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
41namespace {
42
43class acp_entry : public exec_node
44{
45public:
46   acp_entry(ir_variable *lhs, ir_variable *rhs)
47   {
48      assert(lhs);
49      assert(rhs);
50      this->lhs = lhs;
51      this->rhs = rhs;
52   }
53
54   ir_variable *lhs;
55   ir_variable *rhs;
56};
57
58
59class kill_entry : public exec_node
60{
61public:
62   kill_entry(ir_variable *var)
63   {
64      assert(var);
65      this->var = var;
66   }
67
68   ir_variable *var;
69};
70
71class ir_copy_propagation_visitor : public ir_hierarchical_visitor {
72public:
73   ir_copy_propagation_visitor()
74   {
75      progress = false;
76      mem_ctx = ralloc_context(0);
77      this->acp = new(mem_ctx) exec_list;
78      this->kills = new(mem_ctx) exec_list;
79   }
80   ~ir_copy_propagation_visitor()
81   {
82      ralloc_free(mem_ctx);
83   }
84
85   virtual ir_visitor_status visit(class ir_dereference_variable *);
86   virtual ir_visitor_status visit_enter(class ir_loop *);
87   virtual ir_visitor_status visit_enter(class ir_function_signature *);
88   virtual ir_visitor_status visit_enter(class ir_function *);
89   virtual ir_visitor_status visit_leave(class ir_assignment *);
90   virtual ir_visitor_status visit_enter(class ir_call *);
91   virtual ir_visitor_status visit_enter(class ir_if *);
92
93   void add_copy(ir_assignment *ir);
94   void kill(ir_variable *ir);
95   void handle_if_block(exec_list *instructions);
96
97   /** List of acp_entry: The available copies to propagate */
98   exec_list *acp;
99   /**
100    * List of kill_entry: The variables whose values were killed in this
101    * block.
102    */
103   exec_list *kills;
104
105   bool progress;
106
107   bool killed_all;
108
109   void *mem_ctx;
110};
111
112} /* unnamed namespace */
113
114ir_visitor_status
115ir_copy_propagation_visitor::visit_enter(ir_function_signature *ir)
116{
117   /* Treat entry into a function signature as a completely separate
118    * block.  Any instructions at global scope will be shuffled into
119    * main() at link time, so they're irrelevant to us.
120    */
121   exec_list *orig_acp = this->acp;
122   exec_list *orig_kills = this->kills;
123   bool orig_killed_all = this->killed_all;
124
125   this->acp = new(mem_ctx) exec_list;
126   this->kills = new(mem_ctx) exec_list;
127   this->killed_all = false;
128
129   visit_list_elements(this, &ir->body);
130
131   this->kills = orig_kills;
132   this->acp = orig_acp;
133   this->killed_all = orig_killed_all;
134
135   return visit_continue_with_parent;
136}
137
138ir_visitor_status
139ir_copy_propagation_visitor::visit_leave(ir_assignment *ir)
140{
141   kill(ir->lhs->variable_referenced());
142
143   add_copy(ir);
144
145   return visit_continue;
146}
147
148ir_visitor_status
149ir_copy_propagation_visitor::visit_enter(ir_function *ir)
150{
151   (void) ir;
152   return visit_continue;
153}
154
155/**
156 * Replaces dereferences of ACP RHS variables with ACP LHS variables.
157 *
158 * This is where the actual copy propagation occurs.  Note that the
159 * rewriting of ir_dereference means that the ir_dereference instance
160 * must not be shared by multiple IR operations!
161 */
162ir_visitor_status
163ir_copy_propagation_visitor::visit(ir_dereference_variable *ir)
164{
165   if (this->in_assignee)
166      return visit_continue;
167
168   ir_variable *var = ir->var;
169
170   foreach_iter(exec_list_iterator, iter, *this->acp) {
171      acp_entry *entry = (acp_entry *)iter.get();
172
173      if (var == entry->lhs) {
174	 ir->var = entry->rhs;
175	 this->progress = true;
176	 break;
177      }
178   }
179
180   return visit_continue;
181}
182
183
184ir_visitor_status
185ir_copy_propagation_visitor::visit_enter(ir_call *ir)
186{
187   /* Do copy propagation on call parameters, but skip any out params */
188   exec_list_iterator sig_param_iter = ir->callee->parameters.iterator();
189   foreach_iter(exec_list_iterator, iter, ir->actual_parameters) {
190      ir_variable *sig_param = (ir_variable *)sig_param_iter.get();
191      ir_instruction *ir = (ir_instruction *)iter.get();
192      if (sig_param->mode != ir_var_out && sig_param->mode != ir_var_inout) {
193         ir->accept(this);
194      }
195      sig_param_iter.next();
196   }
197
198   /* Since we're unlinked, we don't (necessarily) know the side effects of
199    * this call.  So kill all copies.
200    */
201   acp->make_empty();
202   this->killed_all = true;
203
204   return visit_continue_with_parent;
205}
206
207void
208ir_copy_propagation_visitor::handle_if_block(exec_list *instructions)
209{
210   exec_list *orig_acp = this->acp;
211   exec_list *orig_kills = this->kills;
212   bool orig_killed_all = this->killed_all;
213
214   this->acp = new(mem_ctx) exec_list;
215   this->kills = new(mem_ctx) exec_list;
216   this->killed_all = false;
217
218   /* Populate the initial acp with a copy of the original */
219   foreach_iter(exec_list_iterator, iter, *orig_acp) {
220      acp_entry *a = (acp_entry *)iter.get();
221      this->acp->push_tail(new(this->mem_ctx) acp_entry(a->lhs, a->rhs));
222   }
223
224   visit_list_elements(this, instructions);
225
226   if (this->killed_all) {
227      orig_acp->make_empty();
228   }
229
230   exec_list *new_kills = this->kills;
231   this->kills = orig_kills;
232   this->acp = orig_acp;
233   this->killed_all = this->killed_all || orig_killed_all;
234
235   foreach_iter(exec_list_iterator, iter, *new_kills) {
236      kill_entry *k = (kill_entry *)iter.get();
237      kill(k->var);
238   }
239}
240
241ir_visitor_status
242ir_copy_propagation_visitor::visit_enter(ir_if *ir)
243{
244   ir->condition->accept(this);
245
246   handle_if_block(&ir->then_instructions);
247   handle_if_block(&ir->else_instructions);
248
249   /* handle_if_block() already descended into the children. */
250   return visit_continue_with_parent;
251}
252
253ir_visitor_status
254ir_copy_propagation_visitor::visit_enter(ir_loop *ir)
255{
256   exec_list *orig_acp = this->acp;
257   exec_list *orig_kills = this->kills;
258   bool orig_killed_all = this->killed_all;
259
260   /* FINISHME: For now, the initial acp for loops is totally empty.
261    * We could go through once, then go through again with the acp
262    * cloned minus the killed entries after the first run through.
263    */
264   this->acp = new(mem_ctx) exec_list;
265   this->kills = new(mem_ctx) exec_list;
266   this->killed_all = false;
267
268   visit_list_elements(this, &ir->body_instructions);
269
270   if (this->killed_all) {
271      orig_acp->make_empty();
272   }
273
274   exec_list *new_kills = this->kills;
275   this->kills = orig_kills;
276   this->acp = orig_acp;
277   this->killed_all = this->killed_all || orig_killed_all;
278
279   foreach_iter(exec_list_iterator, iter, *new_kills) {
280      kill_entry *k = (kill_entry *)iter.get();
281      kill(k->var);
282   }
283
284   /* already descended into the children. */
285   return visit_continue_with_parent;
286}
287
288void
289ir_copy_propagation_visitor::kill(ir_variable *var)
290{
291   assert(var != NULL);
292
293   /* Remove any entries currently in the ACP for this kill. */
294   foreach_iter(exec_list_iterator, iter, *acp) {
295      acp_entry *entry = (acp_entry *)iter.get();
296
297      if (entry->lhs == var || entry->rhs == var) {
298	 entry->remove();
299      }
300   }
301
302   /* Add the LHS variable to the list of killed variables in this block.
303    */
304   this->kills->push_tail(new(this->mem_ctx) kill_entry(var));
305}
306
307/**
308 * Adds an entry to the available copy list if it's a plain assignment
309 * of a variable to a variable.
310 */
311void
312ir_copy_propagation_visitor::add_copy(ir_assignment *ir)
313{
314   acp_entry *entry;
315
316   if (ir->condition)
317      return;
318
319   ir_variable *lhs_var = ir->whole_variable_written();
320   ir_variable *rhs_var = ir->rhs->whole_variable_referenced();
321
322   if ((lhs_var != NULL) && (rhs_var != NULL)) {
323      if (lhs_var == rhs_var) {
324	 /* This is a dumb assignment, but we've conveniently noticed
325	  * it here.  Removing it now would mess up the loop iteration
326	  * calling us.  Just flag it to not execute, and someone else
327	  * will clean up the mess.
328	  */
329	 ir->condition = new(ralloc_parent(ir)) ir_constant(false);
330	 this->progress = true;
331      } else {
332	 entry = new(this->mem_ctx) acp_entry(lhs_var, rhs_var);
333	 this->acp->push_tail(entry);
334      }
335   }
336}
337
338/**
339 * Does a copy propagation pass on the code present in the instruction stream.
340 */
341bool
342do_copy_propagation(exec_list *instructions)
343{
344   ir_copy_propagation_visitor v;
345
346   visit_list_elements(&v, instructions);
347
348   return v.progress;
349}
350