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Merge pull request #8400 from tautschnig/bugfixes/smt2-8399
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SMT2 back-end: fix inconsistent array flattening
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@tautschnig
tautschnig authored Sep 2, 2024
2 parents c193c27 + af46479 commit 59674e3
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Showing 3 changed files with 95 additions and 55 deletions.
35 changes: 35 additions & 0 deletions src/solvers/flattening/arrays.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -12,6 +12,7 @@ Author: Daniel Kroening, [email protected]
#include <util/json.h>
#include <util/message.h>
#include <util/replace_expr.h>
#include <util/replace_symbol.h>
#include <util/std_expr.h>

#include <solvers/prop/literal_expr.h>
Expand Down Expand Up @@ -237,6 +238,11 @@ void arrayst::collect_arrays(const exprt &a)
else if(a.id() == ID_array_comprehension)
{
}
else if(auto let_expr = expr_try_dynamic_cast<let_exprt>(a))
{
arrays.make_union(a, let_expr->where());
collect_arrays(let_expr->where());
}
else
{
DATA_INVARIANT(
Expand Down Expand Up @@ -528,6 +534,33 @@ void arrayst::add_array_constraints(
else if(expr.id()==ID_index)
{
}
else if(auto let_expr = expr_try_dynamic_cast<let_exprt>(expr))
{
// we got x=let(a=e, A)
// add x[i]=A[a/e][i]

exprt where = let_expr->where();
replace_symbolt replace_symbol;
for(const auto &binding :
make_range(let_expr->variables()).zip(let_expr->values()))
{
replace_symbol.insert(binding.first, binding.second);
}
replace_symbol(where);

for(const auto &index : index_set)
{
index_exprt index_expr{expr, index};
index_exprt where_indexed{where, index};

// add constraint
lazy_constraintt lazy{
lazy_typet::ARRAY_LET, equal_exprt{index_expr, where_indexed}};

add_array_constraint(lazy, false); // added immediately
array_constraint_count[constraint_typet::ARRAY_LET]++;
}
}
else
{
DATA_INVARIANT(
Expand Down Expand Up @@ -875,6 +908,8 @@ std::string arrayst::enum_to_string(constraint_typet type)
return "arrayComprehension";
case constraint_typet::ARRAY_EQUALITY:
return "arrayEquality";
case constraint_typet::ARRAY_LET:
return "arrayLet";
default:
UNREACHABLE;
}
Expand Down
6 changes: 4 additions & 2 deletions src/solvers/flattening/arrays.h
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Original file line number Diff line number Diff line change
Expand Up @@ -93,7 +93,8 @@ class arrayst:public equalityt
ARRAY_OF,
ARRAY_TYPECAST,
ARRAY_CONSTANT,
ARRAY_COMPREHENSION
ARRAY_COMPREHENSION,
ARRAY_LET
};

struct lazy_constraintt
Expand Down Expand Up @@ -124,7 +125,8 @@ class arrayst:public equalityt
ARRAY_TYPECAST,
ARRAY_CONSTANT,
ARRAY_COMPREHENSION,
ARRAY_EQUALITY
ARRAY_EQUALITY,
ARRAY_LET
};

typedef std::map<constraint_typet, size_t> array_constraint_countt;
Expand Down
109 changes: 56 additions & 53 deletions src/solvers/smt2/smt2_conv.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -4445,15 +4445,22 @@ void smt2_convt::convert_member(const member_exprt &expr)
CHECK_RETURN_WITH_DIAGNOSTICS(
width != 0, "failed to get union member width");

unflatten(wheret::BEGIN, expr.type());
if(use_datatypes)
{
unflatten(wheret::BEGIN, expr.type());

out << "((_ extract "
<< (width-1)
<< " 0) ";
convert_expr(struct_op);
out << ")";
out << "((_ extract " << (width - 1) << " 0) ";
convert_expr(struct_op);
out << ")";

unflatten(wheret::END, expr.type());
unflatten(wheret::END, expr.type());
}
else
{
out << "((_ extract " << (width - 1) << " 0) ";
convert_expr(struct_op);
out << ")";
}
}
else
UNEXPECTEDCASE(
Expand Down Expand Up @@ -4565,57 +4572,50 @@ void smt2_convt::unflatten(
}
else if(type.id() == ID_array)
{
if(use_datatypes)
PRECONDITION(use_as_const);

if(where == wheret::BEGIN)
out << "(let ((?ufop" << nesting << " ";
else
{
PRECONDITION(use_as_const);
out << ")) ";

if(where == wheret::BEGIN)
out << "(let ((?ufop" << nesting << " ";
else
{
out << ")) ";
const array_typet &array_type = to_array_type(type);

const array_typet &array_type = to_array_type(type);
std::size_t subtype_width = boolbv_width(array_type.element_type());

std::size_t subtype_width = boolbv_width(array_type.element_type());
DATA_INVARIANT(
array_type.size().is_constant(),
"cannot unflatten arrays of non-constant size");
mp_integer size =
numeric_cast_v<mp_integer>(to_constant_expr(array_type.size()));

DATA_INVARIANT(
array_type.size().is_constant(),
"cannot unflatten arrays of non-constant size");
mp_integer size =
numeric_cast_v<mp_integer>(to_constant_expr(array_type.size()));
for(mp_integer i = 1; i < size; ++i)
out << "(store ";

for(mp_integer i = 1; i < size; ++i)
out << "(store ";
out << "((as const ";
convert_type(array_type);
out << ") ";
// use element at index 0 as default value
unflatten(wheret::BEGIN, array_type.element_type(), nesting + 1);
out << "((_ extract " << subtype_width - 1 << " "
<< "0) ?ufop" << nesting << ")";
unflatten(wheret::END, array_type.element_type(), nesting + 1);
out << ") ";

out << "((as const ";
convert_type(array_type);
out << ") ";
// use element at index 0 as default value
std::size_t offset = subtype_width;
for(mp_integer i = 1; i < size; ++i, offset += subtype_width)
{
convert_expr(from_integer(i, array_type.index_type()));
out << ' ';
unflatten(wheret::BEGIN, array_type.element_type(), nesting + 1);
out << "((_ extract " << subtype_width - 1 << " "
<< "0) ?ufop" << nesting << ")";
out << "((_ extract " << offset + subtype_width - 1 << " " << offset
<< ") ?ufop" << nesting << ")";
unflatten(wheret::END, array_type.element_type(), nesting + 1);
out << ") ";

std::size_t offset = subtype_width;
for(mp_integer i = 1; i < size; ++i, offset += subtype_width)
{
convert_expr(from_integer(i, array_type.index_type()));
out << ' ';
unflatten(wheret::BEGIN, array_type.element_type(), nesting + 1);
out << "((_ extract " << offset + subtype_width - 1 << " " << offset
<< ") ?ufop" << nesting << ")";
unflatten(wheret::END, array_type.element_type(), nesting + 1);
out << ")"; // store
}

out << ")"; // let
out << ")"; // store
}
}
else
{
// nop, already a bv

out << ")"; // let
}
}
else if(type.id() == ID_struct || type.id() == ID_struct_tag)
Expand Down Expand Up @@ -4767,19 +4767,22 @@ void smt2_convt::set_to(const exprt &expr, bool value)
{
out << "(define-fun " << smt2_identifier;
out << " () ";
convert_type(equal_expr.lhs().type());
out << ' ';
if(
equal_expr.lhs().type().id() != ID_array ||
use_array_theory(prepared_rhs))
{
convert_type(equal_expr.lhs().type());
convert_expr(prepared_rhs);
}
else
{
std::size_t width = boolbv_width(equal_expr.lhs().type());
out << "(_ BitVec " << width << ")";
unflatten(wheret::BEGIN, equal_expr.lhs().type());

convert_expr(prepared_rhs);

unflatten(wheret::END, equal_expr.lhs().type());
}
out << ' ';
convert_expr(prepared_rhs);
out << ')' << '\n';
}

Expand Down

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