[Bug target/71106] MIPS: Unaligned load/store instructions are not used to access a variable with an aligned attribute

["rguenth at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71106

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Target|                            |mips
                 CC|                            |ebotcazou at gcc dot gnu.org

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
I think that is "expected" behavior for strict-aling targets that do not
provide
a movmisalign handler.  But newer GCC (like GCC 6 you used) should behave
correctly here.  The issue seems to be that the misalign handling is restricted
to indirect references in expand_assignment.

Thus

Index: gcc/expr.c
===================================================================
--- gcc/expr.c  (revision 236309)
+++ gcc/expr.c  (working copy)
@@ -4654,9 +4654,7 @@ expand_assignment (tree to, tree from, b

   /* Handle misaligned stores.  */
   mode = TYPE_MODE (TREE_TYPE (to));
-  if ((TREE_CODE (to) == MEM_REF
-       || TREE_CODE (to) == TARGET_MEM_REF)
-      && mode != BLKmode
+  if (mode != BLKmode
       && !mem_ref_refers_to_non_mem_p (to)
       && ((align = get_object_alignment (to))
          < GET_MODE_ALIGNMENT (mode))

would fix that.  Without pruning some of the "pessimistic" handling in
get_object_alignment this will likely result in some code-gen regressions
though.

Index: gcc/builtins.c
===================================================================
--- gcc/builtins.c      (revision 236309)
+++ gcc/builtins.c      (working copy)
@@ -339,7 +339,7 @@ get_object_alignment_2 (tree exp, unsign
         Do so only if get_pointer_alignment_1 did not reveal absolute
         alignment knowledge and if using that alignment would
         improve the situation.  */
-      if (!addr_p && !known_alignment
+      if (!addr_p
          && TYPE_ALIGN (TREE_TYPE (exp)) > align)
        align = TYPE_ALIGN (TREE_TYPE (exp));
       else