[RFC/SCCVN] Handle BIT_INSERT_EXPR in vn_nary_op_eq

On Wed, Jul 19, 2017 at 11:13 AM, Richard Biener
<richard.guenther@gmail.com> wrote:
> On July 19, 2017 6:10:28 PM GMT+02:00, Andrew Pinski <pinskia@gmail.com> wrote:
>>On Mon, Jul 17, 2017 at 3:02 AM, Richard Biener
>><richard.guenther@gmail.com> wrote:
>>> On Thu, Jul 13, 2017 at 6:18 AM, Andrew Pinski <pinskia@gmail.com>
>>wrote:
>>>> On Wed, Jul 12, 2017 at 9:10 PM, Marc Glisse <marc.glisse@inria.fr>
>>wrote:
>>>>> On Wed, 12 Jul 2017, Andrew Pinski wrote:
>>>>>
>>>>>> Hi,
>>>>>>  Unlike most other expressions, BIT_INSERT_EXPR has an implicit
>>>>>> operand of the precision/size of the second operand.  This means
>>if we
>>>>>> have an integer constant for the second operand and that compares
>>to
>>>>>> the same constant value, vn_nary_op_eq would return that these two
>>>>>> expressions are the same.  But in the case I was looking into the
>>>>>> integer constants had different types, one with 1 bit precision
>>and
>>>>>> the other with 2 bit precision which means the BIT_INSERT_EXPR
>>were
>>>>>> not equal at all.
>>>>>>
>>>>>> This patches the problem by checking to see if BIT_INSERT_EXPR's
>>>>>> operand 1's (second operand) type  has different precision to
>>return
>>>>>> false.
>>>>>>
>>>>>> Is this the correct location or should we be checking for this
>>>>>> differently?  If this is the correct location, is the patch ok?
>>>>>> Bootstrapped and tested on aarch64-linux-gnu with no regressions
>>(and
>>>>>> also tested with a few extra patches to expose BIT_INSERT_EXPR).
>>>>>>
>>>>>> Thanks,
>>>>>> Andrew Pinski
>>>>>>
>>>>>> ChangeLog:
>>>>>> * tree-ssa-sccvn.c (vn_nary_op_eq): Check BIT_INSERT_EXPR's
>>operand 1
>>>>>> to see if the types precision matches.
>>>>>
>>>>>
>>>>> Hello,
>>>>>
>>>>> since BIT_INSERT_EXPR is implicitly an expression with 4 arguments,
>>it makes
>>>>> sense that we may need a few such special cases. But shouldn't the
>>hash
>>>>> function be in sync with the equality comparator? Does
>>operand_equal_p need
>>>>> the same?
>>>>
>>>> The hash function does not need to be exactly the same.  The only
>>>> requirement there is if vn_nary_op_eq returns true then the hash has
>>>> to be the same.  Now we could improve the hash by using the
>>precision
>>>> which will allow us not to compare as much in some cases.
>>>>
>>>> Yes operand_equal_p needs the same handling; I did not notice that
>>>> until you mention it..
>>>> Right now it does:
>>>>         case BIT_INSERT_EXPR:
>>>>           return OP_SAME (0) && OP_SAME (1) && OP_SAME (2);
>>>
>>> Aww.  The issue is that operand_equal_p treats INTEGER_CSTs of
>>different
>>> type/precision but the same value as equal.
>>>
>>> Revisiting that, while a good idea, shouldn't block a fix here.  So
>>...
>>>
>>> Index: tree-ssa-sccvn.c
>>> ===================================================================
>>> --- tree-ssa-sccvn.c    (revision 250159)
>>> +++ tree-ssa-sccvn.c    (working copy)
>>> @@ -2636,6 +2636,14 @@ vn_nary_op_eq (const_vn_nary_op_t const
>>>      if (!expressions_equal_p (vno1->op[i], vno2->op[i]))
>>>        return false;
>>>
>>> +  /* BIT_INSERT_EXPR has an implict operand as the type precision
>>> +     of op1.  Need to check to make sure they are the same.  */
>>> +  if (vno1->opcode == BIT_INSERT_EXPR)
>>> +    if (INTEGRAL_TYPE_P (TREE_TYPE (vno1->op[0]))
>>> +       && TYPE_PRECISION (TREE_TYPE (vno1->op[1]))
>>> +           != TYPE_PRECISION (TREE_TYPE (vno2->op[1])))
>>> +      return false;
>>> +
>>>
>>> the case can be restricted to INTEGER_CST vno1->op[0] I think:
>>>
>>>   if (vno1->opcode == BIT_INSERT_EXPR
>>>       && TREE_CODE (vno1->op[0]) == INTEGER_CST
>>>       && TYPE_PRECISION (....
>>>
>>> and yes, operand_equal_p needs a similar fix.  Can you re-post with
>>that added?
>>
>>Here is that with the changes you requested too.
>>
>>> Do you have a testcase?
>>
>>I don't have one which fails with the trunk.  With lowering of
>>bit-fields accesses (which I hope to submit soon; just getting in the
>>required patches first), many testcases fail (bootstrap fails for the
>>same reason too).
>>
>>OK? Bootstrapped and tested on aarch64-linux-gnu with no regressions.
>
> In the fold-const.c hunk you need to verify arg1 op0 is an INTEGER_CST.  This is not necessary in sccvn because we passed operand_equal_p first.
>
> OK with that change.

This is what I applied in the end. It is not op0 that needs to be
changed here but rather op1; I had a typo in the fold-const.c check.

Thanks,
Andrew

>
> Richard.
>
>>Thanks,
>>Andrew
>>
>>ChangeLog:
>>* tree-ssa-sccvn.c (vn_nary_op_eq): Check BIT_INSERT_EXPR's operand 1
>>to see if the types precision matches.
>>* fold-const.c (operand_equal_p): Likewise,
>>
>>
>>>
>>> Thanks,
>>> Richard.
>>>
>>>> Thanks,
>>>> Andrew Pinski
>>>>
>>>>>
>>>>> --
>>>>> Marc Glisse
>