From 9c2fc61fe8c2208bb46118df074358e8d9bc7f2a Mon Sep 17 00:00:00 2001
From: Douglas Katzman <dougk@google.com>
Date: Sat, 31 Oct 2015 19:25:54 -0400
Subject: [PATCH] Fix NTH-VALUE for huge constant N.

---
 NEWS                       |  3 +++
 src/code/macros.lisp       | 22 ++++++++++++----------
 tests/compiler-2.pure.lisp |  6 ++++++
 3 files changed, 21 insertions(+), 10 deletions(-)

diff --git a/NEWS b/NEWS
index 9d2480431..abae6ce3f 100644
--- a/NEWS
+++ b/NEWS
@@ -1,4 +1,7 @@
 ;;;; -*- coding: utf-8; fill-column: 78 -*-
+changes relative to sbcl-1.3.0:
+  * bug fix: NTH-VALUE does not cause stack overflow. (lp#1511419)
+
 changes in sbcl-1.3.0 relative to sbcl-1.2.16:
   * minor incompatible change: the environment passed to a macro/setf/deftype
     expander is not always an object of type SB-KERNEL:LEXENV.
diff --git a/src/code/macros.lisp b/src/code/macros.lisp
index a62fa3fab..5f9cda3af 100644
--- a/src/code/macros.lisp
+++ b/src/code/macros.lisp
@@ -480,7 +480,7 @@ invoked. In that case it will store into PLACE and start over."
 
 ;;;; miscellaneous macros
 
-(defmacro-mundanely nth-value (n form)
+(defmacro-mundanely nth-value (n form &environment env)
   #!+sb-doc
   "Evaluate FORM and return the Nth value (zero based)
  without consing a temporary list of values."
@@ -491,18 +491,20 @@ invoked. In that case it will store into PLACE and start over."
   ;; form will take longer than can be described as adequate, as the
   ;; optional dispatch mechanism for the M-V-B gets increasingly
   ;; hairy.
-  (if (integerp n)
-      (let ((dummy-list (make-gensym-list n))
-            (keeper (sb!xc:gensym "KEEPER")))
-        `(multiple-value-bind (,@dummy-list ,keeper) ,form
-           (declare (ignore ,@dummy-list))
-           ,keeper))
+  (let ((val (and (sb!xc:constantp n env) (constant-form-value n env))))
+    (if (and (integerp val) (<= 0 val 10)) ; Arbitrary limit.
+        (let ((dummy-list (make-gensym-list val))
+              (keeper (sb!xc:gensym "KEEPER")))
+          `(multiple-value-bind (,@dummy-list ,keeper) ,form
+             (declare (ignore ,@dummy-list))
+             ,keeper))
       ;; &MORE conversion handily deals with non-constant N,
       ;; avoiding the unstylish practice of inserting FORM into the
       ;; expansion more than once to pick off a few small values.
-      `(multiple-value-call
-           (lambda (n &rest list) (nth (truly-the index n) list))
-         (the index ,n) ,form)))
+      ;; This is not as good as above, because it uses TAIL-CALL-VARIABLE.
+        `(multiple-value-call
+             (lambda (n &rest list) (nth (truly-the index n) list))
+           (the index ,n) ,form))))
 
 (defmacro-mundanely declaim (&rest specs)
   #!+sb-doc
diff --git a/tests/compiler-2.pure.lisp b/tests/compiler-2.pure.lisp
index 9b0d38975..79d5d87ff 100644
--- a/tests/compiler-2.pure.lisp
+++ b/tests/compiler-2.pure.lisp
@@ -86,3 +86,9 @@
 (with-test (:name :make-array-nil-no-warning)
   (assert-no-signal
    (compile nil '(lambda () (make-array '(2 2) :element-type nil)))))
+
+(with-test (:name :nth-value-huge-n-works)
+  (flet ((return-a-ton-of-values ()
+           (values-list (loop for i below 5000 collect i))))
+    (assert (= (nth-value 1 (return-a-ton-of-values)) 1))
+    (assert (= (nth-value 4000 (return-a-ton-of-values)) 4000))))
-- 
2.11.4.GIT