This is the mail archive of the gcc-patches@gcc.gnu.org mailing list for the GCC project.


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]
Other format: [Raw text]

Re: [PATCH PR80153]Always generate folded type conversion in tree-affine


On Thu, Mar 30, 2017 at 2:03 PM, Bin.Cheng <amker.cheng@gmail.com> wrote:
> On Thu, Mar 30, 2017 at 11:37 AM, Richard Biener
> <richard.guenther@gmail.com> wrote:
>> On Wed, Mar 29, 2017 at 5:22 PM, Bin.Cheng <amker.cheng@gmail.com> wrote:
>>> On Tue, Mar 28, 2017 at 1:34 PM, Richard Biener
>>> <richard.guenther@gmail.com> wrote:
>>>> On Tue, Mar 28, 2017 at 2:01 PM, Bin Cheng <Bin.Cheng@arm.com> wrote:
>>>>> Hi,
>>>>> This patch is to fix PR80153.  As analyzed in the PR, root cause is tree_affine lacks
>>>>> ability differentiating (unsigned)(ptr + offset) and (unsigned)ptr + (unsigned)offset,
>>>>> even worse, it always returns the former expression in aff_combination_tree, which
>>>>> is wrong if the original expression has the latter form.  The patch resolves the issue
>>>>> by always returning the latter form expression, i.e, always trying to generate folded
>>>>> expression.  Also as analyzed in comment, I think this change won't result in substantial
>>>>> code gen difference.
>>>>> I also need to adjust get_computation_aff for test case gcc.dg/tree-ssa/reassoc-19.c.
>>>>> Well, I think the changed behavior is correct, but for case the original pointer candidate
>>>>> is chosen, it should be unnecessary to compute in uutype.  Also this adjustment only
>>>>> generates (unsigned)(pointer + offset) which is generated by tree-affine.c.
>>>>> Bootstrap and test on x86_64 and AArch64.  Is it OK?
>>>>
>>> Thanks for reviewing.
>>>> Hmm.  What is the desired goal?  To have all elts added have
>>>> comb->type as type?  Then
>>>> the type passed to add_elt_to_tree is redundant with comb->type.  It
>>>> looks like it
>>>> is always passed comb->type now.
>>> Yes, except pointer type comb->type, elts are converted to comb->type
>>> with this patch.
>>> The redundant type is removed in updated patch.
>>>
>>>>
>>>> ISTR from past work in this area that it was important for pointer
>>>> combinations to allow
>>>> both pointer and sizetype elts at least.
>>> Yes, It's still important to allow different types for pointer and
>>> offset in pointer type comb.
>>> I missed a pointer type check condition in the patch, fixed in updated patch.
>>>>
>>>> Your change is incomplete I think, for the scale == -1 and POINTER_TYPE_P case
>>>> elt is sizetype now, not of pointer type.  As said above, we are
>>>> trying to maintain
>>>> both pointer and sizetype elts with like:
>>>>
>>>>   if (scale == 1)
>>>>     {
>>>>       if (!expr)
>>>>         {
>>>>           if (POINTER_TYPE_P (TREE_TYPE (elt)))
>>>>             return elt;
>>>>           else
>>>>             return fold_convert (type1, elt);
>>>>         }
>>>>
>>>> where your earilier fold to type would result in not all cases handled the same
>>>> (depending whether scale was -1 for example).
>>> IIUC, it doesn't matter.  For comb->type being pointer type, the
>>> behavior remains the same.
>>> For comb->type being unsigned T, this elt is converted to ptr_offtype,
>>> rather than unsigned T,
>>> this doesn't matter because ptr_offtype and unsigned T are equal to
>>> each other, otherwise
>>> tree_to_aff_combination shouldn't distribute it as a single elt.
>>> Anyway, this is addressed in updated patch by checking pointer
>>> comb->type additionally.
>>> BTW, I think "scale==-1" case is a simple heuristic differentiating
>>> pointer_base and offset.
>>>
>>>>
>>>> Thus - shouldn't we simply drop the type argument (or rather the comb one?
>>>> that wide_int_ext_for_comb looks weird given we get a widest_int as input
>>>> and all the other wide_int_ext_for_comb calls around).
>>>>
>>>> And unconditionally convert to type, simplifying the rest of the code?
>>> As said, for pointer type comb, we need to keep current behavior; for
>>> other cases,
>>> unconditionally convert to comb->type is the goal.
>>>
>>> Bootstrap and test on x86_64 and AArch64.  Is this version OK?
>>
>> @@ -399,22 +400,20 @@ add_elt_to_tree (tree expr, tree type, tree elt,
>> const widest_int &scale_in,
>>           if (POINTER_TYPE_P (TREE_TYPE (elt)))
>>             return elt;
>>           else
>> -           return fold_convert (type1, elt);
>> +           return fold_convert (type, elt);
>>         }
>>
>> the conversion should already have been done.  For non-pointer comb->type
>> it has been converted to type by your patch.  For pointer-type comb->type
>> it should be either pointer type or ptrofftype ('type') already as well.
>>
>> That said, can we do sth like
>>
>> @@ -384,6 +395,12 @@ add_elt_to_tree (tree expr, tree type, t
>>
>>    widest_int scale = wide_int_ext_for_comb (scale_in, comb);
>>
>> +  if (! POINTER_TYPE_P (comb->type))
>> +    elt = fold_convert (comb->type, elt);
>> +  else
>> +    gcc_assert (POINTER_TYPE_P (TREE_TYPE (elt))
>> +               || types_compatible_p (TREE_TYPE (elt), type1));
> Hmm, this assert can be broken since we do STRIP_NOPS converting to
> aff_tree. It's not compatible for signed and unsigned integer types.
> Also, with this patch, we can even support elt of short type in a
> unsigned long comb, though this is useless.
>
>> +
>>    if (scale == -1
>>        && POINTER_TYPE_P (TREE_TYPE (elt)))
>>      {
>>
>> that is clearly do the conversion at the start in a way the state
>> of elt is more clear?
> Yes, thanks.  V3 patch attached (with gcc_assert removed).  Is it ok
> after bootstrap/test?

-      return fold_build2 (PLUS_EXPR, type1,
-                         expr, fold_convert (type1, elt));
+      return fold_build2 (PLUS_EXPR, type, expr, fold_convert (type, elt));

folding not needed(?)

-       return fold_build1 (NEGATE_EXPR, type1,
-                           fold_convert (type1, elt));
+       return fold_build1 (NEGATE_EXPR, type, fold_convert (type, elt));

likewise.

-      return fold_build2 (MINUS_EXPR, type1,
-                         expr, fold_convert (type1, elt));
+      return fold_build2 (MINUS_EXPR, type, expr, fold_convert (type, elt));

likewise.

Ok with removing those and re-testing.

Thanks,
Richard.

> Thanks,
> bin
>>
>> Richard.
>>
>>
>>
>>> Thanks,
>>> bin
>>>
>>> 2017-03-28  Bin Cheng  <bin.cheng@arm.com>
>>>
>>>     PR tree-optimization/80153
>>>     * tree-affine.c (add_elt_to_tree): Remove parameter TYPE.  Use type
>>>     of parameter COMB.  Convert elt to type of COMB it COMB is not of
>>>     pointer type.
>>>     (aff_combination_to_tree): Update calls to add_elt_to_tree.
>>>     * tree-ssa-loop-ivopts.c (alloc_iv): Pass in consistent types.
>>>     (get_computation_aff): Use utype directly for original candidate.
>>>
>>> gcc/testsuite/ChangeLog
>>> 2017-03-28  Bin Cheng  <bin.cheng@arm.com>
>>>
>>>     PR tree-optimization/80153
>>>     * gcc.c-torture/execute/pr80153.c: New.


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]