[dev.typeparams] cmd/compile: do transformCall with non-shape type of call

Do the transformCall using the original types2-derived type of the call
(in particular, the types of the params as non-shapes). Currently, since
we were using the param types of the instantiation, we might add in
interface conversions to an interface with shapes in the one case of a
full-instantiated generic call. So, we do the transformCall() before
installing the shaped-based instantiation. transformCall() works
correctly even in the case of OCALL/FUNCINST.

Fixed two related bugs:
  - Fixed case where we still were not correctly substituting the types
    for a function instantiation.
  - The type substituter needs to copy field flags while substituting in
    tstruct.

Change-Id: I14e960737d6840a75846ede480e6650534ba3af3
Reviewed-on: https://go-review.googlesource.com/c/go/+/340259
Trust: Dan Scales <danscales@google.com>
Run-TryBot: Dan Scales <danscales@google.com>
Reviewed-by: Keith Randall <khr@golang.org>

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

@@ -125,13 +125,17 @@ func (g *irgen) expr0(typ types2.Type, expr syntax.Expr) ir.Node {
 			}
 			if fun.Op() == ir.OFUNCINST {
 				// Replace explicit type args with the full list that
-				// includes the additional inferred type args
+				// includes the additional inferred type args.
+				// Substitute the type args for the type params in
+				// the generic function's type.
 				fun.(*ir.InstExpr).Targs = targs
+				newt := g.substType(fun.Type(), fun.Type().TParams(), targs)
+				typed(newt, fun)
 			} else {
 				// Create a function instantiation here, given there
 				// are only inferred type args (e.g. min(5,6), where
 				// min is a generic function). Substitute the type
-				// args for the type params in the uninstantiated function's
+				// args for the type params in the generic function's
 				// type.
 				inst := ir.NewInstExpr(pos, ir.OFUNCINST, fun, targs)
 				newt := g.substType(fun.Type(), fun.Type().TParams(), targs)

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

@@ -119,6 +119,14 @@ func (g *irgen) stencil() {
 						fmt.Printf("%s in %v at generic function call: %v - %v\n", dictkind, decl, inst.X, call)
 					}
 				}
+
+				// Transform the Call now, which changes OCALL to
+				// OCALLFUNC and does typecheckaste/assignconvfn. Do
+				// it before installing the instantiation, so we are
+				// checking against non-shape param types in
+				// typecheckaste.
+				transformCall(call)
+
 				// Replace the OFUNCINST with a direct reference to the
 				// new stenciled function
 				call.X = st.Nname
@@ -132,9 +140,6 @@ func (g *irgen) stencil() {
 
 				// Add dictionary to argument list.
 				call.Args.Prepend(dictValue)
-				// Transform the Call now, which changes OCALL
-				// to OCALLFUNC and does typecheckaste/assignconvfn.
-				transformCall(call)
 				modified = true
 			}
 			if n.Op() == ir.OCALLMETH && n.(*ir.CallExpr).X.Op() == ir.ODOTMETH && len(deref(n.(*ir.CallExpr).X.Type().Recv().Type).RParams()) > 0 {

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

@@ -130,7 +130,8 @@ func transformConvCall(n *ir.CallExpr) ir.Node {
 }
 
 // transformCall transforms a normal function/method call. Corresponds to last half
-// (non-conversion, non-builtin part) of typecheck.tcCall.
+// (non-conversion, non-builtin part) of typecheck.tcCall. This code should work even
+// in the case of OCALL/OFUNCINST.
 func transformCall(n *ir.CallExpr) {
 	// n.Type() can be nil for calls with no return value
 	assert(n.Typecheck() == 1)

src/cmd/compile/internal/typecheck/subr.go

@@ -1278,6 +1278,12 @@ func (ts *Tsubster) tstruct(t *types.Type, force bool) *types.Type {
 			// the type param, not the instantiated type).
 			newfields[i] = types.NewField(f.Pos, f.Sym, t2)
 			newfields[i].Embedded = f.Embedded
+			if f.IsDDD() {
+				newfields[i].SetIsDDD(true)
+			}
+			if f.Nointerface() {
+				newfields[i].SetNointerface(true)
+			}
 			if f.Nname != nil && ts.Vars != nil {
 				v := ts.Vars[f.Nname.(*ir.Name)]
 				if v != nil {