From: Olof-Joachim Frahm <olof@macrolet.net>
Date: Thu, 7 Nov 2013 00:07:33 +0000 (+0100)
Subject: Implement LOGCOUNT via POPCNT instruction.
X-Git-Url: http://repo.macrolet.net/gitweb/?a=commitdiff_plain;h=b16bb7d562abe06cd111e8e42ec56498b437a413;p=sbcl.git

Implement LOGCOUNT via POPCNT instruction.
---

diff --git a/src/compiler/x86-64/arith.lisp b/src/compiler/x86-64/arith.lisp
index f455bff..1026743 100644
--- a/src/compiler/x86-64/arith.lisp
+++ b/src/compiler/x86-64/arith.lisp
@@ -1197,6 +1197,20 @@ constant shift greater than word length")))
     (inst mov mask #x0101010101010101)
     (inst imul result mask)
     (inst shr result 56)))
+
+;; only marginally faster then the regular one, but shorter
+;; might be unavailable though
+(define-vop (unsigned-byte-64-count/popcnt)
+  (:translate logcount)
+  (:note "inline (unsigned-byte 64) logcount using popcnt instruction")
+  (:policy :fast-safe)
+  (:guard (member :popcnt *backend-subfeatures*))
+  (:args (arg :scs (unsigned-reg) :target result))
+  (:arg-types unsigned-num)
+  (:results (result :scs (unsigned-reg)))
+  (:result-types positive-fixnum)
+  (:generator 1
+    (inst popcnt arg result)))
 
 ;;;; binary conditional VOPs