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diff --git a/rcc-legacy/include/rcc/loopinfo.h b/rcc-legacy/include/rcc/loopinfo.h
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+++ b/rcc-legacy/include/rcc/loopinfo.h
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+/* Source code for RCC-Legacy.
+   Copyright (C) 2026 Richard Qin
+
+This file is part of RCC.
+
+RCC is free software; you can redistribute it and/or modify it under
+the terms of the GNU General Public License as published by the Free
+Software Foundation; either version 3, or (at your option) any later
+version.
+
+RCC is distributed in the hope that it will be useful, but WITHOUT ANY
+WARRANTY; without even the implied warranty of MERCHANTABILITY or
+FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+for more details.
+
+You should have received a copy of the GNU General Public License
+along with RCC; see the file LICENSE.  If not see
+<http://www.gnu.org/licenses/>.  */
+
+/// @file loopinfo.h
+/// @brief Natural loop and constant BIV identification.
+
+#pragma once
+
+#include "rcc/all.h"
+
+#include <unordered_set>
+#include <vector>
+
+namespace rcc {
+
+struct Loop {
+    Blk* header;
+    Blk* preheader;
+    Blk* latch;
+    std::vector<Blk*> body;             // Includes header / latch
+    std::unordered_set<uint> body_bid;  // Set of b->id in body, used for tmp.bid lookup
+};
+
+/// Constant Basic Induction Variable.
+struct Biv {
+    Ref to;        // header phi.to
+    int cls;       // phi cls
+    int64_t init;  // Preheader constant
+    int64_t step;  // Constant step of Oadd at latch, != 0
+};
+
+void find_loops(Fn*, std::vector<Loop>&);
+void detect_bivs(Fn*, const Loop&, std::vector<Biv>&);
+
+/// Decode CBits constant Ref (integer). Returns false for CAddr / float / non-RCon.
+bool ref_is_const(Fn*, Ref, int64_t& out);
+
+/// Get defining Ins via Tmp::def. Returns nullptr for non-RTmp or out of bounds.
+Ins* def_ins(Fn*, Ref);
+
+/// Canonical pointer IV after LSR.
+struct PointerIV {
+    Ref phi_to;
+    Ref base;
+    Ref next;
+    int64_t step;
+};
+
+/// Identify pointer IV on header phi. Returns false on failure.
+bool pick_pointer_iv(Fn*, const Loop&, Phi*, PointerIV*);
+
+/// Match pointer termination condition against pointer IV.
+bool check_exit_cmp(Fn*, const Loop&, Ref p, Ref* end_out, Blk** after_out);
+
+/// Check if any def inside the loop is used by outside users.
+bool has_outside_use(Fn*, const Loop&);
+
+}  // namespace rcc