[dev.typeparams] cmd/compile: added a builtins.go test, fixed one bug

The builtins.go test is derived from
cmd/compile/internal/types2/testdata/check/builtins.go2, after removing
the error cases.  Added a few extra tests for len/cap/append.

Fixed one bug, which is that DELETE operations can't be transformed if
their argument is a typeparam. Also, the tranform of LEN/CAP calls does
not need to be delayed. Removed out-date references to the old
typechecker in the comments.

Change-Id: If7a21506a7ff63ff7c8e87ccd614ef4ff3a0d3c8
Reviewed-on: https://go-review.googlesource.com/c/go/+/336010
Run-TryBot: Dan Scales <danscales@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
Trust: Dan Scales <danscales@google.com>

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

@@ -126,22 +126,17 @@ func Call(pos src.XPos, typ *types.Type, fun ir.Node, args []ir.Node, dots bool)
 	}
 
 	if fun, ok := fun.(*ir.Name); ok && fun.BuiltinOp != 0 {
-		// For Builtin ops, we currently stay with using the old
-		// typechecker to transform the call to a more specific expression
-		// and possibly use more specific ops. However, for a bunch of the
-		// ops, we delay doing the old typechecker if any of the args have
-		// type params, for a variety of reasons:
+		// For most Builtin ops, we delay doing transformBuiltin if any of the
+		// args have type params, for a variety of reasons:
 		//
-		// OMAKE: hard to choose specific ops OMAKESLICE, etc. until arg type is known
-		// OREAL/OIMAG: can't determine type float32/float64 until arg type know
-		// OLEN/OCAP: old typechecker will complain if arg is not obviously a slice/array.
-		// OAPPEND: old typechecker will complain if arg is not obviously slice, etc.
-		//
-		// We will eventually break out the transforming functionality
-		// needed for builtin's, and call it here or during stenciling, as
-		// appropriate.
+		// OMAKE: transformMake can't choose specific ops OMAKESLICE, etc.
+		//    until arg type is known
+		// OREAL/OIMAG: transformRealImag can't determine type float32/float64
+		//    until arg type known
+		// OAPPEND: transformAppend requires that the arg is a slice
+		// ODELETE: transformDelete requires that the arg is a map
 		switch fun.BuiltinOp {
-		case ir.OMAKE, ir.OREAL, ir.OIMAG, ir.OLEN, ir.OCAP, ir.OAPPEND:
+		case ir.OMAKE, ir.OREAL, ir.OIMAG, ir.OAPPEND, ir.ODELETE:
 			hasTParam := false
 			for _, arg := range args {
 				if arg.Type().HasTParam() {

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

@@ -1270,7 +1270,7 @@ func (subst *subster) node(n ir.Node) ir.Node {
 				name := call.X.Name()
 				if name.BuiltinOp != ir.OXXX {
 					switch name.BuiltinOp {
-					case ir.OMAKE, ir.OREAL, ir.OIMAG, ir.OLEN, ir.OCAP, ir.OAPPEND:
+					case ir.OMAKE, ir.OREAL, ir.OIMAG, ir.OAPPEND, ir.ODELETE:
 						// Transform these builtins now that we
 						// know the type of the args.
 						m = transformBuiltin(call)

test/typeparam/builtins.go

@@ -0,0 +1,114 @@
+// compile -G=3
+
+// Copyright 2020 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// This file tests built-in calls on generic types.
+
+// derived and expanded from cmd/compile/internal/types2/testdata/check/builtins.go2
+
+package builtins
+
+// close
+
+type C0 interface{ int }
+type C1 interface{ chan int }
+type C2 interface{ chan int | <-chan int }
+type C3 interface{ chan int | chan float32 }
+type C4 interface{ chan int | chan<- int }
+type C5[T any] interface{ ~chan T | chan<- T }
+
+func _[T C1](ch T) {
+	close(ch)
+}
+
+func _[T C3](ch T) {
+	close(ch)
+}
+
+func _[T C4](ch T) {
+	close(ch)
+}
+
+func _[T C5[X], X any](ch T) {
+	close(ch)
+}
+
+// delete
+
+type M0 interface{ int }
+type M1 interface{ map[string]int }
+type M2 interface { map[string]int | map[string]float64 }
+type M3 interface{ map[string]int | map[rune]int }
+type M4[K comparable, V any] interface{ map[K]V | map[rune]V }
+
+func _[T M1](m T) {
+	delete(m, "foo")
+}
+
+func _[T M2](m T) {
+	delete(m, "foo")
+}
+
+func _[T M4[rune, V], V any](m T) {
+	delete(m, 'k')
+}
+
+// make
+
+type Bmc interface {
+	~map[rune]string | ~chan int
+}
+
+type Bms interface {
+	~map[string]int | ~[]int
+}
+
+type Bcs interface {
+	~chan bool | ~[]float64
+}
+
+type Bss interface {
+	~[]int | ~[]string
+}
+
+func _[T Bmc]() {
+	_ = make(T)
+	_ = make(T, 10)
+}
+
+func _[T Bms]() {
+	_ = make(T, 10)
+}
+
+func _[T Bcs]() {
+	_ = make(T, 10)
+}
+
+func _[T Bss]() {
+	_ = make(T, 10)
+	_ = make(T, 10, 20)
+}
+
+// len/cap
+
+type Slice[T any] interface {
+	type []T
+}
+
+func _[T any, S Slice[T]]() {
+	x := make(S, 5, 10)
+	_ = len(x)
+	_ = cap(x)
+}
+
+// append
+
+func _[T any, S Slice[T]]() {
+	x := make(S, 5)
+	y := make(S, 2)
+	var z T
+	_ = append(x, y...)
+	_ = append(x, z)
+}