cmd/compile: be more conservative about arm64 insns that can take zero register

It's really only needed for stores and store-like instructions
(atomic exchange, compare-and-swap, ...).

Fixes #73180

Change-Id: I8ecd833a301355adf0fa4bff43250091640c6226
Reviewed-on: https://go-review.googlesource.com/c/go/+/663155
Reviewed-by: Cherry Mui <cherryyz@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Keith Randall <khr@google.com>

1 files changed, 15 insertions, 0 deletions

diff --git a/test/fixedbugs/issue73180.go b/test/fixedbugs/issue73180.go
new file mode 100644
index 0000000000..421f42f8d6
--- /dev/null
+++ b/test/fixedbugs/issue73180.go
@@ -0,0 +1,15 @@
+// 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 p
+
+func F(a, b map[float32]int) int {
+	var st *struct {
+		n int
+		f float32
+	}
+	return a[0] + b[st.f]
+}