diff options
Diffstat (limited to 'src/lisp.h')
| -rw-r--r-- | src/lisp.h | 90 |
1 files changed, 55 insertions, 35 deletions
diff --git a/src/lisp.h b/src/lisp.h index 78c25f97dc8..7e365e8f478 100644 --- a/src/lisp.h +++ b/src/lisp.h @@ -229,7 +229,7 @@ extern bool suppress_checking EXTERNALLY_VISIBLE; USE_LSB_TAG not only requires the least 3 bits of pointers returned by malloc to be 0 but also needs to be able to impose a mult-of-8 alignment on some non-GC Lisp_Objects, all of which are aligned via - GCALIGNED_UNION at the end of a union. */ + GCALIGNED_UNION_MEMBER, GCALIGNED_STRUCT_MEMBER, and GCALIGNED_STRUCT. */ enum Lisp_Bits { @@ -282,7 +282,35 @@ error !; # define GCALIGNMENT 1 #endif -#define GCALIGNED_UNION char alignas (GCALIGNMENT) gcaligned; +/* If a struct is always allocated by the GC and is therefore always + GC-aligned, put GCALIGNED_STRUCT after its closing '}'; this can + help the compiler generate better code. + + To cause a union to have alignment of at least GCALIGNMENT, put + GCALIGNED_UNION_MEMBER in its member list. Similarly for a struct + and GCALIGNED_STRUCT_MEMBER, although this may make the struct a + bit bigger on non-GCC platforms. Any struct using + GCALIGNED_STRUCT_MEMBER should also use GCALIGNED_STRUCT. + + Although these macros are reasonably portable, they are not + guaranteed on non-GCC platforms, as C11 does not require support + for alignment to GCALIGNMENT and older compilers may ignore + alignment requests. For any type T where garbage collection + requires alignment, use verify (GCALIGNED (T)) to verify the + requirement on the current platform. Types need this check if + their objects can be allocated outside the garbage collector. For + example, struct Lisp_Symbol needs the check because of lispsym and + struct Lisp_Cons needs it because of STACK_CONS. */ + +#define GCALIGNED_UNION_MEMBER char alignas (GCALIGNMENT) gcaligned; +#if HAVE_STRUCT_ATTRIBUTE_ALIGNED +# define GCALIGNED_STRUCT_MEMBER +# define GCALIGNED_STRUCT __attribute__ ((aligned (GCALIGNMENT))) +#else +# define GCALIGNED_STRUCT_MEMBER GCALIGNED_UNION_MEMBER +# define GCALIGNED_STRUCT +#endif +#define GCALIGNED(type) (alignof (type) % GCALIGNMENT == 0) /* Lisp_Word is a scalar word suitable for holding a tagged pointer or integer. Usually it is a pointer to a deliberately-incomplete type @@ -751,10 +779,10 @@ struct Lisp_Symbol /* Next symbol in obarray bucket, if the symbol is interned. */ struct Lisp_Symbol *next; } s; - GCALIGNED_UNION + GCALIGNED_UNION_MEMBER } u; }; -verify (alignof (struct Lisp_Symbol) % GCALIGNMENT == 0); +verify (GCALIGNED (struct Lisp_Symbol)); /* Declare a Lisp-callable function. The MAXARGS parameter has the same meaning as in the DEFUN macro, and is used to construct a prototype. */ @@ -843,7 +871,9 @@ typedef EMACS_UINT Lisp_Word_tag; and PSEUDOVECTORP cast their pointers to union vectorlike_header *, because when two such pointers potentially alias, a compiler won't incorrectly reorder loads and stores to their size fields. See - Bug#8546. */ + Bug#8546. This union formerly contained more members, and there's + no compelling reason to change it to a struct merely because the + number of members has been reduced to one. */ union vectorlike_header { /* The main member contains various pieces of information: @@ -866,20 +896,7 @@ union vectorlike_header Current layout limits the pseudovectors to 63 PVEC_xxx subtypes, 4095 Lisp_Objects in GC-ed area and 4095 word-sized other slots. */ ptrdiff_t size; - /* Align the union so that there is no padding after it. - This is needed for the following reason: - If the alignment constraint of Lisp_Object is greater than the size of - vectorlike_header (e.g. with-wide-int), vectorlike objects which have - 0 Lisp_Object fields and whose 1st field has a smaller alignment - constraint than Lisp_Object may end up with their 1st field "before - pseudovector index 0", in which case PSEUDOVECSIZE will return - a "negative" number. We could fix PSEUDOVECSIZE, but it's easier to - just force rounding up the size of vectorlike_header to the alignment - of Lisp_Object. */ - Lisp_Object align; - GCALIGNED_UNION }; -verify (alignof (union vectorlike_header) % GCALIGNMENT == 0); INLINE bool (SYMBOLP) (Lisp_Object x) @@ -1251,10 +1268,10 @@ struct Lisp_Cons struct Lisp_Cons *chain; } u; } s; - GCALIGNED_UNION + GCALIGNED_UNION_MEMBER } u; }; -verify (alignof (struct Lisp_Cons) % GCALIGNMENT == 0); +verify (GCALIGNED (struct Lisp_Cons)); INLINE bool (NILP) (Lisp_Object x) @@ -1373,10 +1390,10 @@ struct Lisp_String unsigned char *data; } s; struct Lisp_String *next; - GCALIGNED_UNION + GCALIGNED_UNION_MEMBER } u; }; -verify (alignof (struct Lisp_String) % GCALIGNMENT == 0); +verify (GCALIGNED (struct Lisp_String)); INLINE bool STRINGP (Lisp_Object x) @@ -1507,7 +1524,7 @@ struct Lisp_Vector { union vectorlike_header header; Lisp_Object contents[FLEXIBLE_ARRAY_MEMBER]; - }; + } GCALIGNED_STRUCT; INLINE bool (VECTORLIKEP) (Lisp_Object x) @@ -1599,7 +1616,7 @@ struct Lisp_Bool_Vector The bits are in little-endian order in the bytes, and the bytes are in little-endian order in the words. */ bits_word data[FLEXIBLE_ARRAY_MEMBER]; - }; + } GCALIGNED_STRUCT; /* Some handy constants for calculating sizes and offsets, mostly of vectorlike objects. */ @@ -1765,7 +1782,8 @@ memclear (void *p, ptrdiff_t nbytes) ones that the GC needs to trace). */ #define PSEUDOVECSIZE(type, nonlispfield) \ - ((offsetof (type, nonlispfield) - header_size) / word_size) + (offsetof (type, nonlispfield) < header_size \ + ? 0 : (offsetof (type, nonlispfield) - header_size) / word_size) /* Compute A OP B, using the unsigned comparison operator OP. A and B should be integer expressions. This is not the same as @@ -1830,7 +1848,7 @@ struct Lisp_Char_Table /* These hold additional data. It is a vector. */ Lisp_Object extras[FLEXIBLE_ARRAY_MEMBER]; - }; + } GCALIGNED_STRUCT; INLINE bool CHAR_TABLE_P (Lisp_Object a) @@ -1942,7 +1960,9 @@ struct Lisp_Subr const char *symbol_name; const char *intspec; EMACS_INT doc; - }; + GCALIGNED_STRUCT_MEMBER + } GCALIGNED_STRUCT; +verify (GCALIGNED (struct Lisp_Subr)); INLINE bool SUBRP (Lisp_Object a) @@ -2194,7 +2214,7 @@ struct Lisp_Hash_Table /* Next weak hash table if this is a weak hash table. The head of the list is in weak_hash_tables. */ struct Lisp_Hash_Table *next_weak; -}; +} GCALIGNED_STRUCT; INLINE bool @@ -2313,7 +2333,7 @@ struct Lisp_Marker used to implement the functionality of markers, but rather to (ab)use markers as a cache for char<->byte mappings). */ ptrdiff_t bytepos; -}; +} GCALIGNED_STRUCT; /* START and END are markers in the overlay's buffer, and PLIST is the overlay's property list. */ @@ -2335,13 +2355,13 @@ struct Lisp_Overlay Lisp_Object end; Lisp_Object plist; struct Lisp_Overlay *next; - }; + } GCALIGNED_STRUCT; struct Lisp_Misc_Ptr { union vectorlike_header header; void *pointer; - }; + } GCALIGNED_STRUCT; extern Lisp_Object make_misc_ptr (void *); @@ -2388,7 +2408,7 @@ struct Lisp_User_Ptr union vectorlike_header header; void (*finalizer) (void *); void *p; -}; +} GCALIGNED_STRUCT; #endif /* A finalizer sentinel. */ @@ -2404,7 +2424,7 @@ struct Lisp_Finalizer /* Circular list of all active weak references. */ struct Lisp_Finalizer *prev; struct Lisp_Finalizer *next; - }; + } GCALIGNED_STRUCT; INLINE bool FINALIZERP (Lisp_Object x) @@ -2616,7 +2636,7 @@ struct Lisp_Float double data; struct Lisp_Float *chain; } u; - }; + } GCALIGNED_STRUCT; INLINE bool (FLOATP) (Lisp_Object x) @@ -3946,7 +3966,7 @@ struct Lisp_Module_Function ptrdiff_t min_arity, max_arity; emacs_subr subr; void *data; -}; +} GCALIGNED_STRUCT; INLINE bool MODULE_FUNCTIONP (Lisp_Object o) |