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merged 2 commits into from
Nov 8, 2023
Merged

Use simplify_exprtt::resultt in pre-order simplification steps #6118

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183bc7e
Use simplify_exprtt::resultt in pre-order simplification steps
tautschnig Jan 8, 2021
5d29491
Simplify selected ID_if operands in preorder traversal
tautschnig May 9, 2023
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235 changes: 151 additions & 84 deletions src/util/simplify_expr.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -820,9 +820,8 @@ simplify_exprt::simplify_typecast(const typecast_exprt &expr)
// rewrite (T)(bool) to bool?1:0
auto one = from_integer(1, expr_type);
auto zero = from_integer(0, expr_type);
exprt new_expr = if_exprt(expr.op(), std::move(one), std::move(zero));
simplify_if_preorder(to_if_expr(new_expr));
return new_expr;
return changed(simplify_if_preorder(
if_exprt{expr.op(), std::move(one), std::move(zero)}));
}

// circular casts through types shorter than `int`
Expand Down Expand Up @@ -1340,33 +1339,33 @@ simplify_exprt::simplify_typecast(const typecast_exprt &expr)
return unchanged(expr);
}

bool simplify_exprt::simplify_typecast_preorder(typecast_exprt &expr)
simplify_exprt::resultt<>
simplify_exprt::simplify_typecast_preorder(const typecast_exprt &expr)
{
const typet &expr_type = as_const(expr).type();
const typet &op_type = as_const(expr).op().type();
const typet &expr_type = expr.type();
const typet &op_type = expr.op().type();

// (T)(a?b:c) --> a?(T)b:(T)c; don't do this for floating-point type casts as
// the type cast itself may be costly
if(
as_const(expr).op().id() == ID_if && expr_type.id() != ID_floatbv &&
expr.op().id() == ID_if && expr_type.id() != ID_floatbv &&
op_type.id() != ID_floatbv)
{
if_exprt if_expr = lift_if(expr, 0);
simplify_if_preorder(if_expr);
expr.swap(if_expr);
return false;
return changed(simplify_if_preorder(if_expr));
}
else
{
auto r_it = simplify_rec(expr.op()); // recursive call
if(r_it.has_changed())
{
expr.op() = r_it.expr;
return false;
auto tmp = expr;
tmp.op() = r_it.expr;
return tmp;
}
else
return true;
}

return unchanged(expr);
}

simplify_exprt::resultt<>
Expand All @@ -1377,23 +1376,6 @@ simplify_exprt::simplify_dereference(const dereference_exprt &expr)
if(pointer.type().id()!=ID_pointer)
return unchanged(expr);

if(pointer.id()==ID_if && pointer.operands().size()==3)
{
const if_exprt &if_expr=to_if_expr(pointer);

auto tmp_op1 = expr;
tmp_op1.op() = if_expr.true_case();
exprt tmp_op1_result = simplify_dereference(tmp_op1);

auto tmp_op2 = expr;
tmp_op2.op() = if_expr.false_case();
exprt tmp_op2_result = simplify_dereference(tmp_op2);

if_exprt tmp{if_expr.cond(), tmp_op1_result, tmp_op2_result};

return changed(simplify_if(tmp));
}

if(pointer.id()==ID_address_of)
{
exprt tmp=to_address_of_expr(pointer).object();
Expand Down Expand Up @@ -1427,6 +1409,30 @@ simplify_exprt::simplify_dereference(const dereference_exprt &expr)
return unchanged(expr);
}

simplify_exprt::resultt<>
simplify_exprt::simplify_dereference_preorder(const dereference_exprt &expr)
{
const exprt &pointer = expr.pointer();

if(pointer.id() == ID_if)
{
if_exprt if_expr = lift_if(expr, 0);
return changed(simplify_if_preorder(if_expr));
}
else
{
auto r_it = simplify_rec(pointer); // recursive call
if(r_it.has_changed())
{
auto tmp = expr;
tmp.pointer() = r_it.expr;
return tmp;
}
}

return unchanged(expr);
}

simplify_exprt::resultt<>
simplify_exprt::simplify_lambda(const lambda_exprt &expr)
{
Expand Down Expand Up @@ -1643,17 +1649,6 @@ simplify_exprt::resultt<> simplify_exprt::simplify_object(const exprt &expr)
simplify_exprt::resultt<>
simplify_exprt::simplify_byte_extract(const byte_extract_exprt &expr)
{
// lift up any ID_if on the object
if(expr.op().id()==ID_if)
{
if_exprt if_expr=lift_if(expr, 0);
if_expr.true_case() =
simplify_byte_extract(to_byte_extract_expr(if_expr.true_case()));
if_expr.false_case() =
simplify_byte_extract(to_byte_extract_expr(if_expr.false_case()));
return changed(simplify_if(if_expr));
}

const auto el_size = pointer_offset_bits(expr.type(), ns);
if(el_size.has_value() && *el_size < 0)
return unchanged(expr);
Expand Down Expand Up @@ -2011,6 +2006,41 @@ simplify_exprt::simplify_byte_extract(const byte_extract_exprt &expr)
return unchanged(expr);
}

simplify_exprt::resultt<>
simplify_exprt::simplify_byte_extract_preorder(const byte_extract_exprt &expr)
{
// lift up any ID_if on the object
if(expr.op().id() == ID_if)
{
if_exprt if_expr = lift_if(expr, 0);
return changed(simplify_if_preorder(if_expr));
}
else
{
optionalt<exprt::operandst> new_operands;

for(std::size_t i = 0; i < expr.operands().size(); ++i)
{
auto r_it = simplify_rec(expr.operands()[i]); // recursive call
if(r_it.has_changed())
{
if(!new_operands.has_value())
new_operands = expr.operands();
(*new_operands)[i] = std::move(r_it.expr);
}
}

if(new_operands.has_value())
{
exprt result = expr;
std::swap(result.operands(), *new_operands);
return result;
}
}

return unchanged(expr);
}

simplify_exprt::resultt<>
simplify_exprt::simplify_byte_update(const byte_update_exprt &expr)
{
Expand Down Expand Up @@ -2721,9 +2751,10 @@ simplify_exprt::simplify_overflow_result(const overflow_result_exprt &expr)
}
}

bool simplify_exprt::simplify_node_preorder(exprt &expr)
simplify_exprt::resultt<>
simplify_exprt::simplify_node_preorder(const exprt &expr)
{
bool result=true;
auto result = unchanged(expr);

// The ifs below could one day be replaced by a switch()

Expand All @@ -2732,40 +2763,75 @@ bool simplify_exprt::simplify_node_preorder(exprt &expr)
// the argument of this expression needs special treatment
}
else if(expr.id()==ID_if)
result=simplify_if_preorder(to_if_expr(expr));
{
result = simplify_if_preorder(to_if_expr(expr));
}
else if(expr.id() == ID_typecast)
{
result = simplify_typecast_preorder(to_typecast_expr(expr));
else
}
else if(
expr.id() == ID_byte_extract_little_endian ||
expr.id() == ID_byte_extract_big_endian)
{
result = simplify_byte_extract_preorder(to_byte_extract_expr(expr));
}
else if(expr.id() == ID_dereference)
{
result = simplify_dereference_preorder(to_dereference_expr(expr));
}
else if(expr.id() == ID_index)
{
if(expr.has_operands())
result = simplify_index_preorder(to_index_expr(expr));
}
else if(expr.id() == ID_member)
{
result = simplify_member_preorder(to_member_expr(expr));
}
else if(
expr.id() == ID_is_dynamic_object || expr.id() == ID_is_invalid_pointer ||
expr.id() == ID_object_size || expr.id() == ID_pointer_object ||
expr.id() == ID_pointer_offset)
{
result = simplify_unary_pointer_predicate_preorder(to_unary_expr(expr));
}
else if(expr.has_operands())
{
optionalt<exprt::operandst> new_operands;

for(std::size_t i = 0; i < expr.operands().size(); ++i)
{
Forall_operands(it, expr)
auto r_it = simplify_rec(expr.operands()[i]); // recursive call
if(r_it.has_changed())
{
auto r_it = simplify_rec(*it); // recursive call
if(r_it.has_changed())
{
*it = r_it.expr;
result=false;
}
if(!new_operands.has_value())
new_operands = expr.operands();
(*new_operands)[i] = std::move(r_it.expr);
}
}

if(new_operands.has_value())
{
std::swap(result.expr.operands(), *new_operands);
result.expr_changed = resultt<>::CHANGED;
}
}

if(as_const(expr).type().id() == ID_array)
if(as_const(result.expr).type().id() == ID_array)
{
const array_typet &array_type = to_array_type(as_const(expr).type());
const array_typet &array_type = to_array_type(as_const(result.expr).type());
resultt<> simp_size = simplify_rec(array_type.size());
if(simp_size.has_changed())
{
to_array_type(expr.type()).size() = simp_size.expr;
result = false;
to_array_type(result.expr.type()).size() = simp_size.expr;
result.expr_changed = resultt<>::CHANGED;
}
}

return result;
}

simplify_exprt::resultt<> simplify_exprt::simplify_node(exprt node)
simplify_exprt::resultt<> simplify_exprt::simplify_node(const exprt &node)
{
if(!node.has_operands())
return unchanged(node); // no change
Expand Down Expand Up @@ -3062,53 +3128,54 @@ simplify_exprt::resultt<> simplify_exprt::simplify_rec(const exprt &expr)
#endif

// We work on a copy to prevent unnecessary destruction of sharing.
exprt tmp=expr;
bool no_change = simplify_node_preorder(tmp);
auto simplify_node_preorder_result = simplify_node_preorder(expr);

auto simplify_node_result = simplify_node(tmp);
auto simplify_node_result = simplify_node(simplify_node_preorder_result.expr);

if(simplify_node_result.has_changed())
if(
!simplify_node_result.has_changed() &&
simplify_node_preorder_result.has_changed())
{
no_change = false;
tmp = simplify_node_result.expr;
simplify_node_result.expr_changed =
simplify_node_preorder_result.expr_changed;
}

#ifdef USE_LOCAL_REPLACE_MAP
#if 1
replace_mapt::const_iterator it=local_replace_map.find(tmp);
exprt tmp = simplify_node_result.expr;
# if 1
replace_mapt::const_iterator it =
local_replace_map.find(simplify_node_result.expr);
if(it!=local_replace_map.end())
simplify_node_result = changed(it->second);
# else
if(
!local_replace_map.empty() &&
!replace_expr(local_replace_map, simplify_node_result.expr))
{
tmp=it->second;
no_change = false;
}
#else
if(!local_replace_map.empty() &&
!replace_expr(local_replace_map, tmp))
{
simplify_rec(tmp);
no_change = false;
simplify_node_result = changed(simplify_rec(simplify_node_result.expr));
}
#endif
# endif
#endif

if(no_change) // no change
if(!simplify_node_result.has_changed())
{
return unchanged(expr);
}
else // change, new expression is 'tmp'
else
{
POSTCONDITION_WITH_DIAGNOSTICS(
(as_const(tmp).type().id() == ID_array && expr.type().id() == ID_array) ||
as_const(tmp).type() == expr.type(),
tmp.pretty(),
(as_const(simplify_node_result.expr).type().id() == ID_array &&
expr.type().id() == ID_array) ||
as_const(simplify_node_result.expr).type() == expr.type(),
simplify_node_result.expr.pretty(),
expr.pretty());

#ifdef USE_CACHE
// save in cache
cache_result.first->second = tmp;
cache_result.first->second = simplify_node_result.expr;
#endif

return std::move(tmp);
return simplify_node_result;
}
}

Expand Down
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