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Introduce value-set supported simplifier for goto-symex #8642

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Introduce value-set supported simplifier for goto-symex #8642

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f214ac4
Introduce value-set supported simplifier for goto-symex
tautschnig May 27, 2025
ae46889
Use simplify_expr_with_value_sett across goto-symex
tautschnig May 27, 2025
6489c32
Simplify pointer_offset using value set
tautschnig May 28, 2025
77d0e0e
Simplify equal/not-equal over pointer_object expressions using value set
tautschnig May 30, 2025
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7 changes: 7 additions & 0 deletions regression/cbmc/pointer-offset-02/main.c
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Original file line number Diff line number Diff line change
@@ -0,0 +1,7 @@
#include <stdlib.h>

int main()
{
int *p = malloc(sizeof(int));
__CPROVER_assert(__CPROVER_POINTER_OFFSET(p) == 0, "");
}
9 changes: 9 additions & 0 deletions regression/cbmc/pointer-offset-02/test.desc
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@@ -0,0 +1,9 @@
CORE
main.c
--verbosity 8
^Generated \d+ VCC\(s\), 0 remaining after simplification$
^VERIFICATION SUCCESSFUL$
^EXIT=0$
^SIGNAL=0$
--
^warning: ignoring
55 changes: 55 additions & 0 deletions src/goto-symex/simplify_expr_with_value_set.cpp
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Expand Up @@ -154,3 +154,58 @@ simplify_exprt::resultt<> simplify_expr_with_value_sett::simplify_inequality(
else
return unchanged(expr);
}

simplify_exprt::resultt<>
simplify_expr_with_value_sett::simplify_pointer_offset(
Comment on lines +230 to +231
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I'd include a header comment here with your commit description

When all candidates in the value set have the same offset we can replace
a pointer_offset expression by the offset value found in the value set.

Since there is only one simplification applied. This is nitpick since one may infer from the code.

const pointer_offset_exprt &expr)
{
const exprt &ptr = expr.pointer();

if(ptr.type().id() != ID_pointer)
return unchanged(expr);

const ssa_exprt *ssa_symbol_expr = expr_try_dynamic_cast<ssa_exprt>(ptr);

if(!ssa_symbol_expr)
return simplify_exprt::simplify_pointer_offset(expr);

ssa_exprt l1_expr{*ssa_symbol_expr};
l1_expr.remove_level_2();
const std::vector<exprt> value_set_elements =
value_set.get_value_set(l1_expr, ns);

std::optional<exprt> offset;

for(const auto &value_set_element : value_set_elements)
{
if(
value_set_element.id() == ID_unknown ||
value_set_element.id() == ID_invalid ||
is_failed_symbol(
to_object_descriptor_expr(value_set_element).root_object()) ||
to_object_descriptor_expr(value_set_element).offset().id() == ID_unknown)
{
offset.reset();
break;
}

exprt this_offset = to_object_descriptor_expr(value_set_element).offset();
if(
this_offset.id() == ID_unknown ||
(offset.has_value() && this_offset != *offset))
{
offset.reset();
break;
}
else if(!offset.has_value())
{
offset = this_offset;
}
}

if(!offset.has_value())
return simplify_exprt::simplify_pointer_offset(expr);

return changed(
simplify_rec(typecast_exprt::conditional_cast(*offset, expr.type())));
}
2 changes: 2 additions & 0 deletions src/goto-symex/simplify_expr_with_value_set.h
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Expand Up @@ -26,6 +26,8 @@ class simplify_expr_with_value_sett : public simplify_exprt

[[nodiscard]] resultt<>
simplify_inequality(const binary_relation_exprt &) override;
[[nodiscard]] resultt<>
simplify_pointer_offset(const pointer_offset_exprt &) override;

protected:
const value_sett &value_set;
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3 changes: 2 additions & 1 deletion src/util/simplify_expr_class.h
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Expand Up @@ -202,7 +202,8 @@ class simplify_exprt
[[nodiscard]] resultt<>
simplify_dereference_preorder(const dereference_exprt &);
[[nodiscard]] resultt<> simplify_address_of(const address_of_exprt &);
[[nodiscard]] resultt<> simplify_pointer_offset(const pointer_offset_exprt &);
[[nodiscard]] virtual resultt<>
simplify_pointer_offset(const pointer_offset_exprt &);
[[nodiscard]] resultt<> simplify_bswap(const bswap_exprt &);
[[nodiscard]] resultt<> simplify_isinf(const unary_exprt &);
[[nodiscard]] resultt<> simplify_isnan(const unary_exprt &);
Expand Down