cmd/compile: put constant value on node inside parentheses

That's where the unified IR writer expects it.

Fixes #73476

Change-Id: Ic22bd8dee5be5991e6d126ae3f6eccb2acdc0b19
Reviewed-on: https://go-review.googlesource.com/c/go/+/667415
Reviewed-by: Junyang Shao <shaojunyang@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Keith Randall <khr@google.com>
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Reviewed-by: Keith Randall <khr@google.com>

src/cmd/compile/internal/types2/range.go

@@ -37,6 +37,16 @@ func (check *Checker) rangeStmt(inner stmtContext, rangeStmt *syntax.ForStmt, no
 
 	if isTypes2 && x.mode != invalid && sValue == nil && !check.hasCallOrRecv {
 		if t, ok := arrayPtrDeref(under(x.typ)).(*Array); ok {
+			for {
+				// Put constant info on the thing inside parentheses.
+				// That's where (*../noder/writer).expr expects it.
+				// See issue 73476.
+				p, ok := rangeVar.(*syntax.ParenExpr)
+				if !ok {
+					break
+				}
+				rangeVar = p.X
+			}
 			// Override type of rangeVar to be a constant
 			// (and thus side-effects will not be computed
 			// by the backend).

src/go/types/range.go

@@ -40,6 +40,16 @@ func (check *Checker) rangeStmt(inner stmtContext, rangeStmt *ast.RangeStmt, noN
 
 	if isTypes2 && x.mode != invalid && sValue == nil && !check.hasCallOrRecv {
 		if t, ok := arrayPtrDeref(under(x.typ)).(*Array); ok {
+			for {
+				// Put constant info on the thing inside parentheses.
+				// That's where (*../noder/writer).expr expects it.
+				// See issue 73476.
+				p, ok := rangeVar.(*ast.ParenExpr)
+				if !ok {
+					break
+				}
+				rangeVar = p.X
+			}
 			// Override type of rangeVar to be a constant
 			// (and thus side-effects will not be computed
 			// by the backend).

test/fixedbugs/issue73476.go

@@ -0,0 +1,17 @@
+// run
+
+// Copyright 2025 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
+
+//go:noinline
+func f(p *[4]int) {
+	for i := range (*p) { // Note the parentheses! gofmt wants to remove them - don't let it!
+		println(i)
+	}
+}
+func main() {
+	f(nil)
+}

test/fixedbugs/issue73476.out

@@ -0,0 +1,4 @@
+0
+1
+2
+3