phpng-int

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phpng-int [2018/01/09 15:49]
kalle
phpng-int [2018/01/09 16:34]
kelunik fixed typos
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 New implementation assumes, that we store zval structures (not pointers) in arrays and function stack frames. It must not be a problem for arrays because scalar values are going to be just duplicated, and compound values may point to shared reference-couned structures anyway. However it is a problem for  local variables (IS_CV), because they may be referenced through stack frame (by index) and through symbol table (by name). Both must point to the same structure. Values of IS_INDIRECT types are just weak pointers to real values. When we lazily create local symbol tables, we store IS_INDIRECT values in symbol tables and initialize them with the pointers to corresponding CV slots. It means that CV access by index became extremely efficient, as we don't need to perform double or even triple dereferences as before. New implementation assumes, that we store zval structures (not pointers) in arrays and function stack frames. It must not be a problem for arrays because scalar values are going to be just duplicated, and compound values may point to shared reference-couned structures anyway. However it is a problem for  local variables (IS_CV), because they may be referenced through stack frame (by index) and through symbol table (by name). Both must point to the same structure. Values of IS_INDIRECT types are just weak pointers to real values. When we lazily create local symbol tables, we store IS_INDIRECT values in symbol tables and initialize them with the pointers to corresponding CV slots. It means that CV access by index became extremely efficient, as we don't need to perform double or even triple dereferences as before.
  
-Global symbol tales are handled a bit differently. When we enter into some user code that uses global variables, we copy them from EG(symbol_table) into CV slots and initialize symtable values with IS_INDIRECT pointers. On exit we have to restore them back.+Global symbol tables are handled a bit differently. When we enter into some user code that uses global variables, we copy them from EG(symbol_table) into CV slots and initialize symtable values with IS_INDIRECT pointers. On exit we have to restore them back.
  
 The same concept is used for object properties access. In case dynamic properties table is required it's first initialized with IS_INDIRECT references to predefined object properties slots. The same concept is used for object properties access. In case dynamic properties table is required it's first initialized with IS_INDIRECT references to predefined object properties slots.
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 ===== VM Changes ===== ===== VM Changes =====
  
-With new zval implementation IS_TMP_VAR, IS_VAR and IS_CV operands are handled in very similar way. All three operands jut refer to certain slot of the current function stack frame. Such slots are allocated on segmented VM stack together with frame header (zend_execute_data). The first slots correspond to CV variables and the following to IS_TMP_VAR and IS_VAR. Except for local and temporary variables we also allocate space for syntactically nested function calls and actual parameters, that this function may push.+With new zval implementation IS_TMP_VAR, IS_VAR and IS_CV operands are handled in very similar way. All three operands just refer to certain slot of the current function stack frame. Such slots are allocated on segmented VM stack together with frame header (zend_execute_data). The first slots correspond to CV variables and the following to IS_TMP_VAR and IS_VAR. Except for local and temporary variables we also allocate space for syntactically nested function calls and actual parameters, that this function may push.
  
 ==== Function Stack Frame (zend_execute_data) ==== ==== Function Stack Frame (zend_execute_data) ====
phpng-int.txt · Last modified: 2018/01/09 16:34 by kelunik