Re: [PATCH v2, rtl-optimization]: Fix PR54457, [x32] Fail to combine 64bit index + constant

[Uros Bizjak <ubizjak at gmail dot com>]

On Thu, Sep 27, 2012 at 8:08 PM,  <Paul_Koning@dell.com> wrote:

>>>>>> I agree (subreg:M (op:N A C) 0) to (op:M (subreg:N (A 0)) C) is
>>>>>> a good transformation, but why do we need to handle as special
>>>>>> the case where the subreg is itself the operand of a plus or minus?
>>>>>> I think it should happen regardless of where the subreg occurs.
>>>>>
>>>>> Don't we need to restrict this to the low part though?
>>>>
>>>> ...
>>
>> After some off-line discussion with Richard, attached is v2 of the patch.
>>
>> 2012-09-27  Uros Bizjak  <ubizjak@gmail.com>
>>
>>        PR rtl-optimization/54457
>>        * simplify-rtx.c (simplify_subreg):
>>       Simplify (subreg:SI (op:DI ((x:DI) (y:DI)), 0)
>>       to (op:SI (subreg:SI (x:DI) 0) (subreg:SI (x:DI) 0)).
>> ...
>
> Is it just specific to DI -> SI, or is it for any large mode -> smaller mode, like SI -> HI?

Oh, I just copied v1 ChangeLog. The patch converts all modes where
size of mode M < size of mode N. Updated ChangeLog reads:

2012-09-27  Uros Bizjak  <ubizjak@gmail.com>

        PR rtl-optimization/54457
        * simplify-rtx.c (simplify_subreg):
	Simplify (subreg:M (op:N ((x:N) (y:N)), 0)
     	to (op:M (subreg:M (x:N) 0) (subreg:M (x:N) 0)), where
	the outer subreg is effectively a truncation to the original mode M.

testsuite/ChangeLog:

2012-09-27  Uros Bizjak  <ubizjak@gmail.com>

        PR rtl-optimization/54457
        * gcc.target/i386/pr54457.c: New test.

Uros.