[dev.ssa] cmd/compile: handle OLITERAL nil expressions

Change-Id: I02b8fb277b486eaf0916ddcd8f28c062d4022d4b
Reviewed-on: https://go-review.googlesource.com/12150
Reviewed-by: Keith Randall <khr@golang.org>
diff --git a/src/cmd/compile/internal/gc/ssa.go b/src/cmd/compile/internal/gc/ssa.go
index 589257b..b016bb1 100644
--- a/src/cmd/compile/internal/gc/ssa.go
+++ b/src/cmd/compile/internal/gc/ssa.go
@@ -480,6 +480,8 @@
 			return s.constInt(n.Type, Mpgetfix(n.Val().U.(*Mpint)))
 		case CTSTR, CTBOOL:
 			return s.entryNewValue0A(ssa.OpConst, n.Type, n.Val().U)
+		case CTNIL:
+			return s.entryNewValue0(ssa.OpConst, n.Type)
 		default:
 			s.Unimplementedf("unhandled OLITERAL %v", n.Val().Ctype())
 			return nil