[dev.ssa] cmd/compile/ssa: fix test for dse

Fix the test broken with dee1f2 by implementing Elem()

Change-Id: I7a4a487885267c24fdc52d79fb7d450231328812
Reviewed-on: https://go-review.googlesource.com/13551Reviewed-by: Keith Randall <khr@golang.org>

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

@@ -8,7 +8,8 @@ import "testing"
 
 func TestDeadStore(t *testing.T) {
 	c := testConfig(t)
-	ptrType := &TypeImpl{Size_: 8, Ptr: true, Name: "testptr"} // dummy for testing
+	elemType := &TypeImpl{Size_: 8, Name: "testtype"}
+	ptrType := &TypeImpl{Size_: 8, Ptr: true, Name: "testptr", Elem_: elemType} // dummy for testing
 	fun := Fun(c, "entry",
 		Bloc("entry",
 			Valu("start", OpArg, TypeMem, 0, ".mem"),

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

@@ -14,6 +14,7 @@ type TypeImpl struct {
 	Float   bool
 	Ptr     bool
 	string  bool
+	Elem_   Type
 
 	Name string
 }
@@ -29,7 +30,7 @@ func (t *TypeImpl) IsString() bool   { return t.string }
 func (t *TypeImpl) IsMemory() bool   { return false }
 func (t *TypeImpl) IsFlags() bool    { return false }
 func (t *TypeImpl) String() string   { return t.Name }
-func (t *TypeImpl) Elem() Type       { panic("not implemented") }
+func (t *TypeImpl) Elem() Type       { return t.Elem_ }
 func (t *TypeImpl) PtrTo() Type      { panic("not implemented") }
 
 func (t *TypeImpl) Equal(u Type) bool {