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>

2 files changed, 46 insertions, 0 deletions

diff --git a/test/typeparam/issue48094.dir/a.go b/test/typeparam/issue48094.dir/a.go
new file mode 100644
index 0000000000..dd8c16f3ae
--- /dev/null
+++ b/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)
+//}
diff --git a/test/typeparam/issue48094.dir/main.go b/test/typeparam/issue48094.dir/main.go
new file mode 100644
index 0000000000..eb1ddbe231
--- /dev/null
+++ 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")
+	//}
+}