From 3452d80da3cf4f08da0f5905b1aa19cec475936e Mon Sep 17 00:00:00 2001
From: Keith Randall <khr@golang.org>
Date: Thu, 24 Apr 2025 08:38:56 -0700
Subject: [PATCH] cmd/compile: add cast in range loop final value computation
When replacing a loop where the iteration variable has a named type,
we need to compute the last iteration value as i = T(len(a)-1), not
just i = len(a)-1.
Fixes #73491
Change-Id: Ic1cc3bdf8571a40c10060f929a9db8a888de2b70
Reviewed-on: https://go-review.googlesource.com/c/go/+/667815
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Keith Randall <khr@google.com>
Reviewed-by: Junyang Shao <shaojunyang@google.com>
Reviewed-by: Keith Randall <khr@google.com>
---
src/cmd/compile/internal/walk/range.go | 2 +-
test/fixedbugs/issue73491.go | 25 +++++++++++++++++++++++++
2 files changed, 26 insertions(+), 1 deletion(-)
create mode 100644 test/fixedbugs/issue73491.go
diff --git a/src/cmd/compile/internal/walk/range.go b/src/cmd/compile/internal/walk/range.go
index a1e5442a69e..3d3547b84b5 100644
--- a/src/cmd/compile/internal/walk/range.go
+++ b/src/cmd/compile/internal/walk/range.go
@@ -605,7 +605,7 @@ func arrayClear(wbPos src.XPos, a ir.Node, nrange *ir.RangeStmt) ir.Node {
// For array range clear, also set "i = len(a) - 1"
if nrange != nil {
- idx := ir.NewAssignStmt(base.Pos, nrange.Key, ir.NewBinaryExpr(base.Pos, ir.OSUB, ir.NewUnaryExpr(base.Pos, ir.OLEN, a), ir.NewInt(base.Pos, 1)))
+ idx := ir.NewAssignStmt(base.Pos, nrange.Key, typecheck.Conv(ir.NewBinaryExpr(base.Pos, ir.OSUB, ir.NewUnaryExpr(base.Pos, ir.OLEN, a), ir.NewInt(base.Pos, 1)), nrange.Key.Type()))
n.Body.Append(idx)
}
diff --git a/test/fixedbugs/issue73491.go b/test/fixedbugs/issue73491.go
new file mode 100644
index 00000000000..4137088bded
--- /dev/null
+++ b/test/fixedbugs/issue73491.go
@@ -0,0 +1,25 @@
+// build
+
+// 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
+
+type T int
+
+const K T = 5
+
+type P struct {
+ a [K]*byte
+}
+
+//go:noinline
+func f(p *P) {
+ for i := range K {
+ p.a[i] = nil
+ }
+}
+func main() {
+ f(nil)
+}
--
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