[Bug bootstrap/61320] [4.10 regression] ICE in jcf-parse.c:1622 (parse_class_file

[ebotcazou at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61320

--- Comment #61 from Eric Botcazou <ebotcazou at gcc dot gnu.org> ---
> Ok, I suppose
> 
>         lduh    [%g3], %g4      ! MEM[base: ptr_110, offset: 0B], min_line
> 
> is not an instruction that works with unaligned %g3.

Right, every load must be aligned.

> ;; min_line_106 = (int) _215;
> 
> (insn 921 920 922 (set (reg:HI 482)
>         (mem:HI (reg/v/f:SI 185 [ ptr ]) [0 MEM[base: ptr_110, offset: 0B]+0
> S2 A8])) /vol/gcc/src/hg/trunk/local/gcc/java/jcf-parse.c:1622 -1
>      (nil))
> 
> a (mem:HI ...) with A8.  I wonder if we should ICE somewhere if such kind
> of MEM is in the RTL instruction stream on a STRICT_ALIGNMENT platform?

No, it's undefined behavior at run time only.

> Ah, so the issue is that may_be_unaligned does
> 
> 1706      unsigned int align = TYPE_ALIGN (TREE_TYPE (ref));
> 1707
> 1708      unsigned HOST_WIDE_INT bitpos;
> 1709      unsigned int ref_align;
> 1710      get_object_alignment_1 (ref, &ref_align, &bitpos);
> 1711      if (ref_align < align
> 1712          || (bitpos % align) != 0
> 1713          || (bitpos % BITS_PER_UNIT) != 0)
> 1714        return true;
> 
> thus it queries TYPE_ALIGN (TREE_TYPE (ref)) which is 8 - and _not_
> mode alignment which is what matters on STRICT_ALIGNMENT targets.

Yes, and that's what the original implementation actually did, see:
  https://gcc.gnu.org/ml/gcc-patches/2014-01/msg00717.html

> Fix:
> 
> Index: gcc/tree-ssa-loop-ivopts.c
> ===================================================================
> --- gcc/tree-ssa-loop-ivopts.c  (revision 213050)
> +++ gcc/tree-ssa-loop-ivopts.c  (working copy)
> @@ -1704,6 +1704,8 @@ may_be_unaligned_p (tree ref, tree step)
>      return false;
>  
>    unsigned int align = TYPE_ALIGN (TREE_TYPE (ref));
> +  if (GET_MODE_ALIGNMENT (TYPE_MODE (TREE_TYPE (ref))) > align)
> +    align = GET_MODE_ALIGNMENT (TYPE_MODE (TREE_TYPE (ref)));
>  
>    unsigned HOST_WIDE_INT bitpos;
>    unsigned int ref_align;
> 
> can you test and apply that patch?

I think that it needs to be applied on both mainline and 4.9 branch then.