Re: [PATCH]Fix computation of offset in ivopt

["Bin.Cheng" <amker dot cheng at gmail dot com>]

On Wed, Nov 13, 2013 at 7:26 PM, Richard Biener
<richard.guenther@gmail.com> wrote:
> On Wed, Nov 13, 2013 at 12:18 PM, Bin.Cheng <amker.cheng@gmail.com> wrote:
>> On Thu, Nov 7, 2013 at 6:47 PM, Richard Biener
>> <richard.guenther@gmail.com> wrote:
>>> On Wed, Nov 6, 2013 at 6:06 PM, Richard Sandiford
>>> <rdsandiford@googlemail.com> wrote:
>>>> Hi,
>>>>
>>>> "bin.cheng" <bin.cheng@arm.com> writes:
>>>>> Index: gcc/tree-ssa-loop-ivopts.c
>>>>> ===================================================================
>>>>> --- gcc/tree-ssa-loop-ivopts.c        (revision 203267)
>>>>> +++ gcc/tree-ssa-loop-ivopts.c        (working copy)
>>>>> @@ -2037,12 +2037,12 @@ find_interesting_uses (struct ivopts_data *data)
>>>>>
>>>>>  static tree
>>>>>  strip_offset_1 (tree expr, bool inside_addr, bool top_compref,
>>>>> -             unsigned HOST_WIDE_INT *offset)
>>>>> +             HOST_WIDE_INT *offset)
>>>>>  {
>>>>>    tree op0 = NULL_TREE, op1 = NULL_TREE, tmp, step;
>>>>>    enum tree_code code;
>>>>>    tree type, orig_type = TREE_TYPE (expr);
>>>>> -  unsigned HOST_WIDE_INT off0, off1, st;
>>>>> +  HOST_WIDE_INT off0, off1, st;
>>>>>    tree orig_expr = expr;
>>>>>
>>>>>    STRIP_NOPS (expr);
>>>>> @@ -2133,19 +2133,32 @@ strip_offset_1 (tree expr, bool inside_addr, bool
>>>>>        break;
>>>>>
>>>>>      case COMPONENT_REF:
>>>>> -      if (!inside_addr)
>>>>> -     return orig_expr;
>>>>> +      {
>>>>> +     tree field;
>>>>>
>>>>> -      tmp = component_ref_field_offset (expr);
>>>>> -      if (top_compref
>>>>> -       && cst_and_fits_in_hwi (tmp))
>>>>> -     {
>>>>> -       /* Strip the component reference completely.  */
>>>>> -       op0 = TREE_OPERAND (expr, 0);
>>>>> -       op0 = strip_offset_1 (op0, inside_addr, top_compref, &off0);
>>>>> -       *offset = off0 + int_cst_value (tmp);
>>>>> -       return op0;
>>>>> -     }
>>>>> +     if (!inside_addr)
>>>>> +       return orig_expr;
>>>>> +
>>>>> +     tmp = component_ref_field_offset (expr);
>>>>> +     field = TREE_OPERAND (expr, 1);
>>>>> +     if (top_compref
>>>>> +         && cst_and_fits_in_hwi (tmp)
>>>>> +         && cst_and_fits_in_hwi (DECL_FIELD_BIT_OFFSET (field)))
>>>>
>>>> While comparing output for wide-int and mainline, I noticed that
>>>> this condition is now always false on x86_64, since DECL_FIELD_BIT_OFFSET
>>>> is a 128-bit bitsizetype and since cst_and_fits_in_hwi rejects constants
>>>> with precision greater than HWI:
>>>>
>>>>   if (TREE_CODE (x) != INTEGER_CST)
>>>>     return false;
>>>>
>>>>   if (TYPE_PRECISION (TREE_TYPE (x)) > HOST_BITS_PER_WIDE_INT)
>>>>     return false;
>>>
>>> I think that's simply overly restrictive on the side of cst_and_fits_in_hwi.
>>> I suppose this function is meant to complement int_cst_value (digging
>>> in history might be nice here).
>>>
>>>> Should this be host_integerp (DECL_FIELD_BIT_OFFSET (field), 0) instead?
>>>
>>> That's not the same as it rejects -1U.  The function seems to ask
>>> if the value, if casted to unsigned fits in a HOST_WIDE_INT.
>>>
>>> So just drop the precision check from cst_and_fits_in_hwi.
>> Hi,
>> With check in of patch lowering address expression in ivo, that piece
>> of code won't be executed anymore.  So still need to drop precision
>> check in cst_and_fits_in_hwi?  The major part of strip_offset_1 can be
>> cleaned now.
>
> I think it's a good cleanup, so if you can bootstrap & test that
> change separately....?
Will do.

-- 
Best Regards.