cmd/compile: support pointers to arrays in arrayClear

Fixes #52635

Change-Id: I85f182931e30292983ef86c55a0ab6e01282395c
Reviewed-on: https://go-review.googlesource.com/c/go/+/403337
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>

src/cmd/compile/internal/walk/range.go

@@ -403,8 +403,14 @@ func arrayClear(loop *ir.RangeStmt, v1, v2, a ir.Node) ir.Node {
 		return nil
 	}
 	lhs := stmt.X.(*ir.IndexExpr)
+	x := lhs.X
+	if a.Type().IsPtr() && a.Type().Elem().IsArray() {
+		if s, ok := x.(*ir.StarExpr); ok && s.Op() == ir.ODEREF {
+			x = s.X
+		}
+	}
 
-	if !ir.SameSafeExpr(lhs.X, a) || !ir.SameSafeExpr(lhs.Index, v1) {
+	if !ir.SameSafeExpr(x, a) || !ir.SameSafeExpr(lhs.Index, v1) {
 		return nil
 	}
 

test/codegen/issue52635.go

@@ -0,0 +1,36 @@
+// asmcheck
+
+// Copyright 2022 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.
+
+// Test that optimized range memclr works with pointers to arrays.
+
+package codegen
+
+type T struct {
+	a *[10]int
+	b [10]int
+}
+
+func (t *T) f() {
+	// amd64:".*runtime.memclrNoHeapPointers"
+	for i := range t.a {
+		t.a[i] = 0
+	}
+
+	// amd64:".*runtime.memclrNoHeapPointers"
+	for i := range *t.a {
+		t.a[i] = 0
+	}
+
+	// amd64:".*runtime.memclrNoHeapPointers"
+	for i := range t.a {
+		(*t.a)[i] = 0
+	}
+
+	// amd64:".*runtime.memclrNoHeapPointers"
+	for i := range *t.a {
+		(*t.a)[i] = 0
+	}
+}