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81 lines
2.7 KiB
C++
81 lines
2.7 KiB
C++
/*++
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Copyright (c) 2018 Microsoft Corporation
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Module Name:
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recfun_rewriter.cpp
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Abstract:
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Rewriter recursive function applications to values
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Author:
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Nikolaj Bjorner (nbjorner) 2020-04-26
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--*/
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#include "ast/rewriter/recfun_rewriter.h"
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#include "ast/rewriter/var_subst.h"
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#include "ast/datatype_decl_plugin.h"
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#include "ast/for_each_expr.h"
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br_status recfun_rewriter::mk_app_core(func_decl * f, unsigned num_args, expr * const * args, expr_ref & result) {
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if (m_rec.is_defined(f) && num_args > 0) {
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if (!m_rec.has_def(f))
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return BR_FAILED;
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recfun::def const& d = m_rec.get_def(f);
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if (!d.get_rhs())
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return BR_FAILED;
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auto r = d.get_rhs();
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bool safe_to_subst = true;
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for (unsigned i = 0; i < num_args; ++i)
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if (!m.is_value(args[i]))
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safe_to_subst = false;
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// check if there is an argument that is a constructor
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// such that the recursive function can be partially evaluated.
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// at most one kind of accessor is allowed to prevent recursive
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// patterns that reconstruct the argument indirectly.
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// This can be relaxed to omitting at least one accessor, and probably other patterns.
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if (!safe_to_subst && !has_quantifiers(r)) {
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datatype::util u(m);
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auto is_decreasing = [&](unsigned i) {
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bool is_dec = true;
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unsigned idx = num_args - i - 1;
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func_decl* dec_fun = nullptr;
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for (auto t : subterms::all(expr_ref(r, m))) {
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if (is_app(t) && any_of(*to_app(t), [&](expr* e) { return is_var(e) && to_var(e)->get_idx() == idx; })) {
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if (!u.is_accessor(t) && !u.is_is(t) && !u.is_recognizer(t))
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is_dec = false;
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else if (u.is_accessor(t) && dec_fun && to_app(t)->get_decl() != dec_fun)
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is_dec = false;
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else if (u.is_accessor(t))
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dec_fun = to_app(t)->get_decl();
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}
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}
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return is_dec;
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};
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for (unsigned i = 0; i < num_args; ++i) {
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auto arg = args[i];
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if (u.is_constructor(arg) && is_decreasing(i)) {
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safe_to_subst = true;
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break;
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}
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}
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}
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if (safe_to_subst) {
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var_subst sub(m);
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result = sub(d.get_rhs(), num_args, args);
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return BR_REWRITE_FULL;
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}
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return BR_FAILED;
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}
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else
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return BR_FAILED;
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}
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