[dev.typeparams] cmd/compile: add import/export of calls to builtin functions

For generic functions, we have to leave the builtins in OCALL form,
rather than transform to specific ops, since we don't know the exact
types involved. Allow export/import of builtins in OCALL form.

Added new export/import test mapimp.go.

Change-Id: I571f8eeaa13b4f69389dbdb9afb6cc61924b9bf2
Reviewed-on: https://go-review.googlesource.com/c/go/+/321750
Trust: Dan Scales <danscales@google.com>
Reviewed-by: Keith Randall <khr@golang.org>

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

@@ -1579,6 +1579,16 @@ func (w *exportWriter) expr(n ir.Node) {
 		// We don't need a type here, as the type will be provided at the
 		// declaration of n.
 		w.op(ir.ONAME)
+
+		// This handles the case where we haven't yet transformed a call
+		// to a builtin, so we must write out the builtin as a name in the
+		// builtin package.
+		isBuiltin := n.BuiltinOp != ir.OXXX
+		w.bool(isBuiltin)
+		if isBuiltin {
+			w.string(n.Sym().Name)
+			break
+		}
 		w.localName(n)
 
 	// case OPACK, ONONAME:

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

@@ -1184,6 +1184,10 @@ func (r *importReader) node() ir.Node {
 		return n
 
 	case ir.ONAME:
+		isBuiltin := r.bool()
+		if isBuiltin {
+			return types.BuiltinPkg.Lookup(r.string()).Def.(*ir.Name)
+		}
 		return r.localName()
 
 	// case OPACK, ONONAME:

test/typeparam/mapimp.dir/a.go

@@ -0,0 +1,15 @@
+// Copyright 2021 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.
+
+package a
+
+// Map calls the function f on every element of the slice s,
+// returning a new slice of the results.
+func Mapper[F, T any](s []F, f func(F) T) []T {
+        r := make([]T, len(s))
+        for i, v := range s {
+                r[i] = f(v)
+        }
+        return r
+}

test/typeparam/mapimp.dir/main.go

@@ -0,0 +1,28 @@
+// Copyright 2021 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.
+
+package main
+
+import (
+	"a"
+	"fmt"
+	"reflect"
+	"strconv"
+)
+
+func main() {
+	got := a.Mapper([]int{1, 2, 3}, strconv.Itoa)
+	want := []string{"1", "2", "3"}
+	if !reflect.DeepEqual(got, want) {
+		panic(fmt.Sprintf("got %s, want %s", got, want))
+	}
+
+	fgot := a.Mapper([]float64{2.5, 2.3, 3.5}, func(f float64) string {
+		return strconv.FormatFloat(f, 'f', -1, 64)
+	})
+	fwant := []string{"2.5", "2.3", "3.5"}
+	if !reflect.DeepEqual(fgot, fwant) {
+		panic(fmt.Sprintf("got %s, want %s", fgot, fwant))
+	}
+}

test/typeparam/mapimp.go

@@ -0,0 +1,7 @@
+// rundir -G=3
+
+// Copyright 2021 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.
+
+package ignored