diff --git a/src/compiler/x86-64/alloc.lisp b/src/compiler/x86-64/alloc.lisp
index c6218c8..7b436a0 100644
--- a/src/compiler/x86-64/alloc.lisp
+++ b/src/compiler/x86-64/alloc.lisp
@@ -81,7 +81,7 @@
   (:generator 100
     (inst lea result (make-ea :byte :index words
                               :scale (ash 1 (- word-shift n-fixnum-tag-bits))
-                              :disp (+ (1- (ash 1 n-lowtag-bits))
+                              :disp (+ lowtag-mask
                                        (* vector-data-offset n-word-bytes))))
     (inst and result (lognot lowtag-mask))
     (pseudo-atomic
@@ -107,7 +107,7 @@
   (:generator 100
     (inst lea result (make-ea :byte :index words
                               :scale (ash 1 (- word-shift n-fixnum-tag-bits))
-                              :disp (+ (1- (ash 1 n-lowtag-bits))
+                              :disp (+ lowtag-mask
                                        (* vector-data-offset n-word-bytes))))
     (inst and result (lognot lowtag-mask))
     ;; FIXME: It would be good to check for stack overflow here.
@@ -208,7 +208,7 @@
           (make-ea :qword :disp (* (1+ words) n-word-bytes) :index extra
                    :scale (ash 1 (- word-shift n-fixnum-tag-bits))))
     (inst mov header bytes)
-    (inst shl header (- n-widetag-bits 3)) ; w+1 to length field
+    (inst shl header (- n-widetag-bits word-shift)) ; w+1 to length field
     (inst lea header                    ; (w-1 << 8) | type
           (make-ea :qword :base header :disp (+ (ash -2 n-widetag-bits) type)))
     (inst and bytes (lognot lowtag-mask))
diff --git a/src/compiler/x86-64/arith.lisp b/src/compiler/x86-64/arith.lisp
index 542ee54..cd626ce 100644
--- a/src/compiler/x86-64/arith.lisp
+++ b/src/compiler/x86-64/arith.lisp
@@ -220,7 +220,7 @@
   (:generator 2
     (cond ((and (sc-is x any-reg) (sc-is y any-reg) (sc-is r any-reg)
                 (not (location= x r)))
-           (inst lea r (make-ea :qword :base x :index y :scale 1)))
+           (inst lea r (make-ea :qword :base x :index y)))
           (t
            (move r x)
            (inst add r y)))))
@@ -266,7 +266,7 @@
   (:generator 5
     (cond ((and (sc-is x signed-reg) (sc-is y signed-reg) (sc-is r signed-reg)
                 (not (location= x r)))
-           (inst lea r (make-ea :qword :base x :index y :scale 1)))
+           (inst lea r (make-ea :qword :base x :index y)))
           (t
            (move r x)
            (inst add r y)))))
diff --git a/src/compiler/x86-64/array.lisp b/src/compiler/x86-64/array.lisp
index 0b24555..eefd30b 100644
--- a/src/compiler/x86-64/array.lisp
+++ b/src/compiler/x86-64/array.lisp
@@ -30,7 +30,8 @@
   (:node-var node)
   (:generator 13
     (inst lea bytes
-          (make-ea :qword :base rank
+          (make-ea :qword
+                   :index rank :scale (ash 1 (- n-word-bytes n-fixnum-tag-bits))
                    :disp (+ (* (1+ array-dimensions-offset) n-word-bytes)
                             lowtag-mask)))
     (inst and bytes (lognot lowtag-mask))
@@ -38,7 +39,7 @@
                               :disp (fixnumize (1- array-dimensions-offset))))
     (inst shl header n-widetag-bits)
     (inst or  header type)
-    (inst shr header (1- n-lowtag-bits))
+    (inst shr header n-fixnum-tag-bits)
     (pseudo-atomic
      (allocation result bytes node)
      (inst lea result (make-ea :qword :base result :disp other-pointer-lowtag))
@@ -120,7 +121,7 @@
     (let ((error (generate-error-code vop 'invalid-array-index-error
                                       array bound index))
           (index (if (sc-is index immediate)
-                   (fixnumize (tn-value index))
+                   (fixnumize (tn-value index)) ;; FIXME: might not be a 32 bit immediate
                    index)))
       (inst cmp bound index)
       ;; We use below-or-equal even though it's an unsigned test,
@@ -353,14 +354,11 @@
   (:arg-types simple-array-single-float positive-fixnum
               (:constant (constant-displacement other-pointer-lowtag
                                                 4 vector-data-offset)))
-  (:temporary (:sc unsigned-reg) dword-index)
   (:results (value :scs (single-reg)))
   (:result-types single-float)
   (:generator 5
-   (move dword-index index)
-   #!+#.(cl:if (cl:<= sb!vm:word-shift sb!vm:n-fixnum-tag-bits) '(and) '(or))
-   (inst shr dword-index (1+ (- sb!vm:n-fixnum-tag-bits sb!vm:word-shift)))
-   (inst movss value (make-ea-for-float-ref object dword-index offset 4))))
+    (inst movss value (make-ea-for-float-ref object index offset 4
+                                             :scale (ash 1 (- 2 n-fixnum-tag-bits))))))
 
 (define-vop (data-vector-ref-c-with-offset/simple-array-single-float)
   (:note "inline array access")
@@ -388,14 +386,12 @@
               (:constant (constant-displacement other-pointer-lowtag
                                                 4 vector-data-offset))
                single-float)
-  (:temporary (:sc unsigned-reg) dword-index)
   (:results (result :scs (single-reg)))
   (:result-types single-float)
   (:generator 5
-   (move dword-index index)
-   #!+#.(cl:if (cl:<= sb!vm:word-shift sb!vm:n-fixnum-tag-bits) '(and) '(or))
-   (inst shr dword-index (1+ (- sb!vm:n-fixnum-tag-bits sb!vm:word-shift)))
-   (inst movss (make-ea-for-float-ref object dword-index offset 4) value)
+   (inst movss (make-ea-for-float-ref object index offset 4
+                                      :scale (ash 1 (- 2 n-fixnum-tag-bits)))
+         value)
    (move result value)))
 
 (define-vop (data-vector-set-c-with-offset/simple-array-single-float)
diff --git a/src/compiler/x86-64/c-call.lisp b/src/compiler/x86-64/c-call.lisp
index d90427f..62427b9 100644
--- a/src/compiler/x86-64/c-call.lisp
+++ b/src/compiler/x86-64/c-call.lisp
@@ -482,7 +482,7 @@
                (alien-type-= #.(parse-alien-type 'system-area-pointer nil)
                              result-type))
            (inst mov rax [rsp]))
-          ((or (alien-single-float-type-p result-type)
+          ((or (alien-single-float-type-p result-type)  ;; This is probably wrong.
                (alien-double-float-type-p result-type))
            (inst movq xmm0 [rsp]))
           ((alien-void-type-p result-type))
diff --git a/src/compiler/x86-64/call.lisp b/src/compiler/x86-64/call.lisp
index a5a600a..78db699 100644
--- a/src/compiler/x86-64/call.lisp
+++ b/src/compiler/x86-64/call.lisp
@@ -735,7 +735,7 @@
                               (noise))
                    '((if (zerop nargs)
                          (zeroize rcx)
-                       (inst mov rcx (fixnumize nargs)))))
+                         (inst mov rcx (fixnumize nargs)))))
                ,@(cond ((eq return :tail)
                         '(;; Python has figured out what frame we should
                           ;; return to so might as well use that clue.
@@ -1163,7 +1163,7 @@
                                 :disp n-word-bytes))))
 
 (define-vop (more-arg)
-    (:translate sb!c::%more-arg)
+  (:translate sb!c::%more-arg)
   (:policy :fast-safe)
   (:args (object :scs (descriptor-reg) :to (:result 1))
          (index :scs (any-reg) :to (:result 1) :target value))
@@ -1247,7 +1247,7 @@
   (:result-types t tagged-num)
   (:note "more-arg-context")
   (:generator 5
-    (move count supplied)
+    (move count supplied) ;; FIXME: suboptimal
     ;; SP at this point points at the last arg pushed.
     ;; Point to the first more-arg, not above it.
     (inst lea context (make-ea :qword :base rsp-tn
diff --git a/src/compiler/x86-64/cell.lisp b/src/compiler/x86-64/cell.lisp
index caf86d7..b61c422 100644
--- a/src/compiler/x86-64/cell.lisp
+++ b/src/compiler/x86-64/cell.lisp
@@ -529,7 +529,7 @@
   (:result-types unsigned-num)
   (:generator 5
     (loadw tmp object 0 instance-pointer-lowtag)
-    (inst shr tmp n-widetag-bits)
+    (inst shr tmp n-widetag-bits)    ;; FIXME: suboptimal
     (inst shl tmp n-fixnum-tag-bits)
     (inst sub tmp index)
     (inst mov value (make-ea-for-raw-slot object tmp :scale (ash 1 (- word-shift n-fixnum-tag-bits))))))
diff --git a/src/compiler/x86-64/debug.lisp b/src/compiler/x86-64/debug.lisp
index 5f720fe..9446737 100644
--- a/src/compiler/x86-64/debug.lisp
+++ b/src/compiler/x86-64/debug.lisp
@@ -43,7 +43,9 @@
     (move temp offset)
     (inst neg temp)
     (inst mov result
-          (make-ea :qword :base sap :disp (frame-byte-offset 0) :index temp))))
+          (make-ea :qword :base sap :disp (frame-byte-offset 0)
+                   :index temp
+                   :scale (ash 1 (- word-shift n-fixnum-tag-bits))))))
 
 (define-vop (read-control-stack-c)
   (:translate stack-ref)
@@ -71,7 +73,9 @@
     (move temp offset)
     (inst neg temp)
     (inst mov
-          (make-ea :qword :base sap :disp (frame-byte-offset 0) :index temp)
+          (make-ea :qword :base sap :disp (frame-byte-offset 0)
+                   :index temp
+                   :scale (ash 1 (- word-shift n-fixnum-tag-bits)))
           value)
     (move result value)))
 
@@ -101,7 +105,7 @@
       (loadw temp thing 0 lowtag)
       (inst shr temp n-widetag-bits)
       (inst jmp :z bogus)
-      (inst shl temp (1- (integer-length n-word-bytes)))
+      (inst shl temp (1- word-shift))
       (unless (= lowtag other-pointer-lowtag)
         (inst add temp (- lowtag other-pointer-lowtag)))
       (move code thing)
diff --git a/src/compiler/x86-64/move.lisp b/src/compiler/x86-64/move.lisp
index c2c76b5..c81e87b 100644
--- a/src/compiler/x86-64/move.lisp
+++ b/src/compiler/x86-64/move.lisp
@@ -266,7 +266,7 @@
                    :from (:argument 0) :to (:result 0) :target y) eax)
   (:generator 4
     (move eax x)
-    (inst test al-tn 7)                 ; a symbolic constant for this
+    (inst test al-tn fixnum-tag-mask)   ; a symbolic constant for this
     (inst jmp :z FIXNUM)                ; would be nice
     (loadw y eax bignum-digits-offset other-pointer-lowtag)
     (inst jmp DONE)
@@ -346,7 +346,7 @@
   (:generator 20
     (aver (not (location= x y)))
     (let ((done (gen-label)))
-      (inst mov y #.(ash (1- (ash 1 (1+ n-fixnum-tag-bits)))
+      (inst mov y #.(ash (1- (ash 1 (1+ n-fixnum-tag-bits))) ;; FIXME: can just test MSB
                          (- n-word-bits n-fixnum-tag-bits 1)))
       ;; The assembly routines test the sign flag from this one, so if
       ;; you change stuff here, make sure the sign flag doesn't get
diff --git a/src/compiler/x86-64/nlx.lisp b/src/compiler/x86-64/nlx.lisp
index 4cc02fd..70bb788 100644
--- a/src/compiler/x86-64/nlx.lisp
+++ b/src/compiler/x86-64/nlx.lisp
@@ -187,7 +187,7 @@
 (define-vop (nlx-entry-multiple)
   (:args (top)
          (source)
-         (count :target rcx))
+         (count :target rcx))   ; tagged fixnum
   ;; Again, no SC restrictions for the args, 'cause the loading would
   ;; happen before the entry label.
   (:info label)
@@ -212,7 +212,7 @@
     (inst sub rdi n-word-bytes)
     (move rcx count)                    ; fixnum words == bytes
     (move num rcx)
-    (inst shr rcx word-shift)           ; word count for <rep movs>
+    (inst shr rcx n-fixnum-tag-bits)           ; word count for <rep movs>
     ;; If we got zero, we be done.
     (inst jrcxz DONE)
     ;; Copy them down.
diff --git a/src/compiler/x86-64/system.lisp b/src/compiler/x86-64/system.lisp
index ce91fb4..a1d7e80 100644
--- a/src/compiler/x86-64/system.lisp
+++ b/src/compiler/x86-64/system.lisp
@@ -40,11 +40,11 @@
     (inst jmp :e FUNCTION-PTR)
 
     ;; Pick off structures and list pointers.
-    (inst test al-tn 1)
+    (inst test al-tn 1) ;; FIXME: is that right?
     (inst jmp :ne DONE)
 
     ;; Pick off fixnums.
-    (inst and al-tn 7)
+    (inst and al-tn fixnum-tag-mask)
     (inst jmp :e DONE)
 
     ;; must be an other immediate
@@ -122,7 +122,7 @@
   (:generator 6
     (move eax data)
     (inst shl eax (- n-widetag-bits n-fixnum-tag-bits))
-    (inst mov al-tn (make-ea :byte :base x :disp (- other-pointer-lowtag)))
+    (inst mov al-tn (make-ea :byte :base x :disp (- other-pointer-lowtag))) ; FIXME: suboptimal...
     (storew eax x 0 other-pointer-lowtag)
     (move res x)))
 
@@ -135,8 +135,8 @@
     (move res ptr)
     ;; Mask the lowtag, and shift the whole address into a positive
     ;; fixnum.
-    (inst and res (lognot lowtag-mask))
-    (inst shr res 1)))
+    (inst shr res 1)
+    (inst and res (lognot fixnum-tag-mask))))
 
 (define-vop (make-other-immediate-type)
   (:args (val :scs (any-reg descriptor-reg) :target res)
diff --git a/src/compiler/x86-64/type-vops.lisp b/src/compiler/x86-64/type-vops.lisp
index d8e49e0..10d47d3 100644
--- a/src/compiler/x86-64/type-vops.lisp
+++ b/src/compiler/x86-64/type-vops.lisp
@@ -23,7 +23,7 @@
                         :disp (frame-byte-offset (tn-offset value))))
               (t
                value))
-        sb!vm::fixnum-tag-mask))
+        fixnum-tag-mask))
 
 (defun %test-fixnum (value target not-p)
   (generate-fixnum-test value)