cmd/compiler: make decompose shortcuts apply for PtrShaped, not just Ptr

The immediate-data interface shortcuts also apply to pointer-shaped
things like maps, channels, and functions.

Fixes #63505.

Change-Id: I43982441bf523f53e9e5d183e95aea7c6655dd6b
Reviewed-on: https://go-review.googlesource.com/c/go/+/534657
TryBot-Result: Gopher Robot <[email protected]>
Run-TryBot: David Chase <[email protected]>
Auto-Submit: David Chase <[email protected]>
Reviewed-by: Cuong Manh Le <[email protected]>
Reviewed-by: Cherry Mui <[email protected]>

src/cmd/compile/internal/ssa/_gen/dec.rules

@@ -118,12 +118,12 @@
 // More annoying case: (ArraySelect[0] (StructSelect[0] isAPtr))
 // There, result of the StructSelect is an Array (not a pointer) and
 // the pre-rewrite input to the ArraySelect is a struct, not a pointer.
-(StructSelect [0] x) && x.Type.IsPtr()  => x
-(ArraySelect [0] x) && x.Type.IsPtr()  => x
+(StructSelect [0] x) && x.Type.IsPtrShaped()  => x
+(ArraySelect [0] x) && x.Type.IsPtrShaped()  => x
 
 // These, too.  Bits is bits.
-(ArrayMake1 x) && x.Type.IsPtr() => x
-(StructMake1 x) && x.Type.IsPtr() => x
+(ArrayMake1 x) && x.Type.IsPtrShaped() => x
+(StructMake1 x) && x.Type.IsPtrShaped() => x
 
 (Store dst (StructMake1 <t> f0) mem) =>
   (Store {t.FieldType(0)} (OffPtr <t.FieldType(0).PtrTo()> [0] dst) f0 mem)

test/fixedbugs/issue63505.go

@@ -0,0 +1,45 @@
+// compile
+
+// Copyright 2023 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
+
+type explainer struct {
+	m map[string]string
+}
+
+func init() {
+	RegisterExplainer(newExplainer())
+}
+
+type Explainer interface {
+	Name() string
+	Map() map[string]string
+}
+
+func (e explainer) Name() string {
+	return "HelloWorldExplainer"
+}
+
+func (e explainer) Map() map[string]string {
+	return e.m
+}
+
+//go:noinline
+func newExplainer() explainer {
+	m := make(map[string]string)
+	m["Hello"] = "World!"
+	return explainer{m}
+}
+
+var explainers = make(map[string]Explainer)
+
+func RegisterExplainer(e Explainer) {
+	explainers[e.Name()] = e
+}
+
+func main() {
+
+}