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List:       sbcl-commits
Subject:    [Sbcl-commits] master: Micro-optimize some type tests on x86-64 for code size.
From:       "Lutz Euler" <leuler () users ! sourceforge ! net>
Date:       2012-04-17 16:27:26
Message-ID: E1SKBFZ-00023k-Ph () sfs-ml-3 ! v29 ! ch3 ! sourceforge ! com
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The branch "master" has been updated in SBCL:
       via  8105eb908700dfc868cfc00d106981845d954594 (commit)
      from  4d132b6acf722b3cd1672477d6371224f22c9b27 (commit)

- Log -----------------------------------------------------------------
commit 8105eb908700dfc868cfc00d106981845d954594
Author: Lutz Euler <lutz.euler@freenet.de>
Date:   Tue Apr 17 18:26:48 2012 +0200

    Micro-optimize some type tests on x86-64 for code size.
    
    In SIGNED-BYTE-64-P and CHECK-SIGNED-BYTE-64, if possible, spare a REX
    prefix by using a 32-bit instead of a 64-bit register move instruction.
    
    In UNSIGNED-BYTE-64-P and CHECK-UNSIGNED-BYTE-64 use AL instead of RAX
    to test the lowtag.
---
 src/compiler/x86-64/type-vops.lisp |   25 +++++++++++++++----------
 1 files changed, 15 insertions(+), 10 deletions(-)

diff --git a/src/compiler/x86-64/type-vops.lisp b/src/compiler/x86-64/type-vops.lisp
index 47b18d3..12c09af 100644
--- a/src/compiler/x86-64/type-vops.lisp
+++ b/src/compiler/x86-64/type-vops.lisp
@@ -13,6 +13,14 @@
 
 ;;;; test generation utilities
 
+;;; Optimize the case of moving a 64-bit value into RAX when not caring
+;;; about the upper 32 bits: often the REX prefix can be spared.
+(defun move-qword-to-eax (value)
+  (if (and (sc-is value any-reg descriptor-reg)
+           (< (tn-offset value) r8-offset))
+      (move eax-tn (make-dword-tn value))
+      (move rax-tn value)))
+
 (defun generate-fixnum-test (value)
   "zero flag set if VALUE is fixnum"
   (inst test
@@ -72,10 +80,7 @@
   (%test-headers value target not-p nil headers drop-through))
 
 (defun %test-lowtag (value target not-p lowtag)
-  (if (and (sc-is value any-reg descriptor-reg)
-           (< (tn-offset value) r8-offset))
-      (move eax-tn (make-dword-tn value)) ; shorter encoding (no REX prefix)
-      (move rax-tn value))
+  (move-qword-to-eax value)
   (inst and al-tn lowtag-mask)
   (inst cmp al-tn lowtag)
   (inst jmp (if not-p :ne :e) target))
@@ -249,7 +254,7 @@
             (values target not-target))
       (generate-fixnum-test value)
       (inst jmp :e yep)
-      (move rax-tn value)
+      (move-qword-to-eax value)
       (inst and al-tn lowtag-mask)
       (inst cmp al-tn other-pointer-lowtag)
       (inst jmp :ne nope)
@@ -265,7 +270,7 @@
                                      value)))
       (generate-fixnum-test value)
       (inst jmp :e yep)
-      (move rax-tn value)
+      (move-qword-to-eax value)
       (inst and al-tn lowtag-mask)
       (inst cmp al-tn other-pointer-lowtag)
       (inst jmp :ne nope)
@@ -294,8 +299,8 @@
         (inst jmp :e fixnum)
 
         ;; If not, is it an other pointer?
-        (inst and rax-tn lowtag-mask)
-        (inst cmp rax-tn other-pointer-lowtag)
+        (inst and al-tn lowtag-mask)
+        (inst cmp al-tn other-pointer-lowtag)
         (inst jmp :ne nope)
         ;; Get the header.
         (loadw rax-tn value 0 other-pointer-lowtag)
@@ -337,8 +342,8 @@
       (inst jmp :e fixnum)
 
       ;; If not, is it an other pointer?
-      (inst and rax-tn lowtag-mask)
-      (inst cmp rax-tn other-pointer-lowtag)
+      (inst and al-tn lowtag-mask)
+      (inst cmp al-tn other-pointer-lowtag)
       (inst jmp :ne nope)
       ;; Get the header.
       (loadw rax-tn value 0 other-pointer-lowtag)

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