an experiment: clearing the C stack in gc tests

* test-suite/lib.scm (clear-stale-stack-references): New helper.
* test-suite/tests/gc.test:
* test-suite/tests/threads.test: Use the new helper.

I removed the "unresolved" throw, as I'd like to see what the bots do
with this.

test-suite/lib.scm

@@ -1,6 +1,6 @@
 ;;;; test-suite/lib.scm --- generic support for testing
 ;;;; Copyright (C) 1999, 2000, 2001, 2004, 2006, 2007, 2009, 2010,
-;;;;   2011 Free Software Foundation, Inc.
+;;;;   2011, 2012 Free Software Foundation, Inc.
 ;;;;
 ;;;; This program is free software; you can redistribute it and/or
 ;;;; modify it under the terms of the GNU Lesser General Public
@@ -56,6 +56,9 @@
  ;; Using the debugging evaluator.
  with-debugging-evaluator with-debugging-evaluator*
 
+ ;; Clearing stale references on the C stack for GC-sensitive tests.
+ clear-stale-stack-references
+
  ;; Using a given locale
  with-locale with-locale* with-latin1-locale with-latin1-locale*
 
@@ -484,6 +487,17 @@
 (define-macro (with-debugging-evaluator . body)
   `(with-debugging-evaluator* (lambda () ,@body)))
 
+;; Recurse through a C function that should clear any values that might
+;; have spilled on the stack temporarily.  (The salient feature of
+;; with-continuation-barrier is that currently it is implemented as a C
+;; function that recursively calls the VM.)
+;;
+(define* (clear-stale-stack-references #:optional (n 10))
+  (if (positive? n)
+      (with-continuation-barrier
+       (lambda ()
+         (clear-stale-stack-references (1- n))))))
+
 ;;; Call THUNK with a given locale
 (define (with-locale* nloc thunk)
   (let ((loc #f))

test-suite/tests/gc.test

@@ -49,13 +49,6 @@
 ;;; 
 ;;;
 
-(define (stack-cleanup depth)
-  ;; Clean up stack space for DEPTH words.  This is defined here so that
-  ;; `peval' doesn't inline it.
-  (let cleanup ((i depth))
-    (and (> i 0)
-         (begin (cleanup (1- i)) i))))
-
 (with-test-prefix "gc"
 
   (pass-if "after-gc-hook gets called"
@@ -73,7 +66,7 @@
       (for-each (lambda (x) (guard (make-module))) (iota total))
 
       ;; Avoid false references to the modules on the stack.
-      (stack-cleanup 20)
+      (clear-stale-stack-references)
 
       (gc)
       (gc)   ;; twice: have to kill the weak vectors.
@@ -92,21 +85,9 @@
                  (define guardian (make-guardian))
                  (let ((f (list 'foo)))
                    (guardian f))
-                 ;; See below.
-                 ;; ((lambda () #t))
+                 ((@ (test-suite lib) clear-stale-stack-references))
                  (gc)(gc)(gc)
                  (guardian))
               ;; Prevent the optimizer from propagating f.
               #:opts '(#:partial-eval? #f))))
-      (if (not l)
-          ;; We think that something on the C stack in the VM is holding
-          ;; on to a reference to the list.  This happens on
-          ;; register-poor architectures, where more locals are spilled
-          ;; to the stack.  If more code runs before the (gc) is run,
-          ;; like a ((lambda () #t)), then the test passes.  So given
-          ;; that at some point, the reference will be dropped, we will
-          ;; count these cases as "unresolved" instead of "fail".
-          ;;
-          ;; See http://debbugs.gnu.org/cgi/bugreport.cgi?bug=10336.
-          (throw 'unresolved)
-          (equal? l '(foo))))))
+      (equal? l '(foo)))))

test-suite/tests/threads.test

@@ -1,6 +1,6 @@
 ;;;; threads.test --- Tests for Guile threading.    -*- scheme -*-
 ;;;;
-;;;; Copyright 2003, 2006, 2007, 2009, 2010, 2011 Free Software Foundation, Inc.
+;;;; Copyright 2003, 2006, 2007, 2009, 2010, 2011, 2012 Free Software Foundation, Inc.
 ;;;;
 ;;;; This library is free software; you can redistribute it and/or
 ;;;; modify it under the terms of the GNU Lesser General Public
@@ -36,13 +36,6 @@
     (equal? '(a b c) '(a b c))
     a))
 
-(define (stack-cleanup depth)
-  ;; Clean up stack space for DEPTH words.  This is defined here so that
-  ;; `peval' doesn't inline it.
-  (let cleanup ((i depth))
-    (and (> i 0)
-         (begin (cleanup (1- i)) i))))
-
 (if (provided? 'threads)
     (begin
 
@@ -410,7 +403,7 @@
             (g (let ((m (make-mutex))) (lock-mutex m) m))
 
             ;; Avoid false references to M on the stack.
-            (stack-cleanup 20)
+            (clear-stale-stack-references)
 
             (gc) (gc)
             (let ((m (g)))