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Add separate overflow expr classes #6744

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Merged
merged 17 commits into from
Mar 23, 2022
Merged

Add separate overflow expr classes #6744

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19db9a0
Add `binary_predicate_exprt` sub classes
thomasspriggs Mar 7, 2022
0f6ae1c
Add `binary_predicate_exprt` sub class unit tests
thomasspriggs Mar 22, 2022
5d7c21c
Add invariant on kind used to construct `binary_overflow_exprt`
thomasspriggs Mar 22, 2022
ce025e1
Use `mult_overflow_exprt` in `boolbvt::convert_overflow`
thomasspriggs Mar 22, 2022
defc6d4
Use `shl_overflow_exprt` in `boolbvt::convert_overflow`
thomasspriggs Mar 22, 2022
0d36c43
Use `plus/minus_overflow_exprt` in `boolbvt::convert_overflow`
thomasspriggs Mar 22, 2022
636ffa8
Use `binary_overflow_exprt` in `expr2ct::convert_with_precedence`
thomasspriggs Mar 22, 2022
d4b17bd
Use `binary_overflow_exprt` in `boolbvt::convert_rest`
thomasspriggs Mar 22, 2022
533a902
Use `plus/minus_overflow_exprt` in `smt2_convt`
thomasspriggs Mar 22, 2022
fdc0fc8
Use `mult_overflow_exprt` in `smt2_convt`
thomasspriggs Mar 22, 2022
12a4451
Use `minus_overflow_exprt` in `simplify_overflow_binary`
thomasspriggs Mar 22, 2022
4e3e8b9
Use `mult_overflow_exprt` in `simplify_overflow_binary`
thomasspriggs Mar 22, 2022
24c9da7
Use `plus_overflow_exprt` in `simplify_overflow_binary`
thomasspriggs Mar 22, 2022
7936b57
Use `shl_overflow_exprt` in `simplify_overflow_binary`
thomasspriggs Mar 22, 2022
98c80dc
Use `binary_overflow_exprt` in `simplify_exprt::simplify_node`
thomasspriggs Mar 22, 2022
631aeb4
Add `unary_minus_overflow_exprt`
thomasspriggs Mar 22, 2022
c0f179c
Use `unary_minus_overflow_exprt`
thomasspriggs Mar 22, 2022
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44 changes: 26 additions & 18 deletions src/solvers/flattening/boolbv_overflow.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -13,25 +13,33 @@ Author: Daniel Kroening, [email protected]

literalt boolbvt::convert_overflow(const exprt &expr)
{
if(expr.id()==ID_overflow_plus ||
expr.id()==ID_overflow_minus)
const auto plus_or_minus_conversion =
[&](
const binary_overflow_exprt &overflow_expr,
const std::function<literalt(
bv_utilst *, const bvt &, const bvt &, bv_utilst::representationt)>
&bv_util_overflow) {
const bvt &bv0 = convert_bv(overflow_expr.lhs());
const bvt &bv1 = convert_bv(overflow_expr.rhs());

if(bv0.size() != bv1.size())
return SUB::convert_rest(expr);

bv_utilst::representationt rep =
overflow_expr.lhs().type().id() == ID_signedbv
? bv_utilst::representationt::SIGNED
: bv_utilst::representationt::UNSIGNED;

return bv_util_overflow(&bv_utils, bv0, bv1, rep);
};
if(
const auto plus_overflow = expr_try_dynamic_cast<plus_overflow_exprt>(expr))
{
const auto &overflow_expr = to_binary_expr(expr);

const bvt &bv0 = convert_bv(overflow_expr.lhs());
const bvt &bv1 = convert_bv(overflow_expr.rhs());

if(bv0.size()!=bv1.size())
return SUB::convert_rest(expr);

bv_utilst::representationt rep =
overflow_expr.lhs().type().id() == ID_signedbv
? bv_utilst::representationt::SIGNED
: bv_utilst::representationt::UNSIGNED;

return expr.id()==ID_overflow_minus?
bv_utils.overflow_sub(bv0, bv1, rep):
bv_utils.overflow_add(bv0, bv1, rep);
return plus_or_minus_conversion(*plus_overflow, &bv_utilst::overflow_add);
}
if(const auto minus = expr_try_dynamic_cast<minus_overflow_exprt>(expr))
{
return plus_or_minus_conversion(*minus, &bv_utilst::overflow_sub);
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I don't think the lambda helps readability here. I'd perhaps favour two branches with almost identical code, or else a slightly larger refactor: all the branches in boolbvt::convert_overflow need to convert the operands, perhaps also need to determine signed/unsigned representation. And we might opt to be consistent in whether we support (multiply) or don't support (other cases) operands of different width. (I have no idea why we would support them.)

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I agree that the more ideal refactor would be to remove more of the duplication between all of the branches here. However given that I have approvals on this PR and I have other work which is based on top of this, I am going to merge this as-is and then come back to refactoring boolbvt::convert_overflow as a follow-up PR. That way the larger refactor can be considered in isolation.

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Thinking about mismatched operand widths, I think there is the potential for a simpler/smaller formula for multiplying two operands of mismatched but shorter widths instead of 2 operands of matched but larger widths due to being extended to match. Any potential benefits to this are speculation on my part and it seems like a case which may be rare in source code or even always eliminated by implicit type casts before we reach this stage.

}
else if(
const auto mult_overflow = expr_try_dynamic_cast<mult_overflow_exprt>(expr))
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