Micro-optimize type tests using widetag on x86-64.

Change %TEST-HEADERS not to load the widetag of the value to be tested
into AL if only a single comparison is needed on it, instead do the
comparison directly with the memory operand. This is smaller and needs
fewer execution ressources.

This is a port of what is done on x86 already, with two modifications:

 * Widetag ranges starting with the smallest widetag or ending with the
   largest widetag use the memory operand here but go through AL on x86.

 * x86 exploits the specially choosen widetag values of components of
   compound types (like BASE-STRING) to test for these types with only
   an additional "and" operation but still only a single comparison.
   This can't be done on x86-64 currently as under 64-bit wordsize the
   widetag values are different and don't have the necessary property
   (namely to differ in only a single bit).

Additionally, when AL needs to be loaded, use EAX instead so as not to
write a partial register (as recommended by the processors' optimization
guides). Same code size, potentially faster.

Silence a "deleting unreachable code" warning during build by removing
an IF and the corresponding unreachable expression.

diff --git a/src/compiler/x86-64/type-vops.lisp b/src/compiler/x86-64/type-vops.lisp
index 0e8c9c4..47b18d3 100644 (file)
--- a/src/compiler/x86-64/type-vops.lisp
+++ b/src/compiler/x86-64/type-vops.lisp
@@ -83,7 +83,8 @@
 (defun %test-headers (value target not-p function-p headers
                             &optional (drop-through (gen-label)))
   (let ((lowtag (if function-p fun-pointer-lowtag other-pointer-lowtag)))
-    (multiple-value-bind (equal less-or-equal greater-or-equal when-true when-false)
+    (multiple-value-bind (equal less-or-equal greater-or-equal when-true
+                                when-false)
         ;; EQUAL, LESS-OR-EQUAL, and GREATER-OR-EQUAL are the conditions
         ;; for branching to TARGET.  WHEN-TRUE and WHEN-FALSE are the
         ;; labels to branch to when we know it's true and when we know
@@ -92,14 +93,30 @@
             (values :ne :a :b drop-through target)
             (values :e :na :nb target drop-through))
       (%test-lowtag value when-false t lowtag)
-      (inst mov al-tn (make-ea :byte :base value :disp (- lowtag)))
-      (do ((remaining headers (cdr remaining)))
+      (do ((remaining headers (cdr remaining))
+           ;; It is preferable (smaller and faster code) to directly
+           ;; compare the value in memory instead of loading it into
+           ;; a register first. Find out if this is possible and set
+           ;; WIDETAG-TN accordingly. If impossible, generate the
+           ;; register load.
+           ;; Compared to x86 we additionally optimize the cases of a
+           ;; range starting with BIGNUM-WIDETAG or ending with
+           ;; COMPLEX-ARRAY-WIDETAG.
+           (widetag-tn (if (and (null (cdr headers))
+                                (or (atom (car headers))
+                                    (= (caar headers) bignum-widetag)
+                                    (= (cdar headers) complex-array-widetag)))
+                           (make-ea :byte :base value :disp (- lowtag))
+                           (progn
+                             (inst mov eax-tn (make-ea :dword :base value
+                                                       :disp (- lowtag)))
+                             al-tn))))
           ((null remaining))
         (let ((header (car remaining))
               (last (null (cdr remaining))))
           (cond
            ((atom header)
-            (inst cmp al-tn header)
+            (inst cmp widetag-tn header)
             (if last
                 (inst jmp equal target)
                 (inst jmp :e when-true)))
@@ -108,12 +125,12 @@
                    (end (cdr header)))
                (cond
                  ((= start bignum-widetag)
-                  (inst cmp al-tn end)
+                  (inst cmp widetag-tn end)
                   (if last
                       (inst jmp less-or-equal target)
                       (inst jmp :be when-true)))
                  ((= end complex-array-widetag)
-                  (inst cmp al-tn start)
+                  (inst cmp widetag-tn start)
                   (if last
                       (inst jmp greater-or-equal target)
                       (inst jmp :b when-false)))
@@ -121,9 +138,7 @@
                   (inst cmp al-tn start)
                   (inst jmp :b when-false)
                   (inst cmp al-tn end)
-                  (if last
-                      (inst jmp less-or-equal target)
-                      (inst jmp :be when-true)))
+                  (inst jmp :be when-true))
                  (t
                   (inst sub al-tn start)
                   (inst cmp al-tn (- end start))