[m-rev.] diff: Fixed a problem with gcc 3.3

[Paul Bone]

Fix compatibility with older versions of GCC.

runtime/mercury_memory_zones.c:
    GCC 3.3 reported a variable used uninitialised in this function.
    It simply couldn't infer that the variable would be initialised, so a
    dummy initialisation and explanation has been added.

Index: runtime/mercury_memory_zones.c
===================================================================
RCS file: /home/mercury/mercury1/repository/mercury/runtime/mercury_memory_zones.c,v
retrieving revision 1.46
diff -u -r1.46 mercury_memory_zones.c
--- runtime/mercury_memory_zones.c	4 Jan 2012 17:37:40 -0000	1.46
+++ runtime/mercury_memory_zones.c	22 May 2012 06:40:46 -0000
@@ -1214,9 +1214,19 @@
             */
             cur_list = free_memory_zones;
 
+            /*
+            ** GCC 3.3 thinks that oldest_lru_token will used uninitialised.
+            ** But it won't, lru_free_memory_zones will always be NULL and
+            ** therefore the ** if branch will be followed to set this
+            ** variable before it is read in the condition of the else if
+            ** branch.
+            **
+            ** To avoid this problem we initialise oldest_lru_token.
+            */
+            oldest_lru_token = 0;
             while(cur_list != NULL) {
                 cur_lru_token = cur_list->MR_zonesfree_minor_tail->MR_zone_lru_token;
-                if (!lru_free_memory_zones) {
+                if (lru_free_memory_zones == NULL) {
                     oldest_lru_token = cur_lru_token;
                     lru_free_memory_zones = cur_list;
                 } else if (cur_lru_token < oldest_lru_token) {
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