Revert "cmd/compile: inline convI2E"

This reverts commit 395d36a6.

Appears to be responsible for builder failures.

Change-Id: Ic6c6307f662767e529060b88704a9f074785d99e
Reviewed-on: https://go-review.googlesource.com/31310
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Austin Clements <austin@google.com>

src/cmd/compile/internal/gc/builtin/runtime.go

@@ -58,6 +58,7 @@ func slicecopy(to any, fr any, wid uintptr) int
 func slicestringcopy(to any, fr any) int
 
 // interface conversions
+func convI2E(elem any) (ret any)
 func convI2I(typ *byte, elem any) (ret any)
 func convT2E(typ *byte, elem *any) (ret any)
 func convT2I(tab *byte, elem *any) (ret any)

src/cmd/compile/internal/gc/walk.go

@@ -410,14 +410,16 @@ func walkexprlistcheap(s []*Node, init *Nodes) {
 	}
 }
 
-// Build name of function for interface conversion.
+// Build name of function: convI2E etc.
 // Not all names are possible
-// (e.g., we'll never generate convE2E or convE2I or convI2E).
+// (e.g., we'll never generate convE2E or convE2I).
 func convFuncName(from, to *Type) string {
 	tkind := to.iet()
 	switch from.iet() {
 	case 'I':
 		switch tkind {
+		case 'E':
+			return "convI2E"
 		case 'I':
 			return "convI2I"
 		}
@@ -1078,34 +1080,6 @@ opswitch:
 			break
 		}
 
-		// Implement interface to empty interface conversion.
-		// tmp = i.itab
-		// if tmp != nil {
-		//    tmp = tmp.type
-		// }
-		// e = iface{tmp, i.data}
-		if n.Type.IsEmptyInterface() && n.Left.Type.IsInterface() && !n.Left.Type.IsEmptyInterface() {
-			// Evaluate the input interface.
-			c := temp(n.Left.Type)
-			init.Append(nod(OAS, c, n.Left))
-
-			// Get the itab out of the interface.
-			tmp := temp(ptrto(Types[TUINT8]))
-			init.Append(nod(OAS, tmp, typecheck(nod(OITAB, c, nil), Erv)))
-
-			// Get the type out of the itab.
-			nif := nod(OIF, typecheck(nod(ONE, tmp, nodnil()), Erv), nil)
-			nif.Nbody.Set1(nod(OAS, tmp, itabType(tmp)))
-			init.Append(nif)
-
-			// Build the result.
-			e := nod(OEFACE, tmp, ifaceData(c, ptrto(Types[TUINT8])))
-			e.Type = n.Type // assign type manually, typecheck doesn't understand OEFACE.
-			e.Typecheck = 1
-			n = e
-			break
-		}
-
 		var ll []*Node
 		if n.Type.IsEmptyInterface() {
 			if !n.Left.Type.IsInterface() {

src/runtime/iface.go

@@ -264,6 +264,16 @@ func assertE2T2(t *_type, e eface, r unsafe.Pointer) bool {
 	return true
 }
 
+func convI2E(i iface) (r eface) {
+	tab := i.tab
+	if tab == nil {
+		return
+	}
+	r._type = tab._type
+	r.data = i.data
+	return
+}
+
 func assertI2E(inter *interfacetype, i iface, r *eface) {
 	tab := i.tab
 	if tab == nil {