[LLVMdev] Inst field in MSP430InstrFormats.td

David Wiberg dwiberg at gmail.com
Sun Jul 21 16:19:28 PDT 2013


Within the file "MSP430InstrFormats.td" there is a class called
"MSP430Inst" which has "Instruction" as superclass. Within this class
there is a field called "Inst" (field bits<16> Inst;) which gets
assigned in classes which specifies a specific instruction format,
e.g. IForm contains:
  let Inst{12-15} = opcode;
  let Inst{7} = ad.Value;
  let Inst{6} = bw;
  let Inst{4-5} = as.Value;

>From what I can see these values does not propagate to the files
generated by TableGen. I have tried removing the field and it is at
least still possible to run llc on a simple input file. This leads to
a couple of questions:
1. Is this field redundant or does it have some use which I have missed?
2. What is the status of the MSP430 backend? In a mail from 2012
Anton indicates that it is usable but is it a good basis for backend

My goal is to implement support for a new target and one step on the
way is to fully understand how one of the existing backends work.


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