cmd/compile: builtins may be in the unsafe package

Now that unsafe.Sizeof and friends can operate on generic parameters,
and evaluate to non-constants, we need to export/import them correctly.

Fixes #48094

Change-Id: If3ebf77255385cd5462e13fb7ced8b157ba3cf5b
Reviewed-on: https://go-review.googlesource.com/c/go/+/346469
Trust: Keith Randall <khr@golang.org>
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>

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

@@ -1692,6 +1692,7 @@ func (w *exportWriter) expr(n ir.Node) {
 		isBuiltin := n.BuiltinOp != ir.OXXX
 		w.bool(isBuiltin)
 		if isBuiltin {
+			w.bool(n.Sym().Pkg == types.UnsafePkg)
 			w.string(n.Sym().Name)
 			break
 		}

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

@@ -1269,7 +1269,11 @@ func (r *importReader) node() ir.Node {
 	case ir.ONAME:
 		isBuiltin := r.bool()
 		if isBuiltin {
-			return types.BuiltinPkg.Lookup(r.string()).Def.(*ir.Name)
+			pkg := types.BuiltinPkg
+			if r.bool() {
+				pkg = types.UnsafePkg
+			}
+			return pkg.Lookup(r.string()).Def.(*ir.Name)
 		}
 		return r.localName()
 

test/typeparam/issue48094.dir/a.go

@@ -0,0 +1,26 @@
+// 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
+
+import "unsafe"
+
+func F[T any]() uintptr {
+	var t T
+	return unsafe.Sizeof(t)
+}
+
+func G[T any]() uintptr {
+	var t T
+	return unsafe.Alignof(t)
+}
+
+//func H[T any]() uintptr {
+//	type S struct {
+//		a T
+//		b T
+//	}
+//	var s S
+//	return unsafe.Offsetof(s.b)
+//}

test/typeparam/issue48094.dir/main.go

@@ -0,0 +1,20 @@
+// 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"
+
+func main() {
+	if a.F[int64]() != 8 {
+		panic("bad")
+	}
+	if a.G[int8]() != 1 {
+		panic("bad")
+	}
+	// TODO: enable once 47631 is fixed.
+	//if a.H[int64]() != 8 {
+	//	panic("bad")
+	//}
+}

test/typeparam/issue48094.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