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Simplify byte extract: fix unconditional read from optional values #7376

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Merged
merged 1 commit into from
Nov 23, 2022
Merged

Simplify byte extract: fix unconditional read from optional values #7376

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20 changes: 12 additions & 8 deletions src/util/simplify_expr.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1680,15 +1680,19 @@ simplify_exprt::simplify_byte_extract(const byte_extract_exprt &expr)
{
return op_byte_update.value();
}
else if(
el_size.has_value() &&
*el_size <= pointer_offset_bits(op_byte_update.value().type(), ns))
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Huh.. wasn't there even a compiler warning on that?

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This was invoking this piece of code:
https://github.com/diffblue/cbmc/blob/8848ad878da46bbcd0cedad634e235e6faf8cb17/src/nonstd/optional.hpp#L997..L1000
which will return false when the optionalt doesn't have a value.

else if(el_size.has_value())
{
auto tmp = expr;
tmp.op() = op_byte_update.value();
tmp.offset() = from_integer(0, expr.offset().type());
const auto update_bits_opt =
pointer_offset_bits(op_byte_update.value().type(), ns);

if(update_bits_opt.has_value() && *el_size <= *update_bits_opt)
{
auto tmp = expr;
tmp.op() = op_byte_update.value();
tmp.offset() = from_integer(0, expr.offset().type());

return changed(simplify_byte_extract(tmp)); // recursive call
return changed(simplify_byte_extract(tmp)); // recursive call
}
}
}

Expand All @@ -1706,7 +1710,7 @@ simplify_exprt::simplify_byte_extract(const byte_extract_exprt &expr)
{
const byte_update_exprt &bu = to_byte_update_expr(expr.op());
const auto update_offset = numeric_cast<mp_integer>(bu.offset());
if(update_offset.has_value())
if(el_size.has_value() && update_offset.has_value())
{
if(
*offset * expr.get_bits_per_byte() + *el_size <=
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