Follow-up improvements for last change in gmalloc.c.

 src/gmalloc.c (aligned_alloc): Don't allocate more memory than
 needed, and don't reallocate if the initial allocation already
 fits the bill.  Suggested by Ken Brown <kbrown@cornell.edu>.

Fixes: debbugs:16901

1 files changed, 28 insertions, 15 deletions

diff --git a/src/gmalloc.c b/src/gmalloc.c
index f8d0cfdc30a..9fd62407285 100644
--- a/src/gmalloc.c
+++ b/src/gmalloc.c
@@ -38,6 +38,10 @@ License along with this library.  If not, see <http://www.gnu.org/licenses/>.
 #include <w32heap.h>    /* for sbrk */
 #endif
 
+#ifdef emacs
+extern void emacs_abort (void);
+#endif
+
 #ifdef  __cplusplus
 extern "C"
 {
@@ -1594,24 +1598,33 @@ aligned_alloc (size_t alignment, size_t size)
   /* Figure out how much we will need to pad this particular block
      to achieve the required alignment.  */
   adj = (uintptr_t) result % alignment;
+  if (adj == 0)
+    adj = alignment;
 
-  do
+  if (adj != 1)
     {
-      /* Reallocate the block with only as much excess as it needs.  */
-      free (result);
-      result = malloc (size + alignment - adj);
-      if (result == NULL)       /* Impossible unless interrupted.  */
-        return NULL;
-
-      lastadj = adj;
-      adj = (uintptr_t) result % alignment;
-      /* It's conceivable we might have been so unlucky as to get a
-         different block with weaker alignment.  If so, this block is too
-         short to contain SIZE after alignment correction.  So we must
-         try again and get another block, slightly larger.  */
-    } while (adj < lastadj);
+      do
+        {
+          /* Reallocate the block with only as much excess as it
+             needs.  */
+          free (result);
+          result = malloc (size + alignment - adj);
+          if (result == NULL)   /* Impossible unless interrupted.  */
+            return NULL;
+
+          lastadj = adj;
+          adj = (uintptr_t) result % alignment;
+          if (adj == 0)
+            adj = alignment;
+          /* It's conceivable we might have been so unlucky as to get
+             a different block with weaker alignment.  If so, this
+             block is too short to contain SIZE after alignment
+             correction.  So we must try again and get another block,
+             slightly larger.  */
+        } while (adj < lastadj);
+    }
 
-  if (adj != 0)
+  if (adj != alignment)
     {
       /* Record this block in the list of aligned blocks, so that `free'
          can identify the pointer it is passed, which will be in the middle