Re: m68k bootstrap problem

[Kenneth Zadeck <zadeck at naturalbridge dot com>]

Roman Zippel wrote:
> Hi,
>
> On Wed, 20 Jun 2007, Kenneth Zadeck wrote:
>
>   
>> If we add the dead note there we are asserting that the value is
>> modified by the caller. however it might not be and someone could write
>> a piece of asm right after the call to use that reg if the person knew
>> that the reg was not modified by that particular call.
>>     
>
> I have big problems to see this as a valid example, this sounds just 
> broken. First off the user had to know the register was alive before and 
> then the user had to magically know the register isn't clobbered by the 
> call (e.g. loading the address of the function into that register).
> You could declare the variable as asm register variable, then it might 
> work, but then the register wouldn't be available for allocation anyway 
> and the whole problem changes.
>
>   
>> having the dead note there is asserting to the register allocator that
>> they are free to use that reg after the calll in any way that it wants
>> and there is a (small) possibility that is wrong.
>>     
>
> IMO there is nothing wrong with this.
>
> bye, Roman
>   
The whole reason for bugzilla is to remind compiler developers that rare
case cannot be ignored.

kenny