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Pointer subtraction in back-end: no need for bounds checking #8497

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Merged
merged 1 commit into from
Nov 7, 2024
Merged

Pointer subtraction in back-end: no need for bounds checking #8497

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6 changes: 3 additions & 3 deletions regression/cbmc/Pointer_difference2/test.desc
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Original file line number Diff line number Diff line change
Expand Up @@ -5,11 +5,11 @@ main.c
^\[main.pointer.1\] line 8 same object violation in array - other_array: FAILURE$
^\[main.assertion.2\] line 11 undefined behavior: FAILURE$
^\[main.assertion.3\] line 13 undefined behavior: FAILURE$
^\[main.assertion.7\] line 26 end plus 2 is nondet: FAILURE$
^\[main.assertion.7\] line 26 end plus 2 is nondet: (UNKNOWN|FAILURE)$
^\[main.pointer_arithmetic.\d+\] line 26 pointer relation: pointer outside object bounds in p: FAILURE$
^\[main.assertion.8\] line 28 end plus 2 is nondet: FAILURE$
^\[main.assertion.8\] line 28 end plus 2 is nondet: (UNKNOWN|FAILURE)$
^\[main.pointer_arithmetic.\d+\] line 28 pointer relation: pointer outside object bounds in p: FAILURE$
^\*\* 9 of \d+ failed
^\*\* [789] of \d+ failed
^VERIFICATION FAILED$
^EXIT=10$
^SIGNAL=0$
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35 changes: 2 additions & 33 deletions src/solvers/flattening/bv_pointers.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -665,39 +665,8 @@ bvt bv_pointerst::convert_bitvector(const exprt &expr)
difference, element_size_bv, bv_utilst::representationt::SIGNED);
}

// test for null object (integer constants)
const exprt null_object = ::null_object(minus_expr.lhs());
literalt in_bounds = convert(null_object);

if(!in_bounds.is_true())
{
// compute the object size (again, possibly using cached results)
const exprt object_size = ::object_size(minus_expr.lhs());
const bvt object_size_bv =
bv_utils.zero_extension(convert_bv(object_size), width);

const literalt lhs_in_bounds = prop.land(
!bv_utils.sign_bit(lhs_offset),
bv_utils.rel(
lhs_offset,
ID_le,
object_size_bv,
bv_utilst::representationt::UNSIGNED));

const literalt rhs_in_bounds = prop.land(
!bv_utils.sign_bit(rhs_offset),
bv_utils.rel(
rhs_offset,
ID_le,
object_size_bv,
bv_utilst::representationt::UNSIGNED));

in_bounds =
prop.lor(in_bounds, prop.land(lhs_in_bounds, rhs_in_bounds));
}

prop.l_set_to_true(prop.limplies(
prop.land(same_object_lit, in_bounds), bv_utils.equal(difference, bv)));
prop.l_set_to_true(
prop.limplies(same_object_lit, bv_utils.equal(difference, bv)));
}

return bv;
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