From 7015ed891c6f4e51ebaa642fce42ea8a1592b4e1 Mon Sep 17 00:00:00 2001
From: Mauri de Souza Meneguzzo <mauri870@gmail.com>
Date: Fri, 1 Sep 2023 18:26:49 +0000
Subject: sync: prevent (*Map).Range from always escaping

After the change from CL 426074 the Range method on Map always
escape the read variable, leading to an allocation.

Since the compiler doesn't do live-range splitting for local variables we
need to use some hints to only escape in that particular branch.

Fixes #62404

Change-Id: I938a5e593647455fa827e3dd3ed8ea22c7365df1
GitHub-Last-Rev: fcbedb467c7b4e6f1d49e299d243cad70deb34e9
GitHub-Pull-Request: golang/go#62408
Reviewed-on: https://go-review.googlesource.com/c/go/+/524976
Auto-Submit: Bryan Mills <bcmills@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Run-TryBot: Bryan Mills <bcmills@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Reviewed-by: Bryan Mills <bcmills@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
---
 src/sync/map.go | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

(limited to 'src/sync/map.go')

diff --git a/src/sync/map.go b/src/sync/map.go
index e8ccf58b56..00b2446153 100644
--- a/src/sync/map.go
+++ b/src/sync/map.go
@@ -461,7 +461,8 @@ func (m *Map) Range(f func(key, value any) bool) {
 		read = m.loadReadOnly()
 		if read.amended {
 			read = readOnly{m: m.dirty}
-			m.read.Store(&read)
+			copyRead := read
+			m.read.Store(&copyRead)
 			m.dirty = nil
 			m.misses = 0
 		}
-- 
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