[llvm] [RISCV][CostModel] Add getCFInstrCost RISC-V implementation (PR #65599)

[Sergey Kachkov via llvm-commits]

skachkov-sc wrote:

Changes for SPECInt2006:
```
Program                                                                 loop-vectorize.LoopsVectorized              
                                                                        before                         after  diff  
          test-suite :: External/SPEC/CINT2006/401.bzip2/401.bzip2.test  28.00                          28.00   0.0%
          test-suite :: External/SPEC/CINT2006/456.hmmer/456.hmmer.test  80.00                          80.00   0.0%
          test-suite :: External/SPEC/CINT2006/458.sjeng/458.sjeng.test   5.00                           5.00   0.0%
test-suite :: External/SPEC/CINT2006/462.libquantum/462.libquantum.test  16.00                          16.00   0.0%
      test-suite :: External/SPEC/CINT2006/471.omnetpp/471.omnetpp.test  14.00                          14.00   0.0%
          test-suite :: External/SPEC/CINT2006/473.astar/473.astar.test  22.00                          22.00   0.0%
  test-suite :: External/SPEC/CINT2006/483.xalancbmk/483.xalancbmk.test 193.00                         193.00   0.0%
      test-suite :: External/SPEC/CINT2006/464.h264ref/464.h264ref.test 287.00                         285.00  -0.7%
          test-suite :: External/SPEC/CINT2006/445.gobmk/445.gobmk.test 115.00                         114.00  -0.9%
              test-suite :: External/SPEC/CINT2006/403.gcc/403.gcc.test 183.00                         178.00  -2.7%
  test-suite :: External/SPEC/CINT2006/400.perlbench/400.perlbench.test  82.00                          74.00  -9.8%
              test-suite :: External/SPEC/CINT2006/429.mcf/429.mcf.test  11.00                           9.00 -18.2%
```

Example of loop in 429.mcf that is not vectorized now (looks indeed not very profitable):
```
for( arc = net->arcs; arc != (arc_t *)stop; arc++ )
{
    if( arc->flow )
    {
        if( !(arc->tail->number < 0 && arc->head->number > 0) )
        {
            if( !arc->tail->number )
            {
                operational_cost += (arc->cost - net->bigM);
                fleet++;
            }
            else
                operational_cost += arc->cost;
        }
    }

}
```

https://github.com/llvm/llvm-project/pull/65599