A question about bytecodes + unsigned load performance ./. add performace

[Tom Rodriguez]

The client VM doesn't have any optimizations around folding unsigned  
idioms into unsigned loads.  They wouldn't be that hard for someone to  
add.

tom

On Jan 12, 2009, at 6:08 PM, Ulf Zibis wrote:

> Wow, these are good news.  :-)
>
> So is there a chance, to implement this behaviour in trunk, so we  
> could get rid of the +128 trick ?
> Is it also available for -client VM ?
>
> -Ulf
>
>
> Am 13.01.2009 02:39, John Rose schrieb:
>> On Jan 12, 2009, at 1:52 PM, Tom Rodriguez wrote:
>>
>>> The ideal for the simple example is something like (StoreC mem2  
>>> addr2 (AndI (LoadB mem1 addr1) (ConI 0xff))).  The code above will  
>>> break the match at the load, forcing the value into a register.   
>>> It's seem like an excessively strong cutout but I'm not sure how  
>>> to phrase it better, particularly since I don't know what exactly  
>>> what problem it designed to eliminate.  I believe it's probably  
>>> the anti-dep issue but without a concrete failure it's hard to  
>>> know what exactly it should look like.
>>
>> That sounds plausible.  In general, if a node has a unique user, it  
>> can be pulled into one of the little spanning trees that the  
>> matcher places over the ideal DAG.  The graph dump Christian sent  
>> shows that the LoadB has just one user ([[141]]) which means the  
>> matcher should be able to group the LoadB with the AndI (and  
>> transform to loadUB), unless there's something else going on, like  
>> the anti-deps you mention.
>>
>> -- John
>>
>>
>