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simplify_byte_extract: avoid unnecessary calls to has_subtype #7712

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Merged
merged 1 commit into from
May 17, 2023
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simplify_byte_extract: avoid unnecessary calls to has_subtype #7712

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65 changes: 34 additions & 31 deletions src/util/simplify_expr.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1831,41 +1831,44 @@ simplify_exprt::simplify_byte_extract(const byte_extract_exprt &expr)
const auto bits =
expr2bits(expr.op(), expr.id() == ID_byte_extract_little_endian, ns);

// make sure we don't lose bits with structs containing flexible array members
const bool struct_has_flexible_array_member = has_subtype(
expr.type(),
[&](const typet &type) {
if(type.id() != ID_struct && type.id() != ID_struct_tag)
return false;

const struct_typet &st = to_struct_type(ns.follow(type));
const auto &comps = st.components();
if(comps.empty() || comps.back().type().id() != ID_array)
return false;

if(comps.back().type().get_bool(ID_C_flexible_array_member))
return true;

const auto size =
numeric_cast<mp_integer>(to_array_type(comps.back().type()).size());
return !size.has_value() || *size <= 1;
},
ns);
if(
bits.has_value() &&
mp_integer(bits->size()) >= *el_size + *offset * expr.get_bits_per_byte() &&
!struct_has_flexible_array_member)
{
std::string bits_cut = std::string(
bits.value(),
numeric_cast_v<std::size_t>(*offset * expr.get_bits_per_byte()),
numeric_cast_v<std::size_t>(*el_size));
mp_integer(bits->size()) >= *el_size + *offset * expr.get_bits_per_byte())
{
// make sure we don't lose bits with structs containing flexible array
// members
const bool struct_has_flexible_array_member = has_subtype(
expr.type(),
[&](const typet &type) {
if(type.id() != ID_struct && type.id() != ID_struct_tag)
return false;

const struct_typet &st = to_struct_type(ns.follow(type));
const auto &comps = st.components();
if(comps.empty() || comps.back().type().id() != ID_array)
return false;

if(comps.back().type().get_bool(ID_C_flexible_array_member))
return true;

const auto size =
numeric_cast<mp_integer>(to_array_type(comps.back().type()).size());
return !size.has_value() || *size <= 1;
},
ns);
if(!struct_has_flexible_array_member)
{
std::string bits_cut = std::string(
bits.value(),
numeric_cast_v<std::size_t>(*offset * expr.get_bits_per_byte()),
numeric_cast_v<std::size_t>(*el_size));

auto tmp = bits2expr(
bits_cut, expr.type(), expr.id() == ID_byte_extract_little_endian, ns);
auto tmp = bits2expr(
bits_cut, expr.type(), expr.id() == ID_byte_extract_little_endian, ns);

if(tmp.has_value())
return std::move(*tmp);
if(tmp.has_value())
return std::move(*tmp);
}
}

// push byte extracts into struct or union expressions, just like
Expand Down