[Question] How to deliver loop-related pragma information from TREE to RTL?

[Yangfei (Felix)]

Hello everyone,

    I'm thinking of the right way of adding some loop related pragmas to GCC. 
    An example:

    #pragma loop unroll = 2
    for (i = 0; i < n; i ++)
      {
        Whatever...
      }

    Here I want the unroll factor of the loop to be 2 when doing RTL loop unrolling. 
    But I find that it's kind of difficult to achieve this in GCC. 
    The reason is that the loop structures are initialized and finalized at run time. Also the RTL expand phase is kind of complex and it does not care about loops. 
    So how to deliver the pragma information to RTL loop unrolling pass? What the the elegant way of doing this? 
    Can anyone give some suggestions on this please? 
    Many thanks.