Re: [PATCH] Fix PR rtl-optimization/33796: valgrind error with -O2 for linux kernel code

[Kenneth Zadeck <zadeck at naturalbridge dot com>]

Peter Bergner wrote:
> I'm testing the following patch from Janis along with a comment about
> why we're changing from xmalloc to xcalloc.  Ok for mainline if it
> passes bootstrap and regression testing?
>
> Peter
>
> 	PR rtl-optimization/33796
> 	* sparseset.c (sparseset_alloc): Use xcalloc rather than xmalloc.
>
> Index: sparseset.c
> ===================================================================
> --- sparseset.c	(revision 131578)
> +++ sparseset.c	(working copy)
> @@ -30,7 +30,12 @@
>    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;
>   
approved,
thanks

kenny