struct _zend_op 
{
opcode_handler_t handler; // 执行该opcode时调用的处理函数
znode_op op1; // opcode所操作的操作数
znode_op op2; // opcode所操作的操作数
znode_op result;
ulong extended_value;
uint lineno;
zend_uchar opcode; // opcode代码
zend_uchar op1_type;
zend_uchar op2_type;
zend_uchar result_type;
}; 

void zend_do_print(znode *result, const znode *arg TSRMLS_DC) /* {{{ */
{ 
//新创建一条zend_op 
zend_op *opline = get_next_op(CG(active_op_array) TSRMLS_CC);

//将新建的zend_op的返回值类型设置为临时变量(IS_TMP_VAR)，因为print中的内存仅仅为了临时输出，并不需要保存
opline->result_type = IS_TMP_VAR;
//为临时变量申请空间
opline->result.var = get_temporary_variable(CG(active_op_array));
//指定opcode为ZEND_PRINT
opline->opcode = ZEND_PRINT;
//将传递进来的参数赋值给这条opcode的第一个操作数
SET_NODE(opline->op1, arg);
SET_UNUSED(opline->op2);
GET_NODE(result, opline->result);
}

#define ZEND_NOP 0
#define ZEND_ADD 1
#define ZEND_SUB 2
#define ZEND_MUL 3
#define ZEND_DIV 4
#define ZEND_MOD 5
#define ZEND_SL 6
#define ZEND_SR 7
#define ZEND_CONCAT 8
#define ZEND_BW_OR 9
#define ZEND_BW_AND 10
#define ZEND_BW_XOR 11
#define ZEND_BW_NOT 12
#define ZEND_BOOL_NOT 13
#define ZEND_BOOL_XOR 14
#define ZEND_IS_IDENTICAL 15
#define ZEND_IS_NOT_IDENTICAL 16
#define ZEND_IS_EQUAL 17
#define ZEND_IS_NOT_EQUAL 18
#define ZEND_IS_SMALLER 19
#define ZEND_IS_SMALLER_OR_EQUAL 20
#define ZEND_CAST 21
#define ZEND_QM_ASSIGN 22
#define ZEND_ASSIGN_ADD 23
#define ZEND_ASSIGN_SUB 24
#define ZEND_ASSIGN_MUL 25
#define ZEND_ASSIGN_DIV 26
#define ZEND_ASSIGN_MOD 27
#define ZEND_ASSIGN_SL 28
#define ZEND_ASSIGN_SR 29
#define ZEND_ASSIGN_CONCAT 30
#define ZEND_ASSIGN_BW_OR 31
#define ZEND_ASSIGN_BW_AND 32
#define ZEND_ASSIGN_BW_XOR 33
#define ZEND_PRE_INC 34
#define ZEND_PRE_DEC 35
#define ZEND_POST_INC 36
#define ZEND_POST_DEC 37
#define ZEND_ASSIGN 38
#define ZEND_ASSIGN_REF 39
#define ZEND_ECHO 40
#define ZEND_PRINT 41
#define ZEND_JMP 42
#define ZEND_JMPZ 43
#define ZEND_JMPNZ 44
#define ZEND_JMPZNZ 45
#define ZEND_JMPZ_EX 46
#define ZEND_JMPNZ_EX 47
#define ZEND_CASE 48
#define ZEND_SWITCH_FREE 49
#define ZEND_BRK 50
#define ZEND_CONT 51
#define ZEND_BOOL 52
#define ZEND_INIT_STRING 53
#define ZEND_ADD_CHAR 54
#define ZEND_ADD_STRING 55
#define ZEND_ADD_VAR 56
#define ZEND_BEGIN_SILENCE 57
#define ZEND_END_SILENCE 58
#define ZEND_INIT_FCALL_BY_NAME 59
#define ZEND_DO_FCALL 60
#define ZEND_DO_FCALL_BY_NAME 61
#define ZEND_RETURN 62
#define ZEND_RECV 63
#define ZEND_RECV_INIT 64
#define ZEND_SEND_VAL 65
#define ZEND_SEND_VAR 66
#define ZEND_SEND_REF 67
#define ZEND_NEW 68
#define ZEND_INIT_NS_FCALL_BY_NAME 69
#define ZEND_FREE 70
#define ZEND_INIT_ARRAY 71
#define ZEND_ADD_ARRAY_ELEMENT 72
#define ZEND_INCLUDE_OR_EVAL 73
#define ZEND_UNSET_VAR 74
#define ZEND_UNSET_DIM 75
#define ZEND_UNSET_OBJ 76
#define ZEND_FE_RESET 77
#define ZEND_FE_FETCH 78
#define ZEND_EXIT 79
#define ZEND_FETCH_R 80
#define ZEND_FETCH_DIM_R 81
#define ZEND_FETCH_OBJ_R 82
#define ZEND_FETCH_W 83
#define ZEND_FETCH_DIM_W 84
#define ZEND_FETCH_OBJ_W 85
#define ZEND_FETCH_RW 86
#define ZEND_FETCH_DIM_RW 87
#define ZEND_FETCH_OBJ_RW 88
#define ZEND_FETCH_IS 89
#define ZEND_FETCH_DIM_IS 90
#define ZEND_FETCH_OBJ_IS 91
#define ZEND_FETCH_FUNC_ARG 92
#define ZEND_FETCH_DIM_FUNC_ARG 93
#define ZEND_FETCH_OBJ_FUNC_ARG 94
#define ZEND_FETCH_UNSET 95
#define ZEND_FETCH_DIM_UNSET 96
#define ZEND_FETCH_OBJ_UNSET 97
#define ZEND_FETCH_DIM_TMP_VAR 98
#define ZEND_FETCH_CONSTANT 99
#define ZEND_GOTO 100
#define ZEND_EXT_STMT 101
#define ZEND_EXT_FCALL_BEGIN 102
#define ZEND_EXT_FCALL_END 103
#define ZEND_EXT_NOP 104
#define ZEND_TICKS 105
#define ZEND_SEND_VAR_NO_REF 106
#define ZEND_CATCH 107
#define ZEND_THROW 108
#define ZEND_FETCH_CLASS 109
#define ZEND_CLONE 110
#define ZEND_RETURN_BY_REF 111
#define ZEND_INIT_METHOD_CALL 112
#define ZEND_INIT_STATIC_METHOD_CALL 113
#define ZEND_ISSET_ISEMPTY_VAR 114
#define ZEND_ISSET_ISEMPTY_DIM_OBJ 115
#define ZEND_PRE_INC_OBJ 132
#define ZEND_PRE_DEC_OBJ 133
#define ZEND_POST_INC_OBJ 134
#define ZEND_POST_DEC_OBJ 135
#define ZEND_ASSIGN_OBJ 136
#define ZEND_INSTANCEOF 138
#define ZEND_DECLARE_CLASS 139
#define ZEND_DECLARE_INHERITED_CLASS 140
#define ZEND_DECLARE_FUNCTION 141
#define ZEND_RAISE_ABSTRACT_ERROR 142
#define ZEND_DECLARE_CONST 143
#define ZEND_ADD_INTERFACE 144
#define ZEND_DECLARE_INHERITED_CLASS_DELAYED 145
#define ZEND_VERIFY_ABSTRACT_CLASS 146
#define ZEND_ASSIGN_DIM 147
#define ZEND_ISSET_ISEMPTY_PROP_OBJ 148
#define ZEND_HANDLE_EXCEPTION 149
#define ZEND_USER_OPCODE 150
#define ZEND_JMP_SET 152
#define ZEND_DECLARE_LAMBDA_FUNCTION 153
#define ZEND_ADD_TRAIT 154
#define ZEND_BIND_TRAITS 155
#define ZEND_SEPARATE 156
#define ZEND_QM_ASSIGN_VAR 157
#define ZEND_JMP_SET_VAR 158
#define ZEND_DISCARD_EXCEPTION 159
#define ZEND_YIELD 160
#define ZEND_GENERATOR_RETURN 161
#define ZEND_FAST_CALL 162
#define ZEND_FAST_RET 163
#define ZEND_RECV_VARIADIC 164
#define ZEND_SEND_UNPACK 165
#define ZEND_POW 166
#define ZEND_ASSIGN_POW 167 

void zend_init_opcodes_handlers(void)
{
static const opcode_handler_t labels[] = {
..
ZEND_ASSIGN_SPEC_CV_CONST_HANDLER,
..
}
}

typedef struct _znode { /* used only during compilation */
/*
这个int类型的字段定义znode操作数的类型
#define IS_CONST (1<<0) //表示常量，例如$a = 123; $b = "hello";这些代码生成OP后，123和"hello"都是以常量类型操作数存在
#define IS_TMP_VAR (1<<1) //表示临时变量，临时变量一般在前面加~来表示，这是一些OP执行过程中需要用到的中间变量，例如初始化一个数组的时候，就需要一个临时变量来暂时存储数组zval，然后将数组赋值给变量
#define IS_VAR (1<<2) //一般意义上的变量，以$开发表示
#define IS_UNUSED (1<<3) // Unused variable 
#define IS_CV (1<<4) // Compiled variable，这种类型的操作数比较重要，此类型是在PHP后来的版本中(大概5.1)中才出现，CV的意思是compiled variable，即编译后的变量，变量都是保存在一个符号表中，这个符号表是一个哈希表，如果每次读写变量的时候都需要到哈希表中去检索，会对效率有一定的影响，因此在执行上下文环境中，会将一些编译期间生成的变量缓存起来。此类型操作数一般以!开头表示，比如变量$a=123;$b="hello"这段代码，$a和$b对应的操作数可能就是!0和!1, 0和1相当于一个索引号，通过索引号从缓存中取得相应的值
*/
int op_type;
/*
此字段为一个联合体，根据op_type的不同，u取不同的值
1. op_type=IS_CONST的时候，u中的constant保存的就是操作数对应的zval结构
2. 例如$a=123时，123这个操作数中，u中的constant是一个IS_LONG类型的zval,其值lval为123 
*/
union {
znode_op op;
zval constant; /* replaced by literal/zv */
zend_op_array *op_array;
zend_ast *ast;
} u;
zend_uint EA; /* extended attributes */
} znode; 

zend_op *opline = get_next_op(CG(active_op_array) TSRMLS_CC); 

struct _zend_op_array 
{
/* Common elements */
zend_uchar type;
const char *function_name; // 如果是用户定义的函数则，这里将保存函数的名字
zend_class_entry *scope;
zend_uint fn_flags;
union _zend_function *prototype;
zend_uint num_args;
zend_uint required_num_args;
zend_arg_info *arg_info;
/* END of common elements */
zend_uint *refcount;
zend_op *opcodes; // opcode数组
zend_uint last;
zend_compiled_variable *vars;
int last_var;
zend_uint T;
zend_uint nested_calls;
zend_uint used_stack;
zend_brk_cont_element *brk_cont_array;
int last_brk_cont;
zend_try_catch_element *try_catch_array;
int last_try_catch;
zend_bool has_finally_block;
/* static variables support */
HashTable *static_variables;
zend_uint this_var;
const char *filename;
zend_uint line_start;
zend_uint line_end;
const char *doc_comment;
zend_uint doc_comment_len;
zend_uint early_binding; /* the linked list of delayed declarations */
zend_literal *literals;
int last_literal;
void **run_time_cache;
int last_cache_slot;
void *reserved[ZEND_MAX_RESERVED_RESOURCES];
}; 

ZEND_API void execute(zend_op_array *op_array TSRMLS_DC)
{
// ... 循环执行op_array中的opcode或者执行其他op_array中的opcode
}

http://www.nowamagic.net/librarys/veda/detail/1325
http://php.net/manual/zh/internals2.opcodes.list.php
http://www.nowamagic.net/librarys/veda/detail/1543
http://www.nowamagic.net/librarys/veda/detail/1324
http://www.nowamagic.net/librarys/veda/detail/1543 
http://www.laruence.com/2008/06/18/221.html
http://www.php-internals.com/book/?p=chapt02/02-03-02-opcode 

http://www.php-internals.com/book/?p=chapt02/02-03-03-from-opcode-to-handler