Re: revised patch committed.

[Kenneth Zadeck <zadeck at naturalbridge dot com>]

Amir Gonnen wrote:
> At first I though the df_scan patch unveiled this bug, but now I see
> this bug happens regardless.
> Even without the patch, once my code generates zero_extract on the set
> destination, dse creates wrong code.
>
> Amir
>
>   
>> So if I understand correctly the patch changes a missed optimization
>> bug to wrong code?
>>
>> Paolo
>>
>>     
The main reason that this was missed was that there are no public,
active ports that actually do this.  I accepted the patch on Ian
Taylor's (iant) advice because he said that it was legal as long as the
mem was a single byte.   Iant claimed that the last machine that could
do this kind of thing was the 68k but in his comments he did not
actually say if the gcc port actually did it.   Thus, you are really on
your own as to finding out how much else is broken to support this feature.

When we test new passes, and I admit to being the person who wrote much
of dse, we test them on the active ports and we fix bugs against those
ports.   But a project like gcc is really a use it or loose it kind of
system.   The features that are exercised on the public active ports
work, and the features that are not exercised tend to rot, generally
until someone adds a new port that utilizes the feature. 

I think that the policy is that we accept patches from private ports as
long as they are fix problems with things that are supposed to work.  
Certainly no one has pushed back on me for accepting your first patch.  

Kenny