[LLVMdev] LLVM Newbie. Questions about backend.

[Sami Ahlberg]

Hello,
I have been studying LLVM and started to create a new backend for a  
new RISC architecture. Now I need some help to get forward with my  
project. I'm quite new to compiling techniques so I'm sorry for the  
stupid questions.

Question 1:
My idea is to lower the select SDNode as follows:

%res1 = %falseVal
%res2 = setc %trueVal, %condition

Where setc is conditional mov. The question is how can I make sure  
that %res1 and %res2 are assigned to the same phsyical register? (I'm  
assuming you can only define virtual register once, is this correct  
assumption?)

Question 2:
What kind of information if any the front end needs about the target  
architecture? Am I able to use gcc front end to compile for the new  
architecture and what if there are 32- and 64-bit versions of the  
architecture? Is there an alternative front end and how does that  
handle the same issues?


Thank you very much in advance for your answers,

Sami