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Subject: [Bug tree-optimization/50444] [4.6/4.7 Regression] -ftree-sra ignores alignment
Date: Mon, 16 Jan 2012 15:58:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50444

--- Comment #13 from Richard Guenther <rguenth at gcc dot gnu.org> 2012-01-16 15:41:50 UTC ---
Or, transfering the alignment:

Index: tree-sra.c
===================================================================
--- tree-sra.c  (revision 183205)
+++ tree-sra.c  (working copy)
@@ -2294,15 +2294,17 @@ propagate_subaccesses_across_link (struc
        {
          tree t = lacc->base;

-         lacc->type = racc->type;
-         if (build_user_friendly_ref_for_offset (&t, TREE_TYPE (t),
-                                                 lacc->offset, racc->type))
+         if (lacc->type == racc->type
+             && build_user_friendly_ref_for_offset (&t, TREE_TYPE (t),
+                                                    lacc->offset, lacc->type))
            lacc->expr = t;
          else
            {
-             lacc->expr = build_ref_for_model (EXPR_LOCATION (lacc->base),
-                                               lacc->base, lacc->offset,
-                                               racc, NULL, false);
+             lacc->type = build_aligned_type (racc->type,
+                                              get_object_alignment
(lacc->expr));
+             lacc->expr = build_ref_for_offset (EXPR_LOCATION (lacc->base),
+                                                lacc->base, lacc->offset,
+                                                lacc->type, NULL, false);
              lacc->grp_no_warning = true;
            }
        }

note the build_user_friendly_ref_for_offset which is really bogus as it
would construct component-refs out of thin air.  The above probably
completely disables that path ...

get_object_alignment is a little conservative - we can and need to
do better by mimicking what expand does.  Note that we can't use
build_ref_for_model here.

With the above the testcase passes as well and we still scalarize:

  SR.7_10 = SR.6_11;
  c1x128$m_2 = SR.7_10;
  c4x32_15 = c1x128$m_2;
  MEM[(struct  *)&D.1760] = c4x32_15;