cmd/compile: fix crash when memmove argument is not the right type

Make sure the argument to memmove is of pointer type before we try to
get the element type.

This has been noticed for code that uses unsafe+linkname so it can
call runtime.memmove. Probably not the best thing to allow, but the
code is out there and we'd rather not break it unnecessarily.

Fixes #30061

Change-Id: I334a8453f2e293959fd742044c43fbe93f0b3d31
Reviewed-on: https://go-review.googlesource.com/c/160826
Run-TryBot: Keith Randall <[email protected]>
Reviewed-by: Ian Lance Taylor <[email protected]>
TryBot-Result: Gobot Gobot <[email protected]>

Author: randall77

src/cmd/compile/internal/ssa/gen/generic.rules

@@ -1354,6 +1354,7 @@
 // Inline small or disjoint runtime.memmove calls with constant length.
 (StaticCall {sym} s1:(Store _ (Const(64|32) [sz]) s2:(Store  _ src s3:(Store {t} _ dst mem))))
 	&& isSameSym(sym,"runtime.memmove")
+	&& t.(*types.Type).IsPtr() // avoids TUINTPTR, see issue 30061
 	&& s1.Uses == 1 && s2.Uses == 1 && s3.Uses == 1
 	&& isInlinableMemmove(dst,src,sz,config)
 	&& clobber(s1) && clobber(s2) && clobber(s3)

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

@@ -0,0 +1,20 @@
+// compile
+
+// Copyright 2019 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.
+
+// Make sure we can linkname to memmove with an unsafe.Pointer argument.
+
+package p
+
+import "unsafe"
+
+//go:linkname memmove runtime.memmove
+func memmove(to, from unsafe.Pointer, n uintptr)
+
+var V1, V2 int
+
+func F() {
+	memmove(unsafe.Pointer(&V1), unsafe.Pointer(&V2), unsafe.Sizeof(int(0)))
+}