rely on is_sat fallback for failed repair-up, add separate file for WIP on lookahead.

src/ast/sls/sls_bv_lookahead.h

@@ -0,0 +1,53 @@
+/*++
+Copyright (c) 2024 Microsoft Corporation
+
+Module Name:
+
+    sls_bv_lookahead.h
+
+Abstract:
+
+    Lookahead solver for BV, modeled after sls_engine/sls_tracker/sls_evaluator.
+
+Author:
+
+    Nikolaj Bjorner (nbjorner) 2024-12-26
+
+--*/
+#pragma once
+
+#include "ast/bv_decl_plugin.h"
+#include "ast/sls/sls_context.h"
+
+namespace sls {
+    class bv_eval;
+    class bv_valuation;
+    class bvect;
+
+    class bv_lookahead {
+        bv_util bv;
+        bv_eval& m_ev;
+        context& ctx;
+        ast_manager& m;
+
+        ptr_vector<expr> m_restore;
+        vector<ptr_vector<expr>> m_update_stack;
+        expr_mark m_on_restore;
+
+        bv_valuation& wval(expr* e) const;
+
+        void insert_update_stack(expr* e);
+        bool insert_update(expr* e);
+        
+        void restore_lookahead();
+
+        double lookahead(expr* e, bvect const& new_value);
+
+    public:
+        bv_lookahead(bv_eval& ev);
+        bool on_restore(expr* e) const;
+
+        bool try_repair_down(expr* e);
+
+    };
+}