cmd/compile: do not treat OpLocalAddr as load in DSE

Fixes #70409
Fixes #47107

Change-Id: I82a66c46f6b76c68e156b5d937273b0316975d44
Reviewed-on: https://go-review.googlesource.com/c/go/+/629016
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Keith Randall <[email protected]>
Reviewed-by: Keith Randall <[email protected]>
Reviewed-by: David Chase <[email protected]>

Author: fengyoulin

src/cmd/compile/internal/ssa/deadstore.go

@@ -52,9 +52,8 @@ func dse(f *Func) {
 				if v.Op == OpLocalAddr {
 					if _, ok := localAddrs[v.Aux]; !ok {
 						localAddrs[v.Aux] = v
-					} else {
-						continue
 					}
+					continue
 				}
 				if v.Op == OpInlMark {
 					// Not really a use of the memory. See #67957.

test/codegen/issue70409.go

@@ -0,0 +1,20 @@
+// asmcheck -gcflags=-d=ssa/check/on
+
+// Copyright 2024 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 codegen
+
+// amd64:-"MOVQ"
+func foo(v uint64) (b [8]byte) {
+	b[0] = byte(v)
+	b[1] = byte(v >> 8)
+	b[2] = byte(v >> 16)
+	b[3] = byte(v >> 24)
+	b[4] = byte(v >> 32)
+	b[5] = byte(v >> 40)
+	b[6] = byte(v >> 48)
+	b[7] = byte(v >> 56)
+	return b
+}