On Thu, Sep 27, 2012 at 8:08 PM, <paul_kon...@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 <ubiz...@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 <ubiz...@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 <ubiz...@gmail.com>
PR rtl-optimization/54457
* gcc.target/i386/pr54457.c: New test.
Uros.
