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_constant_folding.cpp
26 * Replace constant-valued expressions with references to constant values.
27 */
28
29#include "ir.h"
30#include "ir_visitor.h"
31#include "ir_rvalue_visitor.h"
32#include "ir_optimization.h"
33#include "compiler/glsl_types.h"
34
35namespace {
36
37/**
38 * Visitor class for replacing expressions with ir_constant values.
39 */
40
41class ir_constant_folding_visitor : public ir_rvalue_visitor {
42public:
43   ir_constant_folding_visitor()
44   {
45      this->progress = false;
46   }
47
48   virtual ~ir_constant_folding_visitor()
49   {
50      /* empty */
51   }
52
53   virtual ir_visitor_status visit_enter(ir_discard *ir);
54   virtual ir_visitor_status visit_enter(ir_assignment *ir);
55   virtual ir_visitor_status visit_enter(ir_call *ir);
56
57   virtual void handle_rvalue(ir_rvalue **rvalue);
58
59   bool progress;
60};
61
62} /* unnamed namespace */
63
64bool
65ir_constant_fold(ir_rvalue **rvalue)
66{
67   if (*rvalue == NULL || (*rvalue)->ir_type == ir_type_constant)
68      return false;
69
70   /* Note that we do rvalue visitoring on leaving.  So if an
71    * expression has a non-constant operand, no need to go looking
72    * down it to find if it's constant.  This cuts the time of this
73    * pass down drastically.
74    */
75   ir_expression *expr = (*rvalue)->as_expression();
76   if (expr) {
77      for (unsigned int i = 0; i < expr->num_operands; i++) {
78	 if (!expr->operands[i]->as_constant())
79	    return false;
80      }
81   }
82
83   /* Ditto for swizzles. */
84   ir_swizzle *swiz = (*rvalue)->as_swizzle();
85   if (swiz && !swiz->val->as_constant())
86      return false;
87
88   /* Ditto for array dereferences */
89   ir_dereference_array *array_ref = (*rvalue)->as_dereference_array();
90   if (array_ref && (!array_ref->array->as_constant() ||
91                     !array_ref->array_index->as_constant()))
92      return false;
93
94   /* No constant folding can be performed on variable dereferences.  We need
95    * to explicitly avoid them, as calling constant_expression_value() on a
96    * variable dereference will return a clone of var->constant_value.  This
97    * would make us propagate the value into the tree, which isn't our job.
98    */
99   ir_dereference_variable *var_ref = (*rvalue)->as_dereference_variable();
100   if (var_ref)
101      return false;
102
103   ir_constant *constant =
104      (*rvalue)->constant_expression_value(ralloc_parent(*rvalue));
105   if (constant) {
106      *rvalue = constant;
107      return true;
108   }
109   return false;
110}
111
112void
113ir_constant_folding_visitor::handle_rvalue(ir_rvalue **rvalue)
114{
115   if (ir_constant_fold(rvalue))
116      this->progress = true;
117}
118
119ir_visitor_status
120ir_constant_folding_visitor::visit_enter(ir_discard *ir)
121{
122   if (ir->condition) {
123      ir->condition->accept(this);
124      handle_rvalue(&ir->condition);
125
126      ir_constant *const_val = ir->condition->as_constant();
127      /* If the condition is constant, either remove the condition or
128       * remove the never-executed assignment.
129       */
130      if (const_val) {
131         if (const_val->value.b[0])
132            ir->condition = NULL;
133         else
134            ir->remove();
135         this->progress = true;
136      }
137   }
138
139   return visit_continue_with_parent;
140}
141
142ir_visitor_status
143ir_constant_folding_visitor::visit_enter(ir_assignment *ir)
144{
145   ir->rhs->accept(this);
146   handle_rvalue(&ir->rhs);
147
148   if (ir->condition) {
149      ir->condition->accept(this);
150      handle_rvalue(&ir->condition);
151
152      ir_constant *const_val = ir->condition->as_constant();
153      /* If the condition is constant, either remove the condition or
154       * remove the never-executed assignment.
155       */
156      if (const_val) {
157	 if (const_val->value.b[0])
158	    ir->condition = NULL;
159	 else
160	    ir->remove();
161	 this->progress = true;
162      }
163   }
164
165   /* Don't descend into the LHS because we want it to stay as a
166    * variable dereference.  FINISHME: We probably should to get array
167    * indices though.
168    */
169   return visit_continue_with_parent;
170}
171
172ir_visitor_status
173ir_constant_folding_visitor::visit_enter(ir_call *ir)
174{
175   /* Attempt to constant fold parameters */
176   foreach_two_lists(formal_node, &ir->callee->parameters,
177                     actual_node, &ir->actual_parameters) {
178      ir_rvalue *param_rval = (ir_rvalue *) actual_node;
179      ir_variable *sig_param = (ir_variable *) formal_node;
180
181      if (sig_param->data.mode == ir_var_function_in
182          || sig_param->data.mode == ir_var_const_in) {
183	 ir_rvalue *new_param = param_rval;
184
185	 handle_rvalue(&new_param);
186	 if (new_param != param_rval) {
187	    param_rval->replace_with(new_param);
188	 }
189      }
190   }
191
192   /* Next, see if the call can be replaced with an assignment of a constant */
193   ir_constant *const_val = ir->constant_expression_value(ralloc_parent(ir));
194
195   if (const_val != NULL) {
196      ir_assignment *assignment =
197	 new(ralloc_parent(ir)) ir_assignment(ir->return_deref, const_val);
198      ir->replace_with(assignment);
199   }
200
201   return visit_continue_with_parent;
202}
203
204bool
205do_constant_folding(exec_list *instructions)
206{
207   ir_constant_folding_visitor constant_folding;
208
209   visit_list_elements(&constant_folding, instructions);
210
211   return constant_folding.progress;
212}
213