--- /home/jfw/build/Scheme/chicken-core/runtime.c	2011-10-14 18:24:28.000000000 +0200
+++ runtime.c	2011-10-21 14:38:42.269533964 +0200
@@ -1790,10 +1790,20 @@
   return C_restore;
 }
 
+C_inline C_regparm int C_i_in_stackp(C_word x)
+{
+  C_word *ptr = (C_word *)(C_uword)x;
+
+#if C_STACK_GROWS_DOWNWARD
+  return ptr >= C_stack_pointer_test && ptr <= stack_bottom;
+#else
+  return ptr < C_stack_pointer_test && ptr >= stack_bottom;
+#endif
+}
 
 void C_fcall C_callback_adjust_stack(C_word *a, int size)
 {
-  if(!chicken_is_running && !C_in_stackp((C_word)a)) {
+  if(!chicken_is_running && !C_i_in_stackp((C_word)a)) {
     if(debug_mode)
       C_dbg(C_text("debug"), 
 	    C_text("callback invoked in lower stack region - adjusting limits:\n"
@@ -1968,7 +1978,7 @@
   key = hash_string(len, str, stable->size);
 
   if(C_truep(s = lookup(key, len, str, stable))) {
-    if(C_in_stackp(s)) C_mutate(slot, s);
+    if(C_i_in_stackp(s)) C_mutate(slot, s);
     
     return s;
   }
@@ -2109,19 +2119,11 @@
   return sym;
 }
 
-
 C_regparm int C_in_stackp(C_word x)
 {
-  C_word *ptr = (C_word *)(C_uword)x;
-
-#if C_STACK_GROWS_DOWNWARD
-  return ptr >= C_stack_pointer_test && ptr <= stack_bottom;
-#else
-  return ptr < C_stack_pointer_test && ptr >= stack_bottom;
-#endif
+  return C_i_in_stackp(x);
 }
 
-
 C_regparm int C_fcall C_in_heapp(C_word x)
 {
   C_byte *ptr = (C_byte *)(C_uword)x;
@@ -2569,7 +2571,7 @@
   while(n--) {
     x = va_arg(v, C_word);
 
-    if(C_in_stackp(x)) C_mutate(p++, x);
+    if(C_i_in_stackp(x)) C_mutate(p++, x);
     else *(p++) = x;
   }
 
@@ -2593,7 +2595,7 @@
   while(n--) {
     x = va_arg(v, C_word);
 
-    if(C_in_stackp(x)) C_mutate(p++, x);
+    if(C_i_in_stackp(x)) C_mutate(p++, x);
     else *(p++) = x;
   }
 
@@ -2670,7 +2672,7 @@
   C_uword count, bytes;
   C_word *p, **msp, bucket, last, item, container;
   C_header h;
-  C_byte *tmp, *start;
+  C_byte *tmp, *start = C_fromspace_top;
   LF_LIST *lfn;
   C_SCHEME_BLOCK *bp;
   C_GC_ROOT *gcrp;
@@ -2696,7 +2698,7 @@
   gc_mode = GC_MINOR;
 
   /* Entry point for second-level GC (on explicit request or because of full fromspace): */
-  if(C_setjmp(gc_restart) || (start = C_fromspace_top) >= C_fromspace_limit) {
+  if(C_setjmp(gc_restart) || start >= C_fromspace_limit) {
     if(gc_bell) {
       C_putchar(7);
       C_fflush(stdout);
@@ -3424,7 +3426,7 @@
         if(is_fptr(h))		/* forwarded? update l-table entry */
           loc = locative_table[ i ] = fptr_to_ptr(h);
         /* otherwise it must have been GC'd (since this is a minor one) */
-        else if(C_in_stackp(loc)) {
+        else if(C_i_in_stackp(loc)) {
           locative_table[ i ] = C_SCHEME_UNDEFINED;
           C_set_block_item(loc, 0, 0);
 	  ++invalidated;
@@ -3441,7 +3443,7 @@
           C_set_block_item(loc, 0, (C_uword)fptr_to_ptr(h) + offset);
 	  hi = i + 1;
 	}
-        else if(C_in_stackp(obj)) { /* pointed-at object GC'd, locative is invalid */
+        else if(C_i_in_stackp(obj)) { /* pointed-at object GC'd, locative is invalid */
           locative_table[ i ] = C_SCHEME_UNDEFINED;
           C_set_block_item(loc, 0, 0);
         }
@@ -5025,7 +5027,8 @@
   if(C_immediatep(x) || C_block_header(x) != C_PAIR_TAG)
     barf(C_BAD_ARGUMENT_TYPE_ERROR, "set-car!", x);
 
-  C_mutate(&C_u_i_car(x), val);
+  if(!C_immediatep(val) && C_i_in_stackp(val)) C_mutate(&C_u_i_car(x), val);
+  else C_u_i_car(x) = val;
   return C_SCHEME_UNDEFINED;
 }
 
@@ -5035,7 +5038,8 @@
   if(C_immediatep(x) || C_block_header(x) != C_PAIR_TAG)
     barf(C_BAD_ARGUMENT_TYPE_ERROR, "set-cdr!", x);
 
-  C_mutate(&C_u_i_cdr(x), val);
+  if(!C_immediatep(val) && C_i_in_stackp(val)) C_mutate(&C_u_i_cdr(x), val);
+  else C_u_i_cdr(x) = val;
   return C_SCHEME_UNDEFINED;
 }
 
@@ -5052,7 +5056,8 @@
 
     if(j < 0 || j >= C_header_size(v)) barf(C_OUT_OF_RANGE_ERROR, "vector-set!", v, i);
 
-    C_mutate(&C_block_item(v, j), x);
+    if(!C_immediatep(x) && C_i_in_stackp(x))  C_mutate(&C_block_item(v, j), x);
+    else C_block_item(v, j) = x;
   }
   else barf(C_BAD_ARGUMENT_TYPE_ERROR, "vector-set!", i);
 
@@ -6970,6 +6975,8 @@
   if(c == 3) {
     arg = va_arg(v, C_word);
     f = C_truep(arg);
+    if((arg & C_FIXNUM_BIT) != 0) size = C_unfix(arg);
+    else if(arg == C_SCHEME_END_OF_LIST) size = percentage(heap_size, C_heap_growth);
   }
   else if(c != 2) C_bad_min_argc(c, 2);
   else f = 1;
@@ -6977,11 +6984,6 @@
   C_save(k);
   va_end(v);
 
-  if(c == 3) {
-    if((arg & C_FIXNUM_BIT) != 0) size = C_unfix(arg);
-    else if(arg == C_SCHEME_END_OF_LIST) size = percentage(heap_size, C_heap_growth);
-  }
-
   if(size && !C_heap_size_is_fixed) {
     C_rereclaim2(size, 0);
     gc_2(NULL);
@@ -8073,10 +8075,10 @@
   flist->next = finalizer_list;
   finalizer_list = flist;
 
-  if(C_in_stackp(x)) C_mutate(&flist->item, x);
+  if(C_i_in_stackp(x)) C_mutate(&flist->item, x);
   else flist->item = x;
 
-  if(C_in_stackp(proc)) C_mutate(&flist->finalizer, proc);
+  if(C_i_in_stackp(proc)) C_mutate(&flist->finalizer, proc);
   else flist->finalizer = proc;
 
   ++live_finalizer_count;