diff options
Diffstat (limited to 'src/lisp.h')
| -rw-r--r-- | src/lisp.h | 18 |
1 files changed, 2 insertions, 16 deletions
diff --git a/src/lisp.h b/src/lisp.h index 8c274cddb56..47570ebee74 100644 --- a/src/lisp.h +++ b/src/lisp.h @@ -197,22 +197,8 @@ extern int suppress_checking EXTERNALLY_VISIBLE; # if defined DECL_ALIGN /* On hosts where VALBITS is greater than the pointer width in bits, USE_LSB_TAG is: - - a. unnecessary, because the top bits of an EMACS_INT are unused, - - b. slower, because it typically requires extra masking, and - - c. harmful, because it can create Lisp_Object values that are so scrambled - that mark_maybe_object cannot decipher them. mark_maybe_object assumes - that EMACS_INT values are contiguous, but a host where EMACS_INT is - wider than a pointer might allocate the top half of an EMACS_INT in - (say) a 32-bit word on the stack, putting the bottom half in a 32-bit - register that is saved elsewhere in a jmp_buf. When this happens, - since USE_LSB_TAG is not defined the bottom half alone is a valid - pointer that mark_maybe_pointer can follow; but if USE_LSB_TAG were - defined, the bottom half would not be a valid pointer and neither - mark_maybe_object nor mark_maybe_pointer would follow it. - + a. unnecessary, because the top bits of an EMACS_INT are unused, and + b. slower, because it typically requires extra masking. So, define USE_LSB_TAG only on hosts where it might be useful. */ # if UINTPTR_MAX >> VALBITS != 0 # define USE_LSB_TAG |