src/runtime/forwarding-ptr.h

   1 #ifndef _FORWARDING_PTR_H_
   2 #define _FORWARDING_PTR_H_
   3
   4 #ifndef LISP_FEATURE_GENCGC
   5 inline static boolean
   6 in_gc_p(void) {
   7     return current_dynamic_space == from_space;
   8 }
   9 #endif
  10
  11 inline static boolean
  12 forwarding_pointer_p(lispobj *pointer) {
  13     lispobj first_word=*pointer;
  14 #ifdef LISP_FEATURE_GENCGC
  15     return (first_word == 0x01);
  16 #else
  17     // FIXME: change 5c0d71f92c371769f911e6a2ac60b2dd9fbde349 added
  18     // an extra test here, which theoretically slowed things down.
  19     // This was in response to 044e22192c25578efceedba042554dc9a96124c6
  20     // which caused cheneygc to break. But now the latter revision has been
  21     // reverted due to performance degradation in gencgc.
  22     // The right fix is probably that search_spaces() should use its own
  23     // special version of gc_search_space for ldb. That is unfortunately
  24     // made difficult by the call chain:
  25     //   search_spaces() -> search_{foo}_space() -> gc_search_space().
  26     // which requires informing gc_search_space() to be more careful,
  27     // and similarly forwarding_pointer_p().
  28     return (is_lisp_pointer(first_word)
  29             && in_gc_p() /* cheneygc new_space_p() is broken when not in gc */
  30             && new_space_p(first_word));
  31 #endif
  32 }
  33
  34 static inline lispobj
  35 forwarding_pointer_value(lispobj *pointer) {
  36 #ifdef LISP_FEATURE_GENCGC
  37     return pointer[1];
  38 #else
  39     return pointer[0];
  40 #endif
  41 }
  42 static inline lispobj
  43 set_forwarding_pointer(lispobj *pointer, lispobj newspace_copy) {
  44   // The object at 'pointer' might already have been forwarded,
  45   // but that's ok. Such occurs primarily when dealing with
  46   // code components, because code can be forwarded by scavenging any
  47   // pointer to a function that resides within the code.
  48   // Testing whether the object had been forwarded would just slow
  49   // things down, so we blindly stomp on whatever was there.
  50   // Unfortunately this also implies we can't assert
  51   // that we're operating on a not-yet-forwarded object here.
  52 #ifdef LISP_FEATURE_GENCGC
  53     pointer[0]=0x01;
  54     pointer[1]=newspace_copy;
  55 #else
  56     pointer[0]=newspace_copy;
  57 #endif
  58     return newspace_copy;
  59 }
  60
  61 #endif