X-Git-Url: http://repo.macrolet.net/gitweb/?a=blobdiff_plain;f=src%2Fcompiler%2Fx86-64%2Fmove.lisp;h=a5de78c2b817caab9a203673b904161ca99378c7;hb=085501b44cc1cbdd9e260139d30b383372ddd1b8;hp=a9a7ec5023dd24b6c126258233ebe5ead0d27207;hpb=0d871fd7a98fc4af92a8b942a1154761466ad8c9;p=sbcl.git

diff --git a/src/compiler/x86-64/move.lisp b/src/compiler/x86-64/move.lisp
index a9a7ec5..a5de78c 100644
--- a/src/compiler/x86-64/move.lisp
+++ b/src/compiler/x86-64/move.lisp
@@ -1,4 +1,4 @@
-;;;; the x86 VM definition of operand loading/saving and the MOVE vop
+;;;; the x86-64 VM definition of operand loading/saving and the MOVE vop
 
 ;;;; This software is part of the SBCL system. See the README file for
 ;;;; more information.
@@ -11,6 +11,17 @@
 
 (in-package "SB!VM")
 
+(defun zeroize (tn)
+  (let ((offset (tn-offset tn)))
+    ;; Using the 32-bit instruction accomplishes the same thing and is
+    ;; one byte shorter.
+    (if (<= offset edi-offset)
+        (let ((tn (make-random-tn :kind :normal
+                                  :sc (sc-or-lose 'dword-reg)
+                                  :offset offset)))
+          (inst xor tn tn))
+        (inst xor tn tn))))
+
 (define-move-fun (load-immediate 1) (vop x y)
   ((immediate)
    (any-reg descriptor-reg))
@@ -18,7 +29,7 @@
     (etypecase val
       (integer
        (if (zerop val)
-           (inst xor y y)
+           (zeroize y)
          (inst mov y (fixnumize val))))
       (symbol
        (load-symbol y val))
@@ -28,7 +39,10 @@
 
 (define-move-fun (load-number 1) (vop x y)
   ((immediate) (signed-reg unsigned-reg))
-  (inst mov y (tn-value x)))
+  (let ((val (tn-value x)))
+    (if (zerop val)
+        (zeroize y)
+        (inst mov y val))))
 
 (define-move-fun (load-character 1) (vop x y)
   ((immediate) (character-reg))
@@ -77,7 +91,7 @@
           (etypecase val
             (integer
              (if (and (zerop val) (sc-is y any-reg descriptor-reg))
-                 (inst xor y y)
+                 (zeroize y)
                  (move-immediate y (fixnumize val) temp)))
             (symbol
              (inst mov y (+ nil-value (static-symbol-offset val))))
@@ -131,7 +145,7 @@
            (let ((val (tn-value x)))
              (etypecase val
                ((integer 0 0)
-                (inst xor y y))
+                (zeroize y))
                ((or (signed-byte 29) (unsigned-byte 29))
                 (inst mov y (fixnumize val)))
                (integer
@@ -279,12 +293,15 @@
      (aver (not (location= x y)))
      (let ((bignum (gen-label))
            (done (gen-label)))
-       (inst mov y x)
-       (inst shl y 1)
-       (inst jmp :o bignum)
-       (inst shl y 1)
-       (inst jmp :o bignum)
-       (inst shl y 1)
+       ;; We can't do the overflow check with SHL Y, 3, since the
+       ;; state of the overflow flag is only reliably set when
+       ;; shifting by 1. There used to be code here for doing "shift
+       ;; by one, check whether it overflowed" three times. But on all
+       ;; x86-64 processors IMUL is a reasonably fast instruction, so
+       ;; we can just do a straight multiply instead of trying to
+       ;; optimize it to a shift. This is both faster and smaller.
+       ;; -- JES, 2006-07-08
+       (inst imul y x (ash 1 n-fixnum-tag-bits))
        (inst jmp :o bignum)
        (emit-label done)