From: Juho Snellman <jsnell@iki.fi>
Date: Sun, 16 Jul 2006 06:42:11 +0000 (+0000)
Subject: 0.9.14.17:
X-Git-Url: http://repo.macrolet.net/gitweb/?a=commitdiff_plain;h=10e203ce6b6846114f93ea83ab2451ee7c640269;p=sbcl.git

0.9.14.17:
	Implement x86-64 MOVE-FROM-SIGNED overflow detection using IMUL
        instead of using three separate shifts / checks, which is somewhat
        faster and smaller.
---

diff --git a/src/compiler/x86-64/move.lisp b/src/compiler/x86-64/move.lisp
index a9a7ec5..cc24df4 100644
--- a/src/compiler/x86-64/move.lisp
+++ b/src/compiler/x86-64/move.lisp
@@ -280,11 +280,15 @@
      (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 8)
        (inst jmp :o bignum)
        (emit-label done)
 
diff --git a/version.lisp-expr b/version.lisp-expr
index e62d17e..c7dd53a 100644
--- a/version.lisp-expr
+++ b/version.lisp-expr
@@ -17,4 +17,4 @@
 ;;; checkins which aren't released. (And occasionally for internal
 ;;; versions, especially for internal versions off the main CVS
 ;;; branch, it gets hairier, e.g. "0.pre7.14.flaky4.13".)
-"0.9.14.16"
+"0.9.14.17"