Re: Tree-SSA and POST_INC address mode inompatible in GCC4?

[Kenneth Zadeck <zadeck@naturalbridge.com>]

Zdenek Dvorak wrote:
> Hi,
>
>   
>> I believe that this is something new and is most likely fallout from
>> diego's reworking of the tree to rtl converter.
>>
>> To fix this will require a round of copy propagation, most likely in
>> concert with some induction variable detection, since the most
>> profitable place for this will be in loops.  
>>
>> I wonder if any of this effects the rtl level induction variable
>> discovery?
>>     
>
> it should not (iv analysis is able to deal with this kind of ivs).
>
> Zdenek
>
>   
does the iv analysis canonize them in a way that we should perhaps
consider moving the auto-inc detection after the iv analysis?
>>> Hi, Ramana,
>>> I tried the trunk version  with/without your patch. It still produces
>>> the same code as gcc4.2.2 does. In auto-inc-dec.c, the comments say 
>>>
>>>          *a
>>>            ...
>>>            a <- a + c
>>>
>>>         becomes
>>>
>>>            *(a += c) post
>>>
>>> But the problem is after Tree-SSA pass,  there is no
>>>            a <- a + c
>>> But something like
>>>            a_1 <- a + c
>>>
>>> Unless the auto-inc-dec.c can reverse a_1 <- a + c to a <- a + c. I
>>> don't see this transformation is applicable in most scenarios. Any
>>> comments? 
>>>
>>> Cheers,
>>> Bingfeng
>>>
>>>