diff --git a/src/cmd/compile/internal/ssa/compile.go b/src/cmd/compile/internal/ssa/compile.go
index f061b624483..1a0a46c154c 100644
--- a/src/cmd/compile/internal/ssa/compile.go
+++ b/src/cmd/compile/internal/ssa/compile.go
@@ -409,6 +409,7 @@ var passes = [...]pass{
 	{name: "opt deadcode", fn: deadcode, required: true}, // remove any blocks orphaned during opt
 	{name: "generic cse", fn: cse},
 	{name: "phiopt", fn: phiopt},
+	{name: "gcse deadcode", fn: deadcode, required: true}, // clean out after cse and phiopt
 	{name: "nilcheckelim", fn: nilcheckelim},
 	{name: "prove", fn: prove},
 	{name: "fuse plain", fn: fusePlain},
diff --git a/test/prove.go b/test/prove.go
index 6629982ba85..00fc94e7219 100644
--- a/test/prove.go
+++ b/test/prove.go
@@ -507,7 +507,7 @@ func sm1(b []int, x int) {
 	useSlice(b[2:8]) // ERROR "Proved slicemask not needed$"
 	// Test non-constant argument with known limits.
 	if cap(b) > 10 {
-		useSlice(b[2:]) // ERROR "Proved slicemask not needed$"
+		useSlice(b[2:])
 	}
 }