cmd/compile: keep call's args in elim dead auto pass

If the address of an auto is used in a Call, we need to keep it,
as we keep the Call itself.

Fixes #45693.

Change-Id: Ie548d6dffc95bf916868a8885d4ab4cf9e86355a
Reviewed-on: https://go-review.googlesource.com/c/go/+/312670
Trust: Cherry Zhang <cherryyz@google.com>
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: David Chase <drchase@google.com>

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

@@ -201,8 +201,9 @@ func elimDeadAutosGeneric(f *Func) {
 			panic("unhandled op with sym effect")
 		}
 
-		if v.Uses == 0 && v.Op != OpNilCheck || len(args) == 0 {
+		if v.Uses == 0 && v.Op != OpNilCheck && !v.Op.IsCall() && !v.Op.HasSideEffects() || len(args) == 0 {
 			// Nil check has no use, but we need to keep it.
+			// Also keep calls and values that have side effects.
 			return
 		}
 

test/fixedbugs/issue45693.go

@@ -0,0 +1,16 @@
+// compile
+
+// Copyright 2021 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.
+
+// Issue 45693: ICE with register args.
+
+package p
+
+func f() {
+	var s string
+	s = s + "" + s + "" + s + ""
+	for {
+	}
+}