Newbie Question: How are the values set in a Sparc store instruction (e.g. STri)?

I’m a bit confused as to how some of the values in a Sparc store instruction actually come to be set. The Sparc backend defines a store as:

def STri : F3_2<3, 0b000100,
(outs), (ins MEMri:$addr, IntRegs:$src),
“st $src, [$addr]”,
[(store IntRegs:$src, ADDRri:$addr)]>;

F3_2 and it’s superclasses are defined as follows:

class F3_2<bits<2> opVal, bits<6> op3val, dag outs, dag ins,
string asmstr, list pattern> : F3<outs, ins, asmstr, pattern> {
bits<13> simm13;

let op = opVal;
let op3 = op3val;

let Inst{13} = 1; // i field = 1
let Inst{12-0} = simm13;

class F3<dag outs, dag ins, string asmstr, list pattern>
: InstSP<outs, ins, asmstr, pattern> {
bits<5> rd;
bits<6> op3;
bits<5> rs1;
let op{1} = 1; // Op = 2 or 3
let Inst{29-25} = rd;
let Inst{24-19} = op3;
let Inst{18-14} = rs1;

class InstSP<dag outs, dag ins, string asmstr, list pattern> : Instruction {
field bits<32> Inst;

let Namespace = “SP”;

bits<2> op;
let Inst{31-30} = op;

dag OutOperandList = outs;
dag InOperandList = ins;
let AsmString = asmstr;
let Pattern = pattern;

I cannot see how the values simm13, rd, and rs1 are actually set. While in some places in the .td file there are instructions prefixed with “let rd = …”, the store instructions are not. How do the register numbers/immediates get from $src and $addr to the relevant places in Inst?