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simplify_expr_array.cpp
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1/*******************************************************************\
2
3Module:
4
5Author: Daniel Kroening, kroening@kroening.com
6
7\*******************************************************************/
8
10
11#include "arith_tools.h"
12#include "byte_operators.h"
13#include "pointer_offset_size.h"
14#include "replace_expr.h"
15#include "std_expr.h"
16#include "string_constant.h"
17
20{
21 bool no_change = true;
22
23 // copy
24 auto new_expr = expr;
25
26 // references
27 auto &index = new_expr.index();
28 auto &array = new_expr.array();
29
30 // extra arithmetic optimizations
31
32 if(index.id() == ID_div)
33 {
34 const auto &index_div_expr = to_div_expr(index);
35
36 if(
37 index_div_expr.dividend().id() == ID_mult &&
38 index_div_expr.dividend().operands().size() == 2 &&
39 to_mult_expr(index_div_expr.dividend()).op1() == index_div_expr.divisor())
40 {
41 // this rewrites (a*b)/b to a
42 index = to_mult_expr(index_div_expr.dividend()).op0();
43 no_change = false;
44 }
45 else if(
46 index_div_expr.dividend().id() == ID_mult &&
47 index_div_expr.dividend().operands().size() == 2 &&
48 to_mult_expr(index_div_expr.dividend()).op0() == index_div_expr.divisor())
49 {
50 // this rewrites (a*b)/a to b
51 index = to_mult_expr(index_div_expr.dividend()).op1();
52 no_change = false;
53 }
54 }
55
56 if(array.id() == ID_array_comprehension)
57 {
58 // simplify (lambda i: e)(x) to e[i/x]
59
60 const auto &comprehension = to_array_comprehension_expr(array);
61
62 if(index.type() == comprehension.arg().type())
63 {
64 exprt tmp = comprehension.body();
65 replace_expr(comprehension.arg(), index, tmp);
66 return changed(simplify_rec(tmp));
67 }
68 }
69 else if(array.id()==ID_with)
70 {
71 // we have (a WITH [i:=e])[j]
72
73 if(array.operands().size() != 3)
74 return unchanged(expr);
75
76 const auto &with_expr = to_with_expr(array);
77
78 if(with_expr.where() == index)
79 {
80 // simplify (e with [i:=v])[i] to v
81 return with_expr.new_value();
82 }
83 else
84 {
85 // Turn (a with i:=x)[j] into (i==j)?x:a[j].
86 // watch out that the type of i and j might be different.
87 const exprt rhs_casted =
88 typecast_exprt::conditional_cast(with_expr.where(), index.type());
89
90 exprt equality_expr = simplify_inequality(equal_exprt(index, rhs_casted));
91
92 exprt new_index_expr = simplify_index(
93 index_exprt(with_expr.old(), index, new_expr.type())); // recursive call
94
95 if(equality_expr.is_true())
96 {
97 return with_expr.new_value();
98 }
99 else if(equality_expr.is_false())
100 {
101 return new_index_expr;
102 }
103
104 if_exprt if_expr(equality_expr, with_expr.new_value(), new_index_expr);
105 return changed(simplify_if(if_expr));
106 }
107 }
108 else if(
109 array.id() == ID_constant || array.id() == ID_array ||
110 array.id() == ID_vector)
111 {
112 const auto i = numeric_cast<mp_integer>(index);
113
114 if(!i.has_value())
115 {
116 }
117 else if(*i < 0 || *i >= array.operands().size())
118 {
119 // out of bounds
120 }
121 else
122 {
123 // ok
124 return array.operands()[numeric_cast_v<std::size_t>(*i)];
125 }
126 }
127 else if(array.id()==ID_string_constant)
128 {
129 const auto i = numeric_cast<mp_integer>(index);
130
131 const std::string &value = id2string(to_string_constant(array).get_value());
132
133 if(!i.has_value())
134 {
135 }
136 else if(*i < 0 || *i > value.size())
137 {
138 // out of bounds
139 }
140 else
141 {
142 // terminating zero?
143 const char v =
144 (*i == value.size()) ? 0 : value[numeric_cast_v<std::size_t>(*i)];
145 return from_integer(v, new_expr.type());
146 }
147 }
148 else if(array.id()==ID_array_of)
149 {
150 return to_array_of_expr(array).what();
151 }
152 else if(array.id() == ID_array_list)
153 {
154 // These are index/value pairs, alternating.
155 for(size_t i=0; i<array.operands().size()/2; i++)
156 {
157 exprt tmp_index = typecast_exprt(array.operands()[i * 2], index.type());
158 simplify(tmp_index);
159 if(tmp_index==index)
160 {
161 return array.operands()[i * 2 + 1];
162 }
163 }
164 }
165 else if(array.id()==ID_byte_extract_little_endian ||
166 array.id()==ID_byte_extract_big_endian)
167 {
168 const auto &byte_extract_expr = to_byte_extract_expr(array);
169
170 if(array.type().id() == ID_array || array.type().id() == ID_vector)
171 {
172 optionalt<typet> subtype;
173 if(array.type().id() == ID_array)
174 subtype = to_array_type(array.type()).element_type();
175 else
176 subtype = to_vector_type(array.type()).element_type();
177
178 // This rewrites byte_extract(s, o, array_type)[i]
179 // to byte_extract(s, o+offset, sub_type)
180
181 auto sub_size = pointer_offset_size(*subtype, ns);
182 if(!sub_size.has_value())
183 return unchanged(expr);
184
185 // add offset to index
187 from_integer(*sub_size, byte_extract_expr.offset().type()), index});
188 exprt final_offset =
189 simplify_plus(plus_exprt(byte_extract_expr.offset(), offset));
190
191 auto result_expr = byte_extract_expr;
192 result_expr.type() = expr.type();
193 result_expr.offset() = final_offset;
194
195 return changed(simplify_byte_extract(result_expr));
196 }
197 }
198 else if(array.id()==ID_if)
199 {
200 const if_exprt &if_expr=to_if_expr(array);
201 exprt cond=if_expr.cond();
202
203 index_exprt idx_false=to_index_expr(expr);
204 idx_false.array()=if_expr.false_case();
205
206 new_expr.array() = if_expr.true_case();
207
208 exprt result = if_exprt(cond, new_expr, idx_false, expr.type());
209 return changed(simplify_rec(result));
210 }
211
212 if(no_change)
213 return unchanged(expr);
214 else
215 return std::move(new_expr);
216}
constant_exprt from_integer(const mp_integer &int_value, const typet &type)
Expression classes for byte-level operators.
const byte_extract_exprt & to_byte_extract_expr(const exprt &expr)
exprt & what()
Definition std_expr.h:1428
const typet & element_type() const
The type of the elements of the array.
Definition std_types.h:777
Equality.
Definition std_expr.h:1225
Base class for all expressions.
Definition expr.h:54
bool is_true() const
Return whether the expression is a constant representing true.
Definition expr.cpp:33
bool is_false() const
Return whether the expression is a constant representing false.
Definition expr.cpp:42
typet & type()
Return the type of the expression.
Definition expr.h:82
The trinary if-then-else operator.
Definition std_expr.h:2226
exprt & cond()
Definition std_expr.h:2243
exprt & false_case()
Definition std_expr.h:2263
exprt & true_case()
Definition std_expr.h:2253
Array index operator.
Definition std_expr.h:1328
exprt & index()
Definition std_expr.h:1363
exprt & array()
Definition std_expr.h:1353
Binary multiplication Associativity is not specified.
Definition std_expr.h:1019
exprt & op1()
Definition std_expr.h:850
exprt & op0()
Definition std_expr.h:844
The plus expression Associativity is not specified.
Definition std_expr.h:914
const namespacet & ns
resultt simplify_byte_extract(const byte_extract_exprt &)
static resultt changed(resultt<> result)
resultt simplify_if(const if_exprt &)
resultt simplify_rec(const exprt &)
resultt simplify_mult(const mult_exprt &)
resultt simplify_inequality(const binary_relation_exprt &)
simplifies inequalities !=, <=, <, >=, >, and also ==
resultt simplify_index(const index_exprt &)
static resultt unchanged(exprt expr)
resultt simplify_plus(const plus_exprt &)
virtual bool simplify(exprt &expr)
Semantic type conversion.
Definition std_expr.h:1920
static exprt conditional_cast(const exprt &expr, const typet &type)
Definition std_expr.h:1928
const typet & element_type() const
The type of the elements of the vector.
Definition std_types.h:1006
const std::string & id2string(const irep_idt &d)
Definition irep.h:47
nonstd::optional< T > optionalt
Definition optional.h:35
optionalt< mp_integer > pointer_offset_size(const typet &type, const namespacet &ns)
Compute the size of a type in bytes, rounding up to full bytes.
Pointer Logic.
bool replace_expr(const exprt &what, const exprt &by, exprt &dest)
API to expression classes.
const array_of_exprt & to_array_of_expr(const exprt &expr)
Cast an exprt to an array_of_exprt.
Definition std_expr.h:1456
const index_exprt & to_index_expr(const exprt &expr)
Cast an exprt to an index_exprt.
Definition std_expr.h:1391
const mult_exprt & to_mult_expr(const exprt &expr)
Cast an exprt to a mult_exprt.
Definition std_expr.h:1044
const array_comprehension_exprt & to_array_comprehension_expr(const exprt &expr)
Cast an exprt to a array_comprehension_exprt.
Definition std_expr.h:3249
const div_exprt & to_div_expr(const exprt &expr)
Cast an exprt to a div_exprt.
Definition std_expr.h:1113
const if_exprt & to_if_expr(const exprt &expr)
Cast an exprt to an if_exprt.
Definition std_expr.h:2291
const with_exprt & to_with_expr(const exprt &expr)
Cast an exprt to a with_exprt.
Definition std_expr.h:2374
const vector_typet & to_vector_type(const typet &type)
Cast a typet to a vector_typet.
Definition std_types.h:1040
const array_typet & to_array_type(const typet &type)
Cast a typet to an array_typet.
Definition std_types.h:832
const string_constantt & to_string_constant(const exprt &expr)