[LLVMdev] ISRs for PIC16 [was [llvm]r79631 ...]

[Sanjiv Gupta]

Bringing it up again.

- Sanjiv
Sanjiv Gupta wrote:
> Chris Lattner wrote:
>   
>> We should discuss this on llvmdev, I think it came up before but there 
>> was no conclusive plan that was proposed.
>>     
> The approach that we thought for PIC16 can be described in a 
> single line as below.
>
> "Keep the functions called from ISR and main separate by cloning the  
> shared ones".
>
>   
>> In short, I think that this sort of thing should be modeled as an 
>> attribute on function definitions, not declarations.  I don't 
>> understand why you need to clone entire call graphs, but this is best 
>> discussed on llvmdev.
>>     
> It isn't cloning the entire call graph. It's cloning only the shared 
> ones as mentioned above.
>
> The information that a function is ISR is encoded in the section string 
> for the lack of a better attribute.
>
> Plus we also wanted to encode some information to inform codegen about 
> whether we are codegenerating an interrupt line function. Again the 
> section string is used to encode the same. Probably annotations might be 
> a better place but that does not work currently (and also, accessing 
> them slower). This information is required so that the codegen can emit 
> calls to appropriate intrinsics.
>
> So, IMO, the approach is simple, but probably the implementation wasn't 
> clean.
>
> Ideas welcome.
>