What optimizations have been done in php7?

1 zval uses stack memory

In Zend engine and extensions, it is often necessary to create a PHP variable, and the bottom layer is a zval pointer. Previous versions used MAKE_STD_ZVAL to dynamically allocate a zval memory from the heap. (Recommended learning: PHP video tutorial)

And PHP7 can use stack memory directly. Variables created in PHP code have also been optimized, PHP7 pre-allocates zval directly on the stack memory. This saves a lot of memory allocation and memory management operations.

Second zend_string stores hash values, and array queries no longer need to repeatedly calculate hash

PHP7 creates a new type for strings called zend_string, in addition to char * pointers and lengths In addition, a hash field is added to save the hash value of the string.

Array is the core data structure in PHP. There are often a large number of $array[$key] operations in PHP programs. Although the time complexity of hashtable search is O(1), $key must be converted into hash. The value must be calculated.

Not just array operations, in fact, the bottom layer of PHP must first find the corresponding pointer through the hashtable when accessing class attributes, class methods, and functions, and then perform the corresponding operation. Before PHP7, the Zend engine used a lot of CPU time to calculate hash values.

In fact, after the PHP program is run, the value of $key remains unchanged in most cases. PHP7 simply saves the hash value and uses it directly next time, thus saving a lot of hash calculation operations. The performance of PHP's hashtable is consistent with that of C arrays.

Store data directly in three hashtable buckets

Each element of PHP5’s hashtable is a Bucket*, while PHP7 stores Bucket directly, reducing the number of memory applications and improving Cache hit rate and memory access speed.

Four zend_parse_parameters is changed to macro implementation

When inputting parameters between PHP’s C extension function and variables in PHP, use the zend_parse_parameters() function. This function is based on a The string parameter finds the zval pointer corresponding to PHP and then assigns it. This function actually has a certain performance cost.

PHP7 directly uses macros to replace the zend_parse_parameters function. In C extensions, it is no longer necessary to use zend_parse_parameters to search parameters one by one. Parameter assignment will be automatically implemented after macro expansion. This alone improves performance by 5%.

5 4 new OPCODEs

Many PHP programs will use a lot of call_user_function, is_int/string/array, strlen, defined functions. PHP5 is provided in the form of extension functions. These four types of functions in PHP7 are changed to ZendVM's OPCODE instructions, which execute faster.

6 Other more optimizations

In addition to the above five main optimization points, PHP7 has other more detailed performance optimizations.

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