diff --git a/compiler/loop.lisp b/compiler/loop.lisp
new file mode 100644
index 0000000000000000000000000000000000000000..f160e184312a53512b7180343993fa77ee3b50a8
--- /dev/null
+++ b/compiler/loop.lisp
@@ -0,0 +1,217 @@
+;;; -*- Package: C -*-
+;;;
+;;; **********************************************************************
+;;; This code was written as part of the CMU Common Lisp project at
+;;; Carnegie Mellon University, and has been placed in the public domain.
+;;;
+(ext:file-comment
+  "$Header: /Volumes/share2/src/cmucl/cvs2git/cvsroot/src/compiler/loop.lisp,v 1.1 2004/11/05 21:57:25 rtoy Rel $")
+;;; **********************************************************************
+;;;
+;;; Stuff to annotate the flow graph with information about the loops in it.
+;;;
+;;; Written by Rob MacLachlan
+(in-package "C")
+
+;;; FIND-DOMINATORS  --  Internal
+;;;
+;;; Find the set of blocks that dominates each block in COMPONENT.  We
+;;; assume that the DOMINATORS for each block is initially NIL, which
+;;; serves to represent the set of all blocks.  If a block is not
+;;; reachable from an entry point, then its dominators will still be
+;;; NIL when we are done.
+(defun find-dominators (component)
+  (let ((head (loop-head (component-outer-loop component)))
+	changed)
+    (let ((set (make-sset)))
+      (sset-adjoin head set)
+      (setf (block-dominators head) set))
+    (loop
+     (setq changed nil)
+     (do-blocks (block component :tail)
+       (let ((dom (block-dominators block)))
+	 (when dom (sset-delete block dom))
+	 (dolist (pred (block-pred block))
+	   (let ((pdom (block-dominators pred)))
+	     (when pdom
+	       (if dom
+		   (when (sset-intersection dom pdom)
+		     (setq changed t))
+		   (setq dom (copy-sset pdom) changed t)))))	 
+	 (setf (block-dominators block) dom)
+	 (when dom (sset-adjoin block dom))))
+     (unless changed (return)))))
+
+
+;;; DOMINATES-P  --  Internal
+;;;
+;;;    Return true if BLOCK1 dominates BLOCK2, false otherwise.
+(defun dominates-p (block1 block2)
+  (let ((set (block-dominators block2)))
+    (if set
+	(sset-member block1 set)
+	t)))
+
+;;; LOOP-ANALYZE  --  Interface
+;;;
+;;; Set up the LOOP structures which describe the loops in the flow
+;;; graph for COMPONENT.  We NIL out any existing loop information,
+;;; and then scan through the blocks looking for blocks which are the
+;;; destination of a retreating edge: an edge that goes backward in
+;;; the DFO.  We then create LOOP structures to describe the loops
+;;; that have those blocks as their heads.  If find the head of a
+;;; strange loop, then we do some graph walking to find the other
+;;; segments in the strange loop.  After we have found the loop
+;;; structure, we walk it to initialize the block lists.
+(defun loop-analyze (component)
+  (let ((loop (component-outer-loop component)))
+    (do-blocks (block component :both)
+      (setf (block-loop block) nil))
+    (setf (loop-inferiors loop) ())
+    (setf (loop-blocks loop) nil)
+    (do-blocks (block component)
+      (let ((number (block-number block)))
+	(dolist (pred (block-pred block))
+	  (when (<= (block-number pred) number)
+	    (when (note-loop-head block component)
+	      (clear-flags component)
+	      (setf (block-flag block) :good)
+	      (dolist (succ (block-succ block))
+		(find-strange-loop-blocks succ block))
+	      (find-strange-loop-segments block component))
+	    (return)))))
+    (find-loop-blocks (component-outer-loop component))))
+
+
+;;; FIND-LOOP-BLOCKS  --  Internal
+;;;
+;;; This function initializes the block lists for LOOP and the loops
+;;; nested within it.  We recursively descend into the loop nesting
+;;; and place the blocks in the appropriate loop on the way up.  When
+;;; we are done, we scan the blocks looking for exits.  An exit is
+;;; always a block that has a successor which doesn't have a LOOP
+;;; assigned yet, since the target of the exit must be in a superior
+;;; loop.
+;;;
+;;; We find the blocks by doing a forward walk from the head of the
+;;; loop and from any exits of nested loops.  The walks from inferior
+;;; loop exits are necessary because the walks from the head terminate
+;;; when they encounter a block in an inferior loop.
+(defun find-loop-blocks (loop)
+  (dolist (sub-loop (loop-inferiors loop))
+    (find-loop-blocks sub-loop))
+
+  (find-blocks-from-here (loop-head loop) loop)
+  (dolist (sub-loop (loop-inferiors loop))
+    (dolist (exit (loop-exits sub-loop))
+      (dolist (succ (block-succ exit))
+	(find-blocks-from-here succ loop))))
+  
+  (collect ((exits))
+    (dolist (sub-loop (loop-inferiors loop))
+      (dolist (exit (loop-exits sub-loop))
+	(dolist (succ (block-succ exit))
+	  (unless (block-loop succ)
+	    (exits exit)
+	    (return)))))
+    
+    (do ((block (loop-blocks loop) (block-loop-next block)))
+	((null block))
+      (dolist (succ (block-succ block))
+	(unless (block-loop succ)
+	  (exits block)
+	  (return))))    
+    (setf (loop-exits loop) (exits))))
+
+
+;;; FIND-BLOCKS-FROM-HERE  --  Internal
+;;;
+;;; This function does a graph walk to find the blocks directly within
+;;; LOOP that can be reached by a forward walk from BLOCK.  If BLOCK
+;;; is already in a loop or is not dominated by the LOOP-HEAD, then we
+;;; return.  Otherwise, we add the block to the BLOCKS for LOOP and
+;;; recurse on its successors.
+(defun find-blocks-from-here (block loop)
+  (when (and (not (block-loop block))
+	     (dominates-p (loop-head loop) block))
+    (setf (block-loop block) loop)
+    (shiftf (block-loop-next block) (loop-blocks loop) block)
+    (dolist (succ (block-succ block))
+      (find-blocks-from-here succ loop))))
+
+
+;;; NOTE-LOOP-HEAD  --  Internal
+;;;
+;;; Create a loop structure to describe the loop headed by the block
+;;; HEAD.  If there is one already, just return.  If some retreating
+;;; edge into the head is from a block which isn't dominated by the
+;;; head, then we have the head of a strange loop segment.  We return
+;;; true if HEAD is part of a newly discovered strange loop.
+(defun note-loop-head (head component)
+  (let ((superior (find-superior head (component-outer-loop component))))
+    (unless (eq (loop-head superior) head)
+      (let ((result (make-loop :head head
+			       :kind :natural
+			       :superior superior
+			       :depth (1+ (loop-depth superior))))
+	    (number (block-number head)))
+	(push result (loop-inferiors superior))
+	(dolist (pred (block-pred head))
+	  (when (<= (block-number pred) number)
+	    (if (dominates-p head pred)
+		(push pred (loop-tail result))
+		(setf (loop-kind result) :strange))))
+	(eq (loop-kind result) :strange)))))
+
+
+;;; FIND-SUPERIOR  --  Internal
+;;;
+;;; Find the loop which would be the superior of a loop headed by
+;;; HEAD.  If there is already a loop with that head, then return that
+;;; loop.
+(defun find-superior (head loop)
+  (if (eq (loop-head loop) head)
+      loop
+      (dolist (inferior (loop-inferiors loop) loop)
+	(when (dominates-p (loop-head inferior) head)
+	  (return (find-superior head inferior))))))
+
+
+;;; FIND-STRANGE-LOOP-BLOCKS  --  Internal
+;;;
+;;; Do a graph walk to find the blocks in the strange loop which HEAD
+;;; is in.  BLOCK is the block we are currently at and COMPONENT is
+;;; the component we are in.  We do a walk forward from block, using
+;;; only edges which are not back edges.  We return true if there is a
+;;; path from BLOCK to HEAD, false otherwise.  If the BLOCK-FLAG is
+;;; true then we return.  We use two non-null values of FLAG to
+;;; indicate whether a path from the BLOCK back to HEAD was found.
+(defun find-strange-loop-blocks (block head)
+  (let ((flag (block-flag block)))
+    (cond (flag
+	   (if (eq flag :good)
+	       t
+	       nil))
+	  (t
+	   (setf (block-flag block) :bad)
+	   (unless (dominates-p block head)
+	     (dolist (succ (block-succ block))
+	       (when (find-strange-loop-blocks succ head)
+		 (setf (block-flag block) :good))))
+	   (eq (block-flag block) :good)))))
+
+;;; FIND-STRANGE-LOOP-SEGMENTS  --  Internal
+;;;
+;;; Do a graph walk to find the segments in the strange loop that has
+;;; BLOCK in it.  We walk forward, looking only at blocks in the loop
+;;; (flagged as :GOOD.)  Each block in the loop that has predecessors
+;;; outside of the loop is the head of a segment.  We enter the LOOP
+;;; structures in COMPONENT.
+(defun find-strange-loop-segments (block component)
+  (when (eq (block-flag block) :good)
+    (setf (block-flag block) :done)
+    (unless (every #'(lambda (x) (member (block-flag x) '(:good :done)))
+		   (block-pred block))
+      (note-loop-head block component))
+    (dolist (succ (block-succ block))
+      (find-strange-loop-segments succ component))))