Shrink some commonly used structs by reordering members (#10880)

Struct members require some alignment based on their type. This means
that if a struct member is not aligned, there will be a hole created by
the compiler in the struct, which is wasted space. This patch reorders
some of the most commonly used structs, but in such a way that the
fields which were in the same cache line still belong together.
The only exception to this is exception_ignore_args, which was
temporally not close to nearby members, and as such I placed
it further up to close a hole.

On 64-bit Linux this gives us the following shrinks:
* zend_op_array: 248 -> 240
* zend_ssa_var: 56 -> 48
* zend_ssa_var_info: 48 -> 40
* php_core_globals: 672 -> 608
* zend_executor_globals: 1824 -> 1792

On 32-bit, the sizes will either remain the same or will result in
smaller shrinks.

Author: ndossche

UPGRADING.INTERNALS

@@ -39,6 +39,9 @@ PHP 8.3 INTERNALS UPGRADE NOTES
   - zend_fiber_init_context()
 * The fast_add_function() has been removed, use add_function() that will
   call the static inline add_function_fast() instead.
+* The order of members of zend_op_array, zend_ssa_var, zend_ssa_var_info,
+  zend_executor_globals and php_core_globals have changed to improve
+  struct packing which reduces their size.
 
 ========================
 2. Build system changes

Zend/Optimizer/zend_ssa.h

@@ -110,8 +110,8 @@ typedef struct _zend_ssa_var {
 	int                    var;            /* original var number; op.var for CVs and following numbers for VARs and TMP_VARs */
 	int                    scc;            /* strongly connected component */
 	int                    definition;     /* opcode that defines this value */
-	zend_ssa_phi          *definition_phi; /* phi that defines this value */
 	int                    use_chain;      /* uses of this value, linked through opN_use_chain */
+	zend_ssa_phi          *definition_phi; /* phi that defines this value */
 	zend_ssa_phi          *phi_use_chain;  /* uses of this value in Phi, linked through use_chain */
 	zend_ssa_phi          *sym_use_chain;  /* uses of this value in Pi constraints */
 	unsigned int           no_val : 1;     /* value doesn't matter (used as op1 in ZEND_ASSIGN) */
@@ -122,16 +122,16 @@ typedef struct _zend_ssa_var {
 
 typedef struct _zend_ssa_var_info {
 	uint32_t               type; /* inferred type (see zend_inference.h) */
+	bool                   has_range : 1;
+	bool                   is_instanceof : 1; /* 0 - class == "ce", 1 - may be child of "ce" */
+	bool                   recursive : 1;
+	bool                   use_as_double : 1;
+	bool                   delayed_fetch_this : 1;
+	bool                   avoid_refcounting : 1;
+	bool                   guarded_reference : 1;
+	bool                   indirect_reference : 1; /* IS_INDIRECT returned by FETCH_DIM_W/FETCH_OBJ_W */
 	zend_ssa_range         range;
 	zend_class_entry      *ce;
-	unsigned int           has_range : 1;
-	unsigned int           is_instanceof : 1; /* 0 - class == "ce", 1 - may be child of "ce" */
-	unsigned int           recursive : 1;
-	unsigned int           use_as_double : 1;
-	unsigned int           delayed_fetch_this : 1;
-	unsigned int           avoid_refcounting : 1;
-	unsigned int           guarded_reference : 1;
-	unsigned int           indirect_reference : 1; /* IS_INDIRECT returned by FETCH_DIM_W/FETCH_OBJ_W */
 } zend_ssa_var_info;
 
 typedef struct _zend_ssa {

Zend/zend_compile.h

@@ -448,8 +448,8 @@ struct _zend_op_array {
 	uint32_t required_num_args;
 	zend_arg_info *arg_info;
 	HashTable *attributes;
-	uint32_t T;         /* number of temporary variables */
 	ZEND_MAP_PTR_DEF(void **, run_time_cache);
+	uint32_t T;         /* number of temporary variables */
 	/* END of common elements */
 
 	int cache_size;     /* number of run_time_cache_slots * sizeof(void*) */
@@ -503,8 +503,8 @@ typedef struct _zend_internal_function {
 	uint32_t required_num_args;
 	zend_internal_arg_info *arg_info;
 	HashTable *attributes;
-	uint32_t T;         /* number of temporary variables */
 	ZEND_MAP_PTR_DEF(void **, run_time_cache);
+	uint32_t T;         /* number of temporary variables */
 	/* END of common elements */
 
 	zif_handler handler;
@@ -529,8 +529,8 @@ union _zend_function {
 		uint32_t required_num_args;
 		zend_arg_info *arg_info;  /* index -1 represents the return value info, if any */
 		HashTable   *attributes;
-		uint32_t T;         /* number of temporary variables */
 		ZEND_MAP_PTR_DEF(void **, run_time_cache);
+		uint32_t T;         /* number of temporary variables */
 	} common;
 
 	zend_op_array op_array;

Zend/zend_execute.c

@@ -145,8 +145,8 @@ ZEND_API const zend_internal_function zend_pass_function = {
 	0,                      /* required_num_args */
 	(zend_internal_arg_info *) zend_pass_function_arg_info + 1, /* arg_info */
 	NULL,                   /* attributes        */
-	0,                      /* T                 */
 	NULL,                   /* run_time_cache    */
+	0,                      /* T                 */
 	ZEND_FN(pass),          /* handler           */
 	NULL,                   /* module            */
 	{NULL,NULL,NULL,NULL}   /* reserved          */

Zend/zend_globals.h

@@ -193,22 +193,24 @@ struct _zend_executor_globals {
 
 	uint32_t jit_trace_num; /* Used by tracing JIT to reference the currently running trace */
 
-	zend_long precision;
-
 	int ticks_count;
 
+	zend_long precision;
+
 	uint32_t persistent_constants_count;
 	uint32_t persistent_functions_count;
 	uint32_t persistent_classes_count;
 
-	HashTable *in_autoload;
-	bool full_tables_cleanup;
-
 	/* for extended information support */
 	bool no_extensions;
 
+	bool full_tables_cleanup;
+
 	zend_atomic_bool vm_interrupt;
 	zend_atomic_bool timed_out;
+
+	HashTable *in_autoload;
+
 	zend_long hard_timeout;
 	void *stack_base;
 	void *stack_limit;
@@ -221,20 +223,21 @@ struct _zend_executor_globals {
 	HashTable persistent_list;
 
 	int user_error_handler_error_reporting;
+	bool exception_ignore_args;
 	zval user_error_handler;
 	zval user_exception_handler;
 	zend_stack user_error_handlers_error_reporting;
 	zend_stack user_error_handlers;
 	zend_stack user_exception_handlers;
 
-	zend_error_handling_t  error_handling;
 	zend_class_entry      *exception_class;
+	zend_error_handling_t  error_handling;
+
+	int capture_warnings_during_sccp;
 
 	/* timeout support */
 	zend_long timeout_seconds;
 
-	int capture_warnings_during_sccp;
-
 	HashTable *ini_directives;
 	HashTable *modified_ini_directives;
 	zend_ini_entry *error_reporting_ini_entry;
@@ -266,7 +269,6 @@ struct _zend_executor_globals {
 
 	HashTable weakrefs;
 
-	bool exception_ignore_args;
 	zend_long exception_string_param_max_len;
 
 	zend_get_gc_buffer get_gc_buffer;

main/php_globals.h

@@ -53,12 +53,19 @@ typedef struct _arg_separators {
 } arg_separators;
 
 struct _php_core_globals {
-	bool implicit_flush;
-
 	zend_long output_buffering;
 
+	bool implicit_flush;
+
 	bool enable_dl;
 
+	uint8_t display_errors;
+	bool display_startup_errors;
+	bool log_errors;
+	bool ignore_repeated_errors;
+	bool ignore_repeated_source;
+	bool report_memleaks;
+
 	char *output_handler;
 
 	char *unserialize_callback_func;
@@ -67,12 +74,6 @@ struct _php_core_globals {
 	zend_long memory_limit;
 	zend_long max_input_time;
 
-	uint8_t display_errors;
-	bool display_startup_errors;
-	bool log_errors;
-	bool ignore_repeated_errors;
-	bool ignore_repeated_source;
-	bool report_memleaks;
 	char *error_log;
 
 	char *doc_root;
@@ -116,12 +117,12 @@ struct _php_core_globals {
 	bool register_argc_argv;
 	bool auto_globals_jit;
 
-	char *docref_root;
-	char *docref_ext;
-
 	bool html_errors;
 	bool xmlrpc_errors;
 
+	char *docref_root;
+	char *docref_ext;
+
 	zend_long xmlrpc_error_number;
 
 	bool activated_auto_globals[8];
@@ -134,39 +135,40 @@ struct _php_core_globals {
 	bool report_zend_debug;
 
 	int last_error_type;
+	int last_error_lineno;
 	zend_string *last_error_message;
 	zend_string *last_error_file;
-	int  last_error_lineno;
 
 	char *php_sys_temp_dir;
 
 	char *disable_classes;
-	bool allow_url_include;
-#ifdef PHP_WIN32
-	bool com_initialized;
-#endif
 	zend_long max_input_nesting_level;
 	zend_long max_input_vars;
-	bool in_user_include;
 
 	char *user_ini_filename;
 	zend_long user_ini_cache_ttl;
 
 	char *request_order;
 
+	char *mail_log;
 	bool mail_x_header;
 	bool mail_mixed_lf_and_crlf;
-	char *mail_log;
 
 	bool in_error_log;
 
+	bool allow_url_include;
+#ifdef PHP_WIN32
+	bool com_initialized;
+#endif
+	bool in_user_include;
+
 #ifdef PHP_WIN32
 	bool windows_show_crt_warning;
 #endif
 
+	bool have_called_openlog;
 	zend_long syslog_facility;
 	char *syslog_ident;
-	bool have_called_openlog;
 	zend_long syslog_filter;
 	zend_long error_log_mode;
 };