// offset translates a token position into a 0-indexed byte offset.
func (f *File) offset(pos token.Pos) int {
	return f.fset.Position(pos).Offset
}

// addVariables adds to the end of the file the declarations to set up the counter and position variables.
func (f *File) addVariables(w io.Writer) {
	if *pkgcfg != "" {
		return
	}
	// Self-check: Verify that the instrumented basic blocks are disjoint.
	t := make([]block1, len(f.blocks))