cmd/compile: drop TODO in NilCheck for riscv64

Also add log as arm/amd64 do.

Change-Id: I3698993e2df0ebf3bfcf8bad5fe389affa0e8eff
Reviewed-on: https://go-review.googlesource.com/c/go/+/595355
Reviewed-by: Keith Randall <[email protected]>
Reviewed-by: Robert Griesemer <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Keith Randall <[email protected]>

Author: mengzhuo

src/cmd/compile/internal/riscv64/ssa.go

@@ -7,6 +7,7 @@ package riscv64
 import (
 	"cmd/compile/internal/base"
 	"cmd/compile/internal/ir"
+	"cmd/compile/internal/logopt"
 	"cmd/compile/internal/objw"
 	"cmd/compile/internal/ssa"
 	"cmd/compile/internal/ssagen"
@@ -720,13 +721,15 @@ func ssaGenValue(s *ssagen.State, v *ssa.Value) {
 
 	case ssa.OpRISCV64LoweredNilCheck:
 		// Issue a load which will fault if arg is nil.
-		// TODO: optimizations. See arm and amd64 LoweredNilCheck.
 		p := s.Prog(riscv.AMOVB)
 		p.From.Type = obj.TYPE_MEM
 		p.From.Reg = v.Args[0].Reg()
 		ssagen.AddAux(&p.From, v)
 		p.To.Type = obj.TYPE_REG
 		p.To.Reg = riscv.REG_ZERO
+		if logopt.Enabled() {
+			logopt.LogOpt(v.Pos, "nilcheck", "genssa", v.Block.Func.Name)
+		}
 		if base.Debug.Nil != 0 && v.Pos.Line() > 1 { // v.Pos == 1 in generated wrappers
 			base.WarnfAt(v.Pos, "generated nil check")
 		}