Hi!
Packed attribute/pragma isn't the only way to cause types
to be less than naturally aligned. Aligned attribute can do the same thing
(and, for non-aggregates, packed attribute is ignored and thus aligned(X)
is the only way to express it).
The alignment_reachable targhook takes (or should take) care of other
reasons why peeling the loop doesn't always lead into naturally aligned
vectors (e.g. when for the types ADJUST_FIELD_ALIGN sometimes lowers
alignment and thus pointers to the fields aren't naturally aligned,
eventhough TYPE_ALIGN says it should).
Bootstrapped/regtested on x86_64-linux and i686-linux, approved by richi
in bugzilla/on IRC, committed to trunk/4.6.
2011-04-08 Jakub Jelinek <ja...@redhat.com>
PR tree-optimization/48377
* tree-vect-data-refs.c (vector_alignment_reachable_p): Set
is_packed to true even for types with smaller TYPE_ALIGN than
TYPE_SIZE.
* gcc.dg/vect/pr48377.c: New test.
--- gcc/tree-vect-data-refs.c.jj 2011-03-18 09:43:50.000000000 +0100
+++ gcc/tree-vect-data-refs.c 2011-04-08 11:05:22.305451288 +0200
@@ -1143,6 +1143,9 @@ vector_alignment_reachable_p (struct dat
if (ba)
is_packed = contains_packed_reference (ba);
+ if (compare_tree_int (TYPE_SIZE (type), TYPE_ALIGN (type)) > 0)
+ is_packed = true;
+
if (vect_print_dump_info (REPORT_DETAILS))
fprintf (vect_dump, "Unknown misalignment, is_packed = %d",is_packed);
if (targetm.vectorize.vector_alignment_reachable (type, is_packed))
--- gcc/testsuite/gcc.dg/vect/pr48377.c.jj 2011-04-08 10:55:31.317420241
+0200
+++ gcc/testsuite/gcc.dg/vect/pr48377.c 2011-04-08 10:59:31.203402115 +0200
@@ -0,0 +1,25 @@
+/* PR tree-optimization/48377 */
+/* { dg-do run } */
+
+typedef unsigned int U __attribute__((__aligned__ (1), __may_alias__));
+
+__attribute__((noinline, noclone)) unsigned int
+foo (const char *s, int len)
+{
+ const U *p = (const U *) s;
+ unsigned int f = len / sizeof (unsigned int), hash = len, i;
+
+ for (i = 0; i < f; ++i)
+ hash += *p++;
+ return hash;
+}
+
+char buf[64] __attribute__((aligned (32)));
+
+int
+main (void)
+{
+ return foo (buf + 1, 26) != 26;
+}
+
+/* { dg-final { cleanup-tree-dump "vect" } } */
Jakub
