0.8.12.35:

[sbcl.git] / src / code / sxhash.lisp

diff --git a/src/code/sxhash.lisp b/src/code/sxhash.lisp
index c2b7027..2afbee6 100644 (file)
--- a/src/code/sxhash.lisp
+++ b/src/code/sxhash.lisp
@@ -103,18 +103,29 @@
 (deftransform sxhash ((x) (symbol))
   (if #+sb-xc-host nil #-sb-xc-host (constant-lvar-p x)
       (sxhash (lvar-value x))
-      ;; Cache the value of the symbol's sxhash in the symbol-hash slot.
-      '(let ((result (symbol-hash x)))
-       ;; 0 marks uninitialized slot. We can't use negative values
-       ;; for the uninitialized slots since NIL might be located so
-       ;; high in memory on some platforms that its SYMBOL-HASH
-       ;; (which contains NIL itself) is a negative fixnum.
-       (if (= 0 result)
-           (let ((sxhash (%sxhash-simple-string (symbol-name x))))
-             ;; We could do a (logior sxhash #x10000000) to ensure
-             ;; that we never store a 0 in the slot. However, it's
-             ;; such an unlikely event (1/5e8?) that it makes more
-             ;; sense to optimize for the common case...
-             (%set-symbol-hash x sxhash)
-             sxhash)
-           result))))
+      (if (csubtypep (lvar-type x) (specifier-type 'null))
+         ;; FIXME: this isn't in fact as optimized as it could be;
+         ;; this does a memory load, whereas (because we know the
+         ;; layout of NIL) we could simply take the address of NIL
+         ;; (or the contents of NULL-TN) and mask off the appropriate
+         ;; bits, since SYMBOL-HASH of NIL is also NIL's CDR, which
+         ;; is NIL.  -- CSR, 2004-07-14
+         '(symbol-hash x)
+         ;; Cache the value of the symbol's sxhash in the symbol-hash
+         ;; slot.
+         '(let ((result (symbol-hash x)))
+           ;; 0 marks uninitialized slot. We can't use negative
+           ;; values for the uninitialized slots since NIL might be
+           ;; located so high in memory on some platforms that its
+           ;; SYMBOL-HASH (which contains NIL itself) is a negative
+           ;; fixnum.
+           (if (= 0 result)
+               (let ((sxhash (%sxhash-simple-string (symbol-name x))))
+                 ;; We could do a (logior sxhash #x10000000) to
+                 ;; ensure that we never store a 0 in the
+                 ;; slot. However, it's such an unlikely event
+                 ;; (1/5e8?) that it makes more sense to optimize for
+                 ;; the common case...
+                 (%set-symbol-hash x sxhash)
+                 sxhash)
+               result)))))