = this->kills;
119   bool orig_killed_all = this->killed_all;
120
121   this->acp = new(mem_ctx) exec_list;
122   this->kills = new(mem_ctx) exec_list;
123   this->killed_all = false;
124
125   visit_list_elements(this, &ir->body);
126
127   this->kills = orig_kills;
128   this->acp = orig_acp;
129   this->killed_all = orig_killed_all;
130
131   return visit_continue_with_parent;
132}
133
134ir_visitor_status
135ir_copy_propagation_visitor::visit_leave(ir_assignment *ir)
136{
137   kill(ir->lhs->variable_referenced());
138
139   add_copy(ir);
140
141   return visit_continue;
142}
143
144ir_visitor_status
145ir_copy_propagation_visitor::visit_enter(ir_function *ir)
146{
147   (void) ir;
148   return visit_continue;
149}
150
151/**
152 * Replaces dereferences of ACP RHS variables with ACP LHS variables.
153 *
154 * This is where the actual copy propagation occurs.  Note that the
155 * rewriting of ir_dereference means that the ir_dereference instance
156 * must not be shared by multiple IR operations!
157 */
158ir_visitor_status
159ir_copy_propagation_visitor::visit(ir_dereference_variable *ir)
160{
161   if (this->in_assignee)
162      return visit_continue;
163
164   ir_variable *var = ir->var;
165
166   foreach_iter(exec_list_iterator, iter, *this->acp) {
167      acp_entry *entry = (acp_entry *)iter.get();
168
169      if (var == entry->lhs) {
170	 ir->var = entry->rhs;
171	 this->progress = true;
172	 break;
173      }
174   }
175
176   return visit_continue;
177}
178
179
180ir_visitor_status
181ir_copy_propagation_visitor::visit_enter(ir_call *ir)
182{
183   /* Do copy propagation on call parameters, but skip any out params */
184   exec_list_iterator sig_param_iter = ir->get_callee()->parameters.iterator();
185   foreach_iter(exec_list_iterator, iter, ir->actual_parameters) {
186      ir_variable *sig_param = (ir_variable *)sig_param_iter.get();
187      ir_instruction *ir = (ir_instruction *)iter.get();
188      if (sig_param->mode != ir_var_out && sig_param->mode != ir_var_inout) {
189         ir->accept(this);
190      }
191      sig_param_iter.next();
192   }
193
194   /* Since we're unlinked, we don't (necssarily) know the side effects of
195    * this call.  So kill all copies.
196    */
197   acp->make_empty();
198   this->killed_all = true;
199
200   return visit_continue_with_parent;
201}
202
203void
204ir_copy_propagation_visitor::handle_if_block(exec_list *instructions)
205{
206   exec_list *orig_acp = this->acp;
207   exec_list *orig_kills = this->kills;
208   bool orig_killed_all = this->killed_all;
209
210   this->acp = new(mem_ctx) exec_list;
211   this->kills = new(mem_ctx) exec_list;
212   this->killed_all = false;
213
214   /* Populate the initial acp with a copy of the original */
215   foreach_iter(exec_list_iterator, iter, *orig_acp) {
216      acp_entry *a = (acp_entry *)iter.get();
217      this->acp->push_tail(new(this->mem_ctx) acp_entry(a->lhs, a->rhs));
218   }
219
220   visit_list_elements(this, instructions);
221
222   if (this->killed_all) {
223      orig_acp->make_empty();
224   }
225
226   exec_list *new_kills = this->kills;
227   this->kills = orig_kills;
228   this->acp = orig_acp;
229   this->killed_all = this->killed_all || orig_killed_all;
230
231   foreach_iter(exec_list_iterator, iter, *new_kills) {
232      kill_entry *k = (kill_entry *)iter.get();
233      kill(k->var);
234   }
235}
236
237ir_visitor_status
238ir_copy_propagation_visitor::visit_enter(ir_if *ir)
239{
240   ir->condition->accept(this);
241
242   handle_if_block(&ir->then_instructions);
243   handle_if_block(&ir->else_instructions);
244
245   /* handle_if_block() already descended into the children. */
246   return visit_continue_with_parent;
247}
248
249ir_visitor_status
250ir_copy_propagation_visitor::visit_enter(ir_loop *ir)
251{
252   exec_list *orig_acp = this->acp;
253   exec_list *orig_kills = this->kills;
254   bool orig_killed_all = this->killed_all;
255
256   /* FINISHME: For now, the initial acp for loops is totally empty.
257    * We could go through once, then go through again with the acp
258    * cloned minus the killed entries after the first run through.
259    */
260   this->acp = new(mem_ctx) exec_list;
261   this->kills = new(mem_ctx) exec_list;
262   this->killed_all = false;
263
264   visit_list_elements(this, &ir->body_instructions);
265
266   if (this->killed_all) {
267      orig_acp->make_empty();
268   }
269
270   exec_list *new_kills = this->kills;
271   this->kills = orig_kills;
272   this->acp = orig_acp;
273   this->killed_all = this->killed_all || orig_killed_all;
274
275   foreach_iter(exec_list_iterator, iter, *new_kills) {
276      kill_entry *k = (kill_entry *)iter.get();
277      kill(k->var);
278   }
279
280   /* already descended into the children. */
281   return visit_continue_with_parent;
282}
283
284void
285ir_copy_propagation_visitor::kill(ir_variable *var)
286{
287   assert(var != NULL);
288
289   /* Remove any entries currently in the ACP for this kill. */
290   foreach_iter(exec_list_iterator, iter, *acp) {
291      acp_entry *entry = (acp_entry *)iter.get();
292
293      if (entry->lhs == var || entry->rhs == var) {
294	 entry->remove();
295      }
296   }
297
298   /* Add the LHS variable to the list of killed variables in this block.
299    */
300   this->kills->push_tail(new(this->mem_ctx) kill_entry(var));
301}
302
303/**
304 * Adds an entry to the available copy list if it's a plain assignment
305 * of a variable to a variable.
306 */
307void
308ir_copy_propagation_visitor::add_copy(ir_assignment *ir)
309{
310   acp_entry *entry;
311
312   if (ir->condition) {
313      ir_constant *condition = ir->condition->as_constant();
314      if (!condition || !condition->value.b[0])
315	 return;
316   }
317
318   ir_variable *lhs_var = ir->whole_variable_written();
319   ir_variable *rhs_var = ir->rhs->whole_variable_referenced();
320
321   if ((lhs_var != NULL) && (rhs_var != NULL)) {
322      if (lhs_var == rhs_var) {
323	 /* This is a dumb assignment, but we've conveniently noticed
324	  * it here.  Removing it now would mess up the loop iteration
325	  * calling us.  Just flag it to not execute, and someone else
326	  * will clean up the mess.
327	  */
328	 ir->condition = new(hieralloc_parent(ir)) ir_constant(false);
329	 this->progress = true;
330      } else {
331	 entry = new(this->mem_ctx) acp_entry(lhs_var, rhs_var);
332	 this->acp->push_tail(entry);
333      }
334   }
335}
336
337/**
338 * Does a copy propagation pass on the code present in the instruction stream.
339 */
340bool
341do_copy_propagation(exec_list *instructions)
342{
343   ir_copy_propagation_visitor v;
344
345   visit_list_elements(&v, instructions);
346
347   return v.progress;
348}
349