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php if 的实现
简单分析下php中的分支背后的实现
<?phpif($a == 1){ echo "a"; }else{ echo "b";}
1.语法分析
unticked_statement: ‘{‘ inner_statement_list ‘}‘ | T_IF parenthesis_expr { zend_do_if_cond(&$2, &$1 TSRMLS_CC); } statement { zend_do_if_after_statement(&$1, 1 TSRMLS_CC); } elseif_list else_single { zend_do_if_end(TSRMLS_C); } parenthesis_expr: ‘(‘ expr ‘)‘ { $$ = $2; } | ‘(‘ yield_expr ‘)‘ { $$ = $2; };elseif_list: /* empty */ | elseif_list T_ELSEIF parenthesis_expr { zend_do_if_cond(&$3, &$2 TSRMLS_CC); } statement { zend_do_if_after_statement(&$2, 0 TSRMLS_CC); };%token T_ELSEIF "elseif (T_ELSEIF)"else_single: /* empty */ | T_ELSE statement;%token T_ELSE "else (T_ELSE)"
对于上面的php代码来说
if 匹配 T_IF
$a == 1 匹配 parenthesis_expr , 同时语法分析器要执行 zend_do_if_cond
echo "a" 匹配 statement, 同时语法分析器要执行 zend_do_if_after_statement
else 匹配 T_ELSE, 同时语法分析器再执行zend_do_if_end
由于是先分析 $a==1, 那么它对应的opcode的opline_num 假设为1,发现if ($a == 1) 匹配BNF后,执行下面的函数,得到新的opline_num (这里为2)
,同时得到新的opline, 设置opcode为ZEND_JMPZ, 将op1设置为$a==1对应的opcode, 将op2设置为unused, 为什么呢?后来看代码才知道,
当当前分支不成立时,是要跳转的,在执行下面的函数时,还不知道要跳转的opline_num, 只有当分析完statement后,才知道这个跳转opline_num
void zend_do_if_cond(const znode *cond, znode *closing_bracket_token TSRMLS_DC) /* {{{ */{ int if_cond_op_number = get_next_op_number(CG(active_op_array)); zend_op *opline = get_next_op(CG(active_op_array) TSRMLS_CC); opline->opcode = ZEND_JMPZ; SET_NODE(opline->op1, cond); closing_bracket_token->u.op.opline_num = if_cond_op_number; SET_UNUSED(opline->op2); INC_BPC(CG(active_op_array));}
echo "a"; 这个匹配statement 就不说了,然后执行zend_do_if_after_statement,这里也要获得一个新的opline以及opline_num(这里为3),
设置opcode为ZEND_JMP, 意思为无条件跳转,同时设置opcodes的数组里第2个元素的属性op2.opline_num设置为5,为什么不是4,是因为本身的无条件跳转ZEND_JMP也算一个opcode
void zend_do_if_after_statement(const znode *closing_bracket_token, unsigned char initialize TSRMLS_DC) /* {{{ */{ int if_end_op_number = get_next_op_number(CG(active_op_array)); zend_op *opline = get_next_op(CG(active_op_array) TSRMLS_CC); zend_llist *jmp_list_ptr; opline->opcode = ZEND_JMP; /* save for backpatching */ if (initialize) { zend_llist jmp_list; zend_llist_init(&jmp_list, sizeof(int), NULL, 0); zend_stack_push(&CG(bp_stack), (void *) &jmp_list, sizeof(zend_llist)); } zend_stack_top(&CG(bp_stack), (void **) &jmp_list_ptr); zend_llist_add_element(jmp_list_ptr, &if_end_op_number); CG(active_op_array)->opcodes[closing_bracket_token->u.op.opline_num].op2.opline_num = if_end_op_number+1; SET_UNUSED(opline->op1); SET_UNUSED(opline->op2);}
else { echo "b"; } 匹配 T_ELSE statement后,马上执行 zend_do_if_end,得到新的opline_num,注意:现在的opcodes数组里有4个opcode了
第一个是$a==1对应的opcode, opline=1
第二个是ZEND_JMPZ 当 $a!=1时的opcode, opline=5
第三个是 echo "a";对应的opcode, opline =3
第四个是ZEND_JMP对应的opcode, opline=6
第五个是echo "b";对应的opcode opline=5
所以ZEND_JMP 对应的是 else {echo "b";}之后的opcode了
void zend_do_if_end(TSRMLS_D) /* {{{ */ { int next_op_number = get_next_op_number(CG(active_op_array)); zend_llist *jmp_list_ptr; zend_llist_element *le; zend_stack_top(&CG(bp_stack), (void **) &jmp_list_ptr); for (le=jmp_list_ptr->head; le; le = le->next) { CG(active_op_array)->opcodes[*((int *) le->data)].op1.opline_num = next_op_number; } zend_llist_destroy(jmp_list_ptr); zend_stack_del_top(&CG(bp_stack)); DEC_BPC(CG(active_op_array));}
pass_two函数,处理op_array中的各个opline, 上面unused掉的op2,在这里又重新赋值,就是当分支不成立时,要跳转的opcode所在的行号
ZEND_API int pass_two(zend_op_array *op_array TSRMLS_DC){ zend_op *opline, *end; if (op_array->type!=ZEND_USER_FUNCTION && op_array->type!=ZEND_EVAL_CODE) { return 0; } 。。。。 opline = op_array->opcodes; end = opline + op_array->last; while (opline < end) { if (opline->op1_type == IS_CONST) { opline->op1.zv = &op_array->literals[opline->op1.constant].constant; } if (opline->op2_type == IS_CONST) { opline->op2.zv = &op_array->literals[opline->op2.constant].constant; } switch (opline->opcode) { case ZEND_GOTO: if (Z_TYPE_P(opline->op2.zv) != IS_LONG) { zend_resolve_goto_label(op_array, opline, 1 TSRMLS_CC); } /* break omitted intentionally */ case ZEND_JMP: case ZEND_FAST_CALL: opline->op1.jmp_addr = &op_array->opcodes[opline->op1.opline_num]; break; case ZEND_JMPZ: case ZEND_JMPNZ: case ZEND_JMPZ_EX: case ZEND_JMPNZ_EX: case ZEND_JMP_SET: case ZEND_JMP_SET_VAR: opline->op2.jmp_addr = &op_array->opcodes[opline->op2.opline_num]; break; case ZEND_RETURN: case ZEND_RETURN_BY_REF: if (op_array->fn_flags & ZEND_ACC_GENERATOR) { if (opline->op1_type != IS_CONST || Z_TYPE_P(opline->op1.zv) != IS_NULL) { CG(zend_lineno) = opline->lineno; zend_error(E_COMPILE_ERROR, "Generators cannot return values using \"return\""); } opline->opcode = ZEND_GENERATOR_RETURN; } break; } ZEND_VM_SET_OPCODE_HANDLER(opline); opline++; } op_array->fn_flags |= ZEND_ACC_DONE_PASS_TWO; return 0;}
static int ZEND_FASTCALL ZEND_JMPZ_SPEC_CONST_HANDLER(ZEND_OPCODE_HANDLER_ARGS){ USE_OPLINE zval *val; int ret; SAVE_OPLINE();
//opline->op1为 if后面的表达式的值 val = opline->op1.zv; if (IS_CONST == IS_TMP_VAR && EXPECTED(Z_TYPE_P(val) == IS_BOOL)) {
ret = Z_LVAL_P(val); } else {
//判断val是否为1 true 0 false,如果为1,执行下一条opcode,如果为0,进行opcode的跳转 ret = i_zend_is_true(val); if (UNEXPECTED(EG(exception) != NULL)) { HANDLE_EXCEPTION(); } } if (!ret) {#if DEBUG_ZEND>=2 printf("Conditional jmp to %d\n", opline->op2.opline_num);#endif ZEND_VM_SET_OPCODE(opline->op2.jmp_addr); ZEND_VM_CONTINUE(); } ZEND_VM_NEXT_OPCODE();}
关于i_zend_is_true的实现
static zend_always_inline int i_zend_is_true(zval *op){ int result; switch (Z_TYPE_P(op)) { case IS_NULL: result = 0; break; case IS_LONG: case IS_BOOL: case IS_RESOURCE: result = (Z_LVAL_P(op)?1:0); break; case IS_DOUBLE: result = (Z_DVAL_P(op) ? 1 : 0); break; case IS_STRING: if (Z_STRLEN_P(op) == 0 || (Z_STRLEN_P(op)==1 && Z_STRVAL_P(op)[0]==‘0‘)) { result = 0; } else { result = 1; } break; case IS_ARRAY: result = (zend_hash_num_elements(Z_ARRVAL_P(op))?1:0); break; case IS_OBJECT: if(IS_ZEND_STD_OBJECT(*op)) { TSRMLS_FETCH(); if (Z_OBJ_HT_P(op)->cast_object) { zval tmp; if (Z_OBJ_HT_P(op)->cast_object(op, &tmp, IS_BOOL TSRMLS_CC) == SUCCESS) { result = Z_LVAL(tmp); break; } } else if (Z_OBJ_HT_P(op)->get) { zval *tmp = Z_OBJ_HT_P(op)->get(op TSRMLS_CC); if(Z_TYPE_P(tmp) != IS_OBJECT) { /* for safety - avoid loop */ convert_to_boolean(tmp); result = Z_LVAL_P(tmp); zval_ptr_dtor(&tmp); break; } } } result = 1; break; default: result = 0; break; } return result;}
php if 的实现