re PR rtl-optimization/33796 (valgrind error with -O2 for linux kernel code)

	PR rtl-optimization/33796
	* sparseset.c (sparseset_alloc): Use xcalloc rather than xmalloc.

Co-Authored-By: Peter Bergner <bergner@vnet.ibm.com>

From-SVN: r131589

gcc/ChangeLog

+2007-01-16  Janis Johnson  <janis187@us.ibm.com>
+	    Peter Bergner  <bergner@vnet.ibm.com>
+
+	PR rtl-optimization/33796
+	* sparseset.c (sparseset_alloc): Use xcalloc rather than xmalloc.
+
 2008-01-16  John David Anglin  <dave.anglin@nrc-cnrc.gc.ca>
 
 	PR libgfortran/34699

gcc/sparseset.c

@@ -30,7 +30,12 @@ sparseset_alloc (SPARSESET_ELT_TYPE n_elms)
   unsigned int n_bytes = sizeof (struct sparseset_def)
 			 + ((n_elms - 1) * 2 * sizeof (SPARSESET_ELT_TYPE));
 
-  sparseset set = (sparseset) xmalloc (n_bytes);
+  /* We use xcalloc rather than xmalloc to silence some valgrind uninitialized
+     read errors when accessing set->sparse[n] when "n" is not, and never has
+     been, in the set.  These uninitialized reads are expected, by design and
+     harmless.  If this turns into a performance problem due to some future
+     additional users of sparseset, we can revisit this decision.  */
+  sparseset set = (sparseset) xcalloc (1, n_bytes);
   set->dense = &(set->elms[0]);
   set->sparse = &(set->elms[n_elms]);
   set->size = n_elms;