[dev.typeparams] cmd/compile: add -d=unified flag to enable unified IR

This CL adds a new -d=unified debug flag, which controls whether
unified IR mode is used.

Change-Id: Iaa5f3cc0a24b9881aeec5317cd6b462b4a7b6fc9
Reviewed-on: https://go-review.googlesource.com/c/go/+/327054
Trust: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Robert Griesemer <gri@golang.org>

src/cmd/compile/internal/base/debug.go

@@ -46,6 +46,7 @@ type DebugFlags struct {
 	SoftFloat            int    `help:"force compiler to emit soft-float code"`
 	TypeAssert           int    `help:"print information about type assertion inlining"`
 	TypecheckInl         int    `help:"eager typechecking of inline function bodies"`
+	Unified              int    `help:"enable unified IR construction"`
 	WB                   int    `help:"print information about write barriers"`
 	ABIWrap              int    `help:"print information about ABI wrapper generation"`
 

src/cmd/compile/internal/noder/noder.go

@@ -76,6 +76,11 @@ func LoadPackage(filenames []string) {
 	}
 	base.Timer.AddEvent(int64(lines), "lines")
 
+	if base.Debug.Unified != 0 {
+		useUnifiedIR(noders)
+		return
+	}
+
 	if base.Flag.G != 0 {
 		// Use types2 to type-check and possibly generate IR.
 		check2(noders)

src/cmd/compile/internal/reflectdata/reflect.go

@@ -1780,6 +1780,10 @@ func methodWrapper(rcvr *types.Type, method *types.Field, forItab bool) *obj.LSy
 		// TODO: check that we do the right thing when rcvr.IsInterface().
 		generic = true
 	}
+	if base.Debug.Unified != 0 {
+		// TODO(mdempsky): Support dictionaries for unified IR.
+		generic = false
+	}
 	newnam := ir.MethodSym(rcvr, method.Sym)
 	lsym := newnam.Linksym()
 	if newnam.Siggen() {