2012-01-27 Richard Guenther <rguenther@suse.de>

	PR tree-optimization/50444
	* tree-sra.c (build_ref_for_offset): Properly adjust the
	MEM_REF type for unaligned accesses.

	* gcc.dg/torture/pr50444.c: New testcase.


git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@183630 138bc75d-0d04-0410-961f-82ee72b054a4

1 files changed, 19 insertions, 0 deletions

diff --git a/gcc/tree-sra.c b/gcc/tree-sra.c
index f4146b2acbc..fa67e94cca3 100644
--- a/gcc/tree-sra.c
+++ b/gcc/tree-sra.c
@@ -1461,6 +1461,8 @@ build_ref_for_offset (location_t loc, tree base, HOST_WIDE_INT offset,
   tree prev_base = base;
   tree off;
   HOST_WIDE_INT base_offset;
+  unsigned HOST_WIDE_INT misalign;
+  unsigned int align;
 
   gcc_checking_assert (offset % BITS_PER_UNIT == 0);
 
@@ -1506,6 +1508,23 @@ build_ref_for_offset (location_t loc, tree base, HOST_WIDE_INT offset,
       base = build_fold_addr_expr (unshare_expr (base));
     }
 
+  /* If prev_base were always an originally performed access
+     we can extract more optimistic alignment information
+     by looking at the access mode.  That would constrain the
+     alignment of base + base_offset which we would need to
+     adjust according to offset.
+     ???  But it is not at all clear that prev_base is an access
+     that was in the IL that way, so be conservative for now.  */
+  align = get_pointer_alignment_1 (base, &misalign);
+  misalign += (double_int_sext (tree_to_double_int (off),
+				TYPE_PRECISION (TREE_TYPE (off))).low
+	       * BITS_PER_UNIT);
+  misalign = misalign & (align - 1);
+  if (misalign != 0)
+    align = (misalign & -misalign);
+  if (align < TYPE_ALIGN (exp_type))
+    exp_type = build_aligned_type (exp_type, align);
+
   return fold_build2_loc (loc, MEM_REF, exp_type, base, off);
 }