[dev.typeparams] Don't check typecheck(3) on transform, so no need to export/import it

We have a value typecheck(3) that indicates that a node in a generic
function still needs transformation (via the functions in transform.go).
But it is not very desirable to export/import the value of typecheck(3).
So, I changed the stenciling code to just try to transform all relevant
node types during node copy. Almost all tranform functions were already
idempotent. I only had to add an extra if check before calling
transformAssign() in the OAS case. We still use the typecheck(3) in
noder to determine when higher-nodes have to delay transformation
because one or more of their args are delaying transformation.

Added new test mapsimp.go that required these tranformations after import.

As an additional change, export/import of OINDEX requires exporting the
type using w.exoticType() rather than w.typ(), in order to handle
generic functions. Since generic functions can have pre-transform
operations, the index operation can have a tuple type (multiple return
from a map lookup).

Added printing of imported function bodies in -W=3 debug mode.

Change-Id: I220e2428dc5f2741e91db146f075eb5b6045f451
Reviewed-on: https://go-review.googlesource.com/c/go/+/322191
Trust: Dan Scales <danscales@google.com>
Run-TryBot: Dan Scales <danscales@google.com>
Reviewed-by: Keith Randall <khr@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>

3 files changed, 37 insertions, 35 deletions

diff --git a/src/cmd/compile/internal/noder/stencil.go b/src/cmd/compile/internal/noder/stencil.go
index 67580add73..e273a80b20 100644
--- a/src/cmd/compile/internal/noder/stencil.go
+++ b/src/cmd/compile/internal/noder/stencil.go
@@ -374,45 +374,43 @@ func (subst *subster) node(n ir.Node) ir.Node {
 		}
 		ir.EditChildren(m, edit)
 
-		if x.Typecheck() == 3 {
-			// These are nodes whose transforms were delayed until
-			// their instantiated type was known.
-			m.SetTypecheck(1)
-			if typecheck.IsCmp(x.Op()) {
-				transformCompare(m.(*ir.BinaryExpr))
-			} else {
-				switch x.Op() {
-				case ir.OSLICE, ir.OSLICE3:
-					transformSlice(m.(*ir.SliceExpr))
-
-				case ir.OADD:
-					m = transformAdd(m.(*ir.BinaryExpr))
-
-				case ir.OINDEX:
-					transformIndex(m.(*ir.IndexExpr))
-
-				case ir.OAS2:
-					as2 := m.(*ir.AssignListStmt)
-					transformAssign(as2, as2.Lhs, as2.Rhs)
-
-				case ir.OAS:
-					as := m.(*ir.AssignStmt)
+		m.SetTypecheck(1)
+		if typecheck.IsCmp(x.Op()) {
+			transformCompare(m.(*ir.BinaryExpr))
+		} else {
+			switch x.Op() {
+			case ir.OSLICE, ir.OSLICE3:
+				transformSlice(m.(*ir.SliceExpr))
+
+			case ir.OADD:
+				m = transformAdd(m.(*ir.BinaryExpr))
+
+			case ir.OINDEX:
+				transformIndex(m.(*ir.IndexExpr))
+
+			case ir.OAS2:
+				as2 := m.(*ir.AssignListStmt)
+				transformAssign(as2, as2.Lhs, as2.Rhs)
+
+			case ir.OAS:
+				as := m.(*ir.AssignStmt)
+				if as.Y != nil {
+					// transformAssign doesn't handle the case
+					// of zeroing assignment of a dcl (rhs[0] is nil).
 					lhs, rhs := []ir.Node{as.X}, []ir.Node{as.Y}
 					transformAssign(as, lhs, rhs)
+				}
 
-				case ir.OASOP:
-					as := m.(*ir.AssignOpStmt)
-					transformCheckAssign(as, as.X)
+			case ir.OASOP:
+				as := m.(*ir.AssignOpStmt)
+				transformCheckAssign(as, as.X)
 
-				case ir.ORETURN:
-					transformReturn(m.(*ir.ReturnStmt))
+			case ir.ORETURN:
+				transformReturn(m.(*ir.ReturnStmt))
 
-				case ir.OSEND:
-					transformSend(m.(*ir.SendStmt))
+			case ir.OSEND:
+				transformSend(m.(*ir.SendStmt))
 
-				default:
-					base.Fatalf("Unexpected node with Typecheck() == 3")
-				}
 			}
 		}
 
diff --git a/src/cmd/compile/internal/typecheck/iexport.go b/src/cmd/compile/internal/typecheck/iexport.go
index d956ada3c5..292bb2c409 100644
--- a/src/cmd/compile/internal/typecheck/iexport.go
+++ b/src/cmd/compile/internal/typecheck/iexport.go
@@ -1735,7 +1735,7 @@ func (w *exportWriter) expr(n ir.Node) {
 		w.expr(n.X)
 		w.expr(n.Index)
 		if go117ExportTypes {
-			w.typ(n.Type())
+			w.exoticType(n.Type())
 			if n.Op() == ir.OINDEXMAP {
 				w.bool(n.Assigned)
 			}
diff --git a/src/cmd/compile/internal/typecheck/iimport.go b/src/cmd/compile/internal/typecheck/iimport.go
index 966e865630..d5b549483d 100644
--- a/src/cmd/compile/internal/typecheck/iimport.go
+++ b/src/cmd/compile/internal/typecheck/iimport.go
@@ -1025,6 +1025,10 @@ func (r *importReader) funcBody(fn *ir.Func) {
 	fn.Inl.Body = body
 
 	r.curfn = outerfn
+	if base.Flag.W >= 3 {
+		fmt.Printf("Imported for %v", fn)
+		ir.DumpList("", fn.Inl.Body)
+	}
 }
 
 func (r *importReader) readNames(fn *ir.Func) []*ir.Name {
@@ -1349,7 +1353,7 @@ func (r *importReader) node() ir.Node {
 		n := ir.NewIndexExpr(r.pos(), r.expr(), r.expr())
 		if go117ExportTypes {
 			n.SetOp(op)
-			n.SetType(r.typ())
+			n.SetType(r.exoticType())
 			if op == ir.OINDEXMAP {
 				n.Assigned = r.bool()
 			}