pike.git/ src/ svalue.h

2014-06-19

2014-06-19 15:55:43 by Per Hedbor <ph@opera.com>

• 7666f80613fd36cd685dcdfca2dc2ce6f6d73b50 (28 lines) (+22/-6) ^{[ Show | Annotate ]}
  Branch: 8.0

Faster svalue type/subtype setting

The code generated for setting two shorts (on x86/x86_64 and arm at least) is
very sub-optimal, especially with gcc, for some reason:

Old push_int(0):
movq Pike_interpreter_pointer(%rip), %rdx
movq (%rdx), %rax
leaq 16(%rax), %rcx
movq %rcx, (%rdx)
xorl %edx, %edx
xorl %ecx, %ecx
movw %dx, (%rax)
movw %cx, 2(%rax)
movq $0, 8(%rax)

New push_int(0):
movq Pike_interpreter_pointer(%rip), %rdx
movq (%rdx), %rax
leaq 16(%rax), %rcx
movq %rcx, (%rdx)
movq $0, (%rax)
movq $0, 8(%rax)

Except for the lower number of instructions there is an additional
benefit: The old code triggered a read-modify-write operation on most
modern x86 CPU:s, all to preserve the undefined data between subtype
and the value of the svalue. This could be fixed by changing the type
and subtype to be 32-bit instead of 16-bit, but that is a bigger
change.

94:    */   struct svalue   { -  unsigned INT16 type; /**< the data type, see PIKE_T_... */ -  unsigned INT16 subtype; /**< used to store the zero type, among others */ +  unsigned short type; /**< the data type, see PIKE_T_... */ +  unsigned short subtype; /**< used to store the zero type, among others */    union anything u; /**< contains the value */   };    -  + struct fast_svalue + { +  ptrdiff_t type_subtype; +  union anything u; + }; +  + #if PIKE_BYTEORDER == 1234 + #define TYPE_SUBTYPE(X,Y) ((X)|((Y)<<16)) + #else + #define TYPE_SUBTYPE(X,Y) ((Y)|((X)<<16)) + #endif +    #define TYPEOF(SVAL) ((SVAL).type)   #define SUBTYPEOF(SVAL) ((SVAL).subtype) -  + #define SET_SVAL_TYPE_SUBTYPE(SVAL, TYPE, SUBTYPE) \ +  (((struct fast_svalue*)&(SVAL))->type_subtype=TYPE_SUBTYPE(TYPE,SUBTYPE)) +    #define SET_SVAL_TYPE(SVAL, TYPE) (TYPEOF(SVAL) = (TYPE))   #define SET_SVAL_SUBTYPE(SVAL, TYPE) (SUBTYPEOF(SVAL) = (TYPE)) -  +    #define SET_SVAL(SVAL, TYPE, SUBTYPE, FIELD, EXPR) do { \    /* Set the type afterwards to avoid a clobbered \    * svalue in case EXPR throws. */ \ -  struct svalue * __sv_ptr = &( SVAL ); \ +  struct fast_svalue * __sv_ptr = (struct fast_svalue *)&( SVAL ); \    __sv_ptr->u.FIELD = (EXPR); \ -  SET_SVAL_TYPE(*__sv_ptr, (TYPE)); \ -  SET_SVAL_SUBTYPE(*__sv_ptr, (SUBTYPE)); \ +  __sv_ptr->type_subtype = TYPE_SUBTYPE(TYPE,SUBTYPE);\    } while(0)      /*   */ - #define INVALIDATE_SVAL(SVAL) SET_SVAL_TYPE(SVAL, 99) /* an invalid type */ + #define INVALIDATE_SVAL(SVAL) SET_SVAL_TYPE_SUBTYPE(SVAL, 99,0) /* an invalid type */      /* The native types.    *