cmd/compile: fixes for non-constant Sizeof/Alignof/Offsetof

Includes Robert's suggested fix in validate.go to not fail on
non-constant alignof/offsetof/sizeof calls. Further changes to wait on
transforming these calls until stenciling time, when we can call
EvalConst() to evaluate them once all the relevant types are known.

Added a bunch of new tests for non-constant Sizeof/Alignof/Offsetof.

Fixes #47716

Change-Id: I469af888eb9ce3a853124d919eda753971009b3e
Reviewed-on: https://go-review.googlesource.com/c/go/+/344250
Run-TryBot: Dan Scales <danscales@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>
Trust: Dan Scales <danscales@google.com>

1 files changed, 68 insertions, 0 deletions

diff --git a/test/typeparam/issue47716.go b/test/typeparam/issue47716.go
new file mode 100644
index 0000000000..7f34fcb21f
--- /dev/null
+++ b/test/typeparam/issue47716.go
@@ -0,0 +1,68 @@
+// run -gcflags=-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 main
+
+import (
+	"fmt"
+	"unsafe"
+)
+
+// size returns the size of type T
+func size[T any](x T) uintptr {
+	return unsafe.Sizeof(x)
+}
+
+// size returns the alignment of type T
+func align[T any](x T) uintptr {
+	return unsafe.Alignof(x)
+}
+
+type Tstruct[T any] struct {
+	f1 T
+	f2 int
+}
+
+// offset returns the offset of field f2 in the generic type Tstruct
+func (r *Tstruct[T]) offset() uintptr {
+	return unsafe.Offsetof(r.f2)
+}
+
+func main() {
+	v1 := int(5)
+	if got, want := size(v1), unsafe.Sizeof(v1); got != want {
+		panic(fmt.Sprintf("got %d, want %d", got, want))
+	}
+	if got, want := align(v1), unsafe.Alignof(v1); got != want {
+		panic(fmt.Sprintf("got %d, want %d", got, want))
+	}
+
+	v2 := "abc"
+	if got, want := size(v2), unsafe.Sizeof(v2); got != want {
+		panic(fmt.Sprintf("got %d, want %d", got, want))
+	}
+	if got, want := align(v2), unsafe.Alignof(v2); got != want {
+		panic(fmt.Sprintf("got %d, want %d", got, want))
+	}
+
+	var v3 Tstruct[int]
+	if got, want := unsafe.Offsetof(v3.f2), unsafe.Sizeof(v1); got != want {
+		panic(fmt.Sprintf("got %d, want %d", got, want))
+	}
+
+	var v4 Tstruct[interface{}]
+	var v5 interface{}
+	if got, want := unsafe.Offsetof(v4.f2), unsafe.Sizeof(v5); got != want {
+		panic(fmt.Sprintf("got %d, want %d", got, want))
+	}
+
+	if got, want := v3.offset(), unsafe.Offsetof(v3.f2); got != want {
+		panic(fmt.Sprintf("got %d, want %d", got, want))
+	}
+	if got, want := v4.offset(), unsafe.Offsetof(v4.f2); got != want {
+		panic(fmt.Sprintf("got %d, want %d", got, want))
+	}
+}