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| author | Paul Eggert <eggert@cs.ucla.edu> | 2011-04-25 00:14:46 -0700 |
|---|---|---|
| committer | Paul Eggert <eggert@cs.ucla.edu> | 2011-04-25 00:14:46 -0700 |
| commit | eab3844f965646b62e242aa622754b86d1fd3444 (patch) | |
| tree | 10246105e5facc5d61ccf797dfa05debdb1877c1 /src/bytecode.c | |
| parent | 0df1eac54fdf82a80a7611fe421d94a23ebd4a0a (diff) | |
| download | emacs-eab3844f965646b62e242aa622754b86d1fd3444.tar.gz | |
lisp.h: Fix a problem with aliasing and vector headers.
GCC 4.6.0 optimizes based on type-based alias analysis. For
example, if b is of type struct buffer * and v of type struct
Lisp_Vector *, then gcc -O2 was incorrectly assuming that &b->size
!= &v->size, and therefore "v->size = 1; b->size = 2; return
v->size;" must therefore return 1. This assumption is incorrect
for Emacs, since it type-puns struct Lisp_Vector * with many other
types. To fix this problem, this patch adds a new type struct
vector_header that documents the constraints on layout of vectors
and pseudovectors, and helps optimizing compilers not get fooled
by Emacs's type punning. It also adds the macros XSETTYPED_PVECTYPE
XSETTYPED_PSEUDOVECTOR, TYPED_PSEUDOVECTORP, for similar reasons.
* lisp.h (XVECTOR_SIZE): New convenience macro. All previous uses of
XVECTOR (foo)->size replaced to use this macro, to avoid the hassle
of writing XVECTOR (foo)->header.size.
(XVECTOR_HEADER_SIZE): New macro, for use in XSETPSEUDOVECTOR.
(XSETTYPED_PVECTYPE): New macro, specifying the name of the size
member.
(XSETPVECTYPE): Rewrite in terms of new macro.
(XSETPVECTYPESIZE): New macro, specifying both type and size.
This is a bit clearer, and further avoids the possibility of
undesirable aliasing.
(XSETTYPED_PSEUDOVECTOR): New macro, specifying the size.
(XSETPSEUDOVECTOR): Rewrite in terms of XSETTYPED_PSEUDOVECTOR
and XVECTOR_HEADER_SIZE.
(XSETSUBR): Rewrite in terms of XSETTYPED_PSEUDOVECTOR and XSIZE,
since Lisp_Subr is a special case (no "next" field).
(ASIZE): Rewrite in terms of XVECTOR_SIZE.
(struct vector_header): New type.
(TYPED_PSEUDOVECTORP): New macro, also specifying the C type of the
object, to help avoid aliasing.
(PSEUDOVECTORP): Rewrite in terms of TYPED_PSEUDOVECTORP.
(SUBRP): Likewise, since Lisp_Subr is a special case.
* lisp.h (struct Lisp_Vector, struct Lisp_Char_Table):
(struct Lisp_Sub_Char_Table, struct Lisp_Bool_Vector):
(struct Lisp_Hash_Table): Combine first two members into a single
struct vector_header member. All uses of "size" and "next" members
changed to be "header.size" and "header.next".
* buffer.h (struct buffer): Likewise.
* font.h (struct font_spec, struct font_entity, struct font): Likewise.
* frame.h (struct frame): Likewise.
* process.h (struct Lisp_Process): Likewise.
* termhooks.h (struct terminal): Likewise.
* window.c (struct save_window_data, struct saved_window): Likewise.
* window.h (struct window): Likewise.
* alloc.c (allocate_buffer, Fmake_bool_vector, allocate_pseudovector):
Use XSETPVECTYPESIZE, not XSETPVECTYPE, to avoid aliasing problems.
* buffer.c (init_buffer_once): Likewise.
* lread.c (defsubr): Use XSETTYPED_PVECTYPE, since Lisp_Subr is a
special case.
* process.c (Fformat_network_address): Use local var for size,
for brevity.
Diffstat (limited to 'src/bytecode.c')
| -rw-r--r-- | src/bytecode.c | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/src/bytecode.c b/src/bytecode.c index 3bbd8831633..839e0f7d54e 100644 --- a/src/bytecode.c +++ b/src/bytecode.c @@ -467,7 +467,7 @@ exec_byte_code (Lisp_Object bytestr, Lisp_Object vector, Lisp_Object maxdepth, CHECK_NUMBER (maxdepth); #ifdef BYTE_CODE_SAFE - const_length = XVECTOR (vector)->size; + const_length = XVECTOR_SIZE (vector); #endif if (STRING_MULTIBYTE (bytestr)) |