func (f *File) saveExprs(x interface{}, context astContext) {
	switch x := x.(type) {
	case *ast.Expr:
		switch (*x).(type) {
		case *ast.SelectorExpr:
			f.saveRef(x, context)
		}
	case *ast.CallExpr:
		f.saveCall(x, context)
	}
}

// Save references to C.xxx for later processing.
func (f *File) saveRef(n *ast.Expr, context astContext) {
	sel := (*n).(*ast.SelectorExpr)

pkg go/types, type Info struct, Selections map[*ast.SelectorExpr]*Selection
pkg go/types, type Info struct, Types map[ast.Expr]TypeAndValue
pkg go/types, type Info struct, Uses map[*ast.Ident]Object
pkg go/types, type Initializer struct
pkg go/types, type Initializer struct, Lhs []*Var
pkg go/types, type Initializer struct, Rhs ast.Expr
pkg go/types, type Interface struct
pkg go/types, type Label struct
pkg go/types, type Map struct

// see in assembly code are simple, but for the record:
//
// 1) Evaluation uses uint64; the old one used int64.
// 2) Precedence uses Go rules not C rules.

// expr = term | term ('+' | '-' | '|' | '^') term.
func (p *Parser) expr() uint64 {
	value := p.term()
	for {
		switch p.peek() {
		case '+':
			p.next()
			value += p.term()
		case '-':
			p.next()
			value -= p.term()

pkg go/ast, type FuncType struct, TypeParams *FieldList
pkg go/ast, type IndexListExpr struct
pkg go/ast, type IndexListExpr struct, Indices []Expr
pkg go/ast, type IndexListExpr struct, Lbrack token.Pos
pkg go/ast, type IndexListExpr struct, Rbrack token.Pos
pkg go/ast, type IndexListExpr struct, X Expr
pkg go/ast, type TypeSpec struct, TypeParams *FieldList
pkg go/constant, method (Kind) String() string
pkg go/token, const TILDE = 88

	EORW R12->27, R10, R19                     // 536d8c4a
	EOR R2<<59, R30, R17                       // d1ef02ca
	ERET                                       // e0039fd6
	EXTRW $7, R8, R10, R25                     // 591d8813
	EXTR $35, R22, R12, R8                     // 888dd693
	SEVL                                       // bf2003d5
	HINT $6                                    // df2003d5
	HINT $0                                    // 1f2003d5

pkg go/ast, type Importer //deprecated #52463
pkg go/ast, type Object //deprecated #52463
pkg go/ast, type Package //deprecated #52463
pkg go/ast, type Scope //deprecated #52463
pkg go/build/constraint, func GoVersion(Expr) string #59033
pkg go/build, type Directive struct #56986
pkg go/build, type Directive struct, Pos token.Position #56986
pkg go/build, type Directive struct, Text string #56986