;;; 'def.*even-fixnum-lowtag' can find them.
;;; Tags for the main low-level types are stored in the low n (usually three)
-;;; bits to identify the type of a machine word. Certain constraints
+;;; bits to identify the type of a machine word. Certain constraints
;;; apply:
;;; * EVEN-FIXNUM-LOWTAG and ODD-FIXNUM-LOWTAG must be 0 and 4: code
;;; which shifts left two places to convert raw integers to tagged
;;; fixnums is ubiquitous.
-;;; * LIST-POINTER-LOWTAG + N-WORD-BYTES = OTHER-POINTER-LOWTAG: NIL
+;;; * LIST-POINTER-LOWTAG + N-WORD-BYTES = OTHER-POINTER-LOWTAG: NIL
;;; is both a cons and a symbol (at the same address) and depends on this.
;;; See the definition of SYMBOL in objdef.lisp
;;; * OTHER-POINTER-LOWTAG > 4: Some code in the SPARC backend,
;;; PSEUDO-ATOMIC is on, doesn't strip the low bits of reg_ALLOC
;;; before ORing in OTHER-POINTER-LOWTAG within a PSEUDO-ATOMIC
;;; section.
-;;; * OTHER-IMMEDIATE-0-LOWTAG are spaced 4 apart: various code wants to
+;;; * OTHER-IMMEDIATE-0-LOWTAG are spaced 4 apart: various code wants to
;;; iterate through these
+;;; * Allocation code on Alpha wants lowtags for heap-allocated
+;;; objects to be odd.
;;; (These are just the ones we know about as of sbcl-0.7.1.22. There
;;; might easily be more, since these values have stayed highly
;;; constrained for more than a decade, an inviting target for
;;; ANDcc tag, 0xA6, tag
;;; JNE tag, label
;;;
-;;; rather than two separate tests and jumps
+;;; rather than two separate tests and jumps
(defenum (:suffix -widetag
;; The first widetag must be greater than SB!VM:LOWTAG-LIMIT
;; otherwise code in generic/early-type-vops will suffer
;; a long, horrible death. --njf, 2004-08-09
- :start (+ (ash 1 n-lowtag-bits) other-immediate-0-lowtag)
- :step 4)
+ :start (+ (ash 1 n-lowtag-bits) other-immediate-0-lowtag)
+ :step 4)
;; NOTE: the binary numbers off to the side are only valid for 32-bit
;; ports; add #b1000 if you want to know the values for 64-bit ports.
;; And note that the numbers get a little scrambled further down.
instance-header ; 01010010
fdefn ; 01010110
- unused00 ; 01011010
+ no-tls-value-marker ; 01011010
unused01 ; 01011110
unused02 ; 01100010
unused03 ; 01100110