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[PATCH] Fix PR rtl-optimization/33796: valgrind error with -O2 for linux kernel code
- From: Peter Bergner <bergner at vnet dot ibm dot com>
- To: gcc-patches at gcc dot gnu dot org
- Cc: Kenneth Zadeck <zadeck at naturalbridge dot com>, Janis Johnson <janis187 at us dot ibm dot com>
- Date: Wed, 16 Jan 2008 16:55:55 -0600
- Subject: [PATCH] Fix PR rtl-optimization/33796: valgrind error with -O2 for linux kernel code
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;