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CONTRACTS: ignore __CPROVER_dead_object assignments #8554

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merged 2 commits into from
Jan 3, 2025
Merged

CONTRACTS: ignore __CPROVER_dead_object assignments #8554

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39f9c87
CONTRACTS: don't instrument `__CPROVER_dead_object` anymore.
Jan 3, 2025
b6bae90
Fix dangling doxygen ref.
Jan 3, 2025
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62 changes: 0 additions & 62 deletions src/goto-instrument/contracts/dynamic-frames/dfcc_instrument.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -735,31 +735,6 @@ void dfcc_instrumentt::instrument_lhs(
insert_before_swap_and_advance(goto_program, target, payload);
}

/// Checks if lhs is the `dead_object`, and if the rhs
/// is an `if_exprt(nondet, ptr, dead_object)` expression.
/// Returns `ptr` if the pattern was matched, nullptr otherwise.
std::optional<exprt>
dfcc_instrumentt::is_dead_object_update(const exprt &lhs, const exprt &rhs)
{
if(
lhs.id() == ID_symbol &&
to_symbol_expr(lhs).get_identifier() == CPROVER_PREFIX "dead_object" &&
rhs.id() == ID_if)
{
// only handle `if_exprt(nondet, ptr, dead_object)`
auto &if_expr = to_if_expr(rhs);
if(
if_expr.cond().id() == ID_side_effect &&
to_side_effect_expr(if_expr.cond()).get_statement() == ID_nondet &&
if_expr.false_case() == lhs)
{
return if_expr.true_case();
}
}

return {};
}

void dfcc_instrumentt::instrument_assign(
const irep_idt &function_id,
goto_programt::targett &target,
Expand All @@ -775,43 +750,6 @@ void dfcc_instrumentt::instrument_assign(
if(cfg_info.must_check_lhs(target))
instrument_lhs(function_id, target, lhs, goto_program, cfg_info);

// handle dead_object updates (created by __builtin_alloca for instance)
// Remark: we do not really need to track this deallocation since the default
// CBMC checks are already able to detect writes to DEAD objects
const auto dead_ptr = is_dead_object_update(lhs, rhs);
if(dead_ptr.has_value())
{
// ```
// ASSIGN dead_object := if_exprt(nondet, ptr, dead_object);
// ----
// IF !write_set GOTO skip_target;
// CALL record_deallocated(write_set, ptr);
// skip_target: SKIP;
// ```

// step over the instruction
target++;

goto_programt payload;

auto goto_instruction = payload.add(goto_programt::make_incomplete_goto(
dfcc_utilst::make_null_check_expr(write_set), target_location));

payload.add(goto_programt::make_function_call(
library.write_set_record_dead_call(
write_set, dead_ptr.value(), target_location),
target_location));

auto label_instruction =
payload.add(goto_programt::make_skip(target_location));
goto_instruction->complete_goto(label_instruction);

insert_before_swap_and_advance(goto_program, target, payload);

// step back
target--;
}

// is the rhs expression a side_effect("allocate") expression ?
if(rhs.id() == ID_side_effect && rhs.get(ID_statement) == ID_allocate)
{
Expand Down
9 changes: 0 additions & 9 deletions src/goto-instrument/contracts/dynamic-frames/dfcc_instrument.h
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Original file line number Diff line number Diff line change
Expand Up @@ -283,17 +283,8 @@ class dfcc_instrumentt
goto_programt &goto_program,
dfcc_cfg_infot &cfg_info);

/// Checks if \p lhs is the `dead_object`, and if \p rhs
/// is an `if_exprt(nondet, ptr, dead_object)` expression.
/// Returns a pointer to the `ptr` expression if the pattern was matched,
/// returns `nullptr` otherwise.
std::optional<exprt>
is_dead_object_update(const exprt &lhs, const exprt &rhs);

/// Instrument the \p lhs of an `ASSIGN lhs := rhs` instruction by
/// adding an inclusion check of \p lhs in \p write_set.
/// If \ref is_dead_object_update returns a successful match, the matched
/// pointer expression is removed from \p write_set.
/// If \p rhs is a `side_effect_expr(ID_allocate)`, the allocated pointer gets
/// added to the \p write_set.
/// \pre \p target points to an `ASSIGN` instruction.
Expand Down
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