func checkVarValue(t *testing.T, prog *ssa.Program, pkg *ssa.Package, ref []ast.Node, obj *types.Var, expKind string, wantAddr bool) {
	// The prefix of all assertions messages.
	prefix := fmt.Sprintf("VarValue(%s @ L%d)",
		obj, prog.Fset.Position(ref[0].Pos()).Line)

	v := prog.VarValue(obj, pkg, ref)

	// Kind is the concrete type of the ssa Value.
	gotKind := "nil"
	if v != nil {
		gotKind = fmt.Sprintf("%T", v)[len("*ssa."):]
	}

	// fmt.Printf("%s = %v (kind %q; expect %q) addr=%t\n", prefix, v, gotKind, expKind, wantAddr) // debugging

	// Check the kinds match.
	// "nil" indicates expected failure (e.g. optimized away).
	if expKind != gotKind {
		t.Errorf("%s concrete type == %s, want %s", prefix, gotKind, expKind)
	}

	// Check the types match.
	// If wantAddr, the expected type is the object's address.
	if v != nil {
		expType := obj.Type()
		if wantAddr {
			expType = types.NewPointer(expType)
		}
		if !types.IsIdentical(v.Type(), expType) {
			t.Errorf("%s.Type() == %s, want %s", prefix, v.Type(), expType)
		}
	}
}

// ssaValueForExpr returns the ssa.Value of the non-ast.Ident
// expression whose path to the root of the AST is path.  It may
// return a nil Value without an error to indicate the pointer
// analysis is not appropriate.
//
func ssaValueForExpr(prog *ssa.Program, qinfo *importer.PackageInfo, path []ast.Node) (ssa.Value, error) {
	pkg := prog.Package(qinfo.Pkg)
	pkg.SetDebugMode(true)
	pkg.Build()

	fn := ssa.EnclosingFunction(pkg, path)
	if fn == nil {
		return nil, fmt.Errorf("no SSA function built for this location (dead code?)")
	}

	if v := fn.ValueForExpr(path[0].(ast.Expr)); v != nil {
		return v, nil
	}

	return nil, fmt.Errorf("can't locate SSA Value for expression in %s", fn)
}

func checkFuncValue(t *testing.T, prog *ssa.Program, obj *types.Func) {
	fn := prog.FuncValue(obj)
	// fmt.Printf("FuncValue(%s) = %s\n", obj, fn) // debugging
	if fn == nil {
		t.Errorf("FuncValue(%s) == nil", obj)
		return
	}
	if fnobj := fn.Object(); fnobj != obj {
		t.Errorf("FuncValue(%s).Object() == %s; value was %s",
			obj, fnobj, fn.Name())
		return
	}
	if !types.IsIdentical(fn.Type(), obj.Type()) {
		t.Errorf("FuncValue(%s).Type() == %s", obj, fn.Type())
		return
	}
}

// ssaValueForIdent returns the ssa.Value for the ast.Ident whose path
// to the root of the AST is path.  It may return a nil Value without
// an error to indicate the pointer analysis is not appropriate.
//
func ssaValueForIdent(prog *ssa.Program, qinfo *importer.PackageInfo, obj types.Object, path []ast.Node) (ssa.Value, error) {
	if obj, ok := obj.(*types.Var); ok {
		pkg := prog.Package(qinfo.Pkg)
		pkg.Build()
		if v := prog.VarValue(obj, pkg, path); v != nil {
			// Don't run pointer analysis on a ref to a const expression.
			if _, ok := v.(*ssa.Const); ok {
				v = nil
			}
			return v, nil
		}
		return nil, fmt.Errorf("can't locate SSA Value for var %s", obj.Name())
	}

	// Don't run pointer analysis on const/func objects.
	return nil, nil
}

func checkConstValue(t *testing.T, prog *ssa.Program, obj *types.Const) {
	c := prog.ConstValue(obj)
	// fmt.Printf("ConstValue(%s) = %s\n", obj, c) // debugging
	if c == nil {
		t.Errorf("ConstValue(%s) == nil", obj)
		return
	}
	if !types.IsIdentical(c.Type(), obj.Type()) {
		t.Errorf("ConstValue(%s).Type() == %s", obj, c.Type())
		return
	}
	if obj.Name() != "nil" {
		if !exact.Compare(c.Value, token.EQL, obj.Val()) {
			t.Errorf("ConstValue(%s).Value (%s) != %s",
				obj, c.Value, obj.Val())
			return
		}
	}
}

// ssaValueForIdent returns the ssa.Value for the ast.Ident whose path
// to the root of the AST is path.  isAddr reports whether the
// ssa.Value is the address denoted by the ast.Ident, not its value.
//
func ssaValueForIdent(prog *ssa.Program, qinfo *importer.PackageInfo, obj types.Object, path []ast.Node) (value ssa.Value, isAddr bool, err error) {
	switch obj := obj.(type) {
	case *types.Var:
		pkg := prog.Package(qinfo.Pkg)
		pkg.Build()
		if v, addr := prog.VarValue(obj, pkg, path); v != nil {
			return v, addr, nil
		}
		return nil, false, fmt.Errorf("can't locate SSA Value for var %s", obj.Name())

	case *types.Func:
		return prog.FuncValue(obj), false, nil
	}
	panic(obj)
}