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#7739 optimization

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add simplification rule for at(x, offset) = ""

Introducing j just postpones some rewrites that prevent useful simplifications. Z3 already uses common sub-expressions.
The example highlights some opportunities for simplification, noteworthy at(..) = "".
The example is solved in both versions after adding this simplification.
This commit is contained in:
Nikolaj Bjorner 2025-07-26 14:02:34 -07:00
parent 8e1a528796
commit 1f8b08108c
1 changed files with 6 additions and 0 deletions
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6
src/ast/rewriter/seq_rewriter.cpp
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@ -6021,6 +6021,12 @@ bool seq_rewriter::reduce_eq_empty(expr* l, expr* r, expr_ref& result) {
result = m_autil.mk_lt(s, zero());
return true;
}
// at(s, offset) = "" <=> len(s) <= offset or offset < 0
if (str().is_at(r, s, offset)) {
expr_ref len_s(str().mk_length(s), m());
result = m().mk_or(m_autil.mk_le(len_s, offset), m_autil.mk_lt(offset, zero()));
return true;
}
return false;
}