cmd/compile: fix unsafeValue handles OLSH/ORSH wrong

For OLSH/ORSH, the right node is not a uintptr-typed. However,
unsafeValue still be called recursively for it, causing the
compiler crashes.

To fixing, the right node only needs to be evaluated
for side-effects, so just discard its value.

Fixes #32959

Change-Id: I34d5aa0823a0545f6dad1ec34774235ecf11addc
Reviewed-on: https://go-review.googlesource.com/c/go/+/185039
Run-TryBot: Cuong Manh Le <cuong.manhle.vn@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: David Chase <drchase@google.com>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

src/cmd/compile/internal/gc/escape.go

@@ -614,9 +614,14 @@ func (e *Escape) unsafeValue(k EscHole, n *Node) {
 		}
 	case OPLUS, ONEG, OBITNOT:
 		e.unsafeValue(k, n.Left)
-	case OADD, OSUB, OOR, OXOR, OMUL, ODIV, OMOD, OLSH, ORSH, OAND, OANDNOT:
+	case OADD, OSUB, OOR, OXOR, OMUL, ODIV, OMOD, OAND, OANDNOT:
 		e.unsafeValue(k, n.Left)
 		e.unsafeValue(k, n.Right)
+	case OLSH, ORSH:
+		e.unsafeValue(k, n.Left)
+		// RHS need not be uintptr-typed (#32959) and can't meaningfully
+		// flow pointers anyway.
+		e.discard(n.Right)
 	default:
 		e.exprSkipInit(e.discardHole(), n)
 	}

test/fixedbugs/issue32959.go

+// 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.
+
+// Test escape analysis with shifting constant
+
+package main
+
+import "unsafe"
+
+func main() {
+	var l uint64
+	var p unsafe.Pointer
+	_ = unsafe.Pointer(uintptr(p) + (uintptr(l) >> 1))
+}