cmd/compile: remove check that Zero's arg has the correct base type

It doesn't have to. The type in the aux field is authoritative.
There are cases involving casting from interface{} where pointers
have a placeholder pointer type (because the type is not known when
the IData op is generated).

The check was introduced in CL 13447.

Fixes #39459

Change-Id: Id77a57577806a271aeebd20bea5d92d08ee7aa6b
Reviewed-on: https://go-review.googlesource.com/c/go/+/239817
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: David Chase <drchase@google.com>

1 files changed, 22 insertions, 0 deletions

diff --git a/test/fixedbugs/issue39459.go b/test/fixedbugs/issue39459.go
new file mode 100644
index 0000000000..de78a17ce2
--- /dev/null
+++ b/test/fixedbugs/issue39459.go
@@ -0,0 +1,22 @@
+// compile
+
+// Copyright 2020 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
+
+type T struct { // big enough to be an unSSAable type
+	a, b, c, d, e, f int
+}
+
+func f(x interface{}, p *int) {
+	_ = *p // trigger nil check here, removing it from below
+	switch x := x.(type) {
+	case *T:
+		// Zero twice, so one of them will be removed by the deadstore pass
+		*x = T{}
+		*p = 0 // store op to prevent Zero ops from being optimized by the earlier opt pass rewrite rules
+		*x = T{}
+	}
+}