added derivative support for (str.to_re (str.from_int ...)) #5431
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| @@ -3339,6 +3339,26 @@ expr_ref seq_rewriter::mk_derivative_rec(expr* ele, expr* r) { | |||
| //while mk_empty() = [], because deriv(epsilon) = [] = nothing | |||
| return mk_empty(); | |||
| } | |||
| else if (str().is_itos(r1, r2)) | |||
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I don't see how it fixes the underlying issue. The default behavior is to return a derivative expression. It should be sound no matter what it is applied to. Adding this code just bypasses the default case so it seems to mask the bug, not outright address it for other scenarios. Suppose I introduce an uninterpreted function that has the same effect as itos. This code would go to the default case.
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| tl = str().mk_substr(r1, m_autil.mk_int(1), m_autil.mk_sub(str().mk_length(r1), m_autil.mk_int(1))); | ||
| //if ((isdigit ele) and (ele = (hd r1))) then (to_re (tl r1)) else [] | ||
| result = re_and(result, re().mk_to_re(tl)); |
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re_and already performs constant folding when the condition is true/false. So having the caller perform constant folding is at best a micro-optimization with the effect of making the code more elaborate.
I
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This fixes an unsound unsat result in one case discussed in issue #5140
involving the use of (str.to_re (str.from_int (str.len x))) where x is uninterpreted.