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byte_extract lowering of string constants [blocks: #2068] #4186

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Merged
tautschnig merged 1 commit into from
Feb 15, 2019
Merged

byte_extract lowering of string constants [blocks: #2068] #4186

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21 changes: 21 additions & 0 deletions src/solvers/lowering/byte_operators.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -15,6 +15,7 @@ Author: Daniel Kroening, kroening@kroening.com
#include <util/pointer_offset_size.h>
#include <util/replace_symbol.h>
#include <util/simplify_expr.h>
#include <util/string_constant.h>

#include "flatten_byte_extract_exceptions.h"

Expand Down Expand Up @@ -275,6 +276,26 @@ static exprt unpack_rec(
ns,
unpack_byte_array);
}
else if(src.id() == ID_string_constant)
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@smowton smowton Feb 14, 2019

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I might be wrong, but I think these are not used by Java, so the commit message may need amending

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@tautschnig tautschnig Feb 14, 2019

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Amended to not have that unnecessary restriction, but I do see results of git grep string_constantt in jbmc/ as well...

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@smowton smowton Feb 14, 2019

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They are used for input and output steps only; the Java bytecode parser makes them to describe string literals, but those are later transformed into references to constant java.lang.String instances, so there are no free-floating constants in the same way as there are in C.

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@tautschnig tautschnig Feb 14, 2019

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Ah, ok! I guess it must have been some C code where I had seen them in the wild.

{
return unpack_rec(
to_string_constant(src).to_array_expr(),
little_endian,
offset_bytes,
max_bytes,
ns,
unpack_byte_array);
}
else if(src.id() == ID_constant && src.type().id() == ID_string)
{
return unpack_rec(
string_constantt(to_constant_expr(src).get_value()).to_array_expr(),
little_endian,
offset_bytes,
max_bytes,
ns,
unpack_byte_array);
}
else if(src.type().id()!=ID_empty)
{
// a basic type; we turn that into extractbits while considering
Expand Down
30 changes: 30 additions & 0 deletions unit/solvers/lowering/byte_operators.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -21,6 +21,7 @@
#include <util/simplify_expr.h>
#include <util/simplify_expr_class.h>
#include <util/std_types.h>
#include <util/string_constant.h>
#include <util/symbol_table.h>

SCENARIO("byte_extract_lowering", "[core][solvers][lowering][byte_extract]")
Expand Down Expand Up @@ -90,6 +91,35 @@ SCENARIO("byte_extract_lowering", "[core][solvers][lowering][byte_extract]")
}
}

GIVEN("A a byte_extract from a string constant")
{
string_constantt s("ABCD");
const byte_extract_exprt be1(
ID_byte_extract_little_endian,
s,
from_integer(1, index_type()),
unsignedbv_typet(16));

THEN("byte_extract lowering yields the expected value")
{
const exprt lower_be1 = lower_byte_extract(be1, ns);

REQUIRE(!has_subexpr(lower_be1, ID_byte_extract_little_endian));
REQUIRE(lower_be1.type() == be1.type());
REQUIRE(
lower_be1 == from_integer((int{'C'} << 8) + 'B', unsignedbv_typet(16)));

byte_extract_exprt be2 = be1;
be2.id(ID_byte_extract_big_endian);
const exprt lower_be2 = lower_byte_extract(be2, ns);

REQUIRE(!has_subexpr(lower_be2, ID_byte_extract_big_endian));
REQUIRE(lower_be2.type() == be2.type());
REQUIRE(
lower_be2 == from_integer((int{'B'} << 8) + 'C', unsignedbv_typet(16)));
}
}

GIVEN("A collection of types")
{
unsignedbv_typet u8(8);
Expand Down