[cmucl-commit] [git] CMU Common Lisp branch master updated. snapshot-2013-02-6-ga31494b

[Raymond Toy]

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- Log -----------------------------------------------------------------
commit a31494bd9cb9c857903937cc2a5b310aa1184895
Author: Raymond Toy <toy.raymond at gmail.com>
Date:   Mon Feb 18 19:54:07 2013 -0800

    Optimize shifts that are known to be right shifts.
    
    Without this, the general shift vop is used which has to test for the
    sign of the shift before shifting.  This micro-optimization removes
    the test when we know the sign of the shift.

diff --git a/src/compiler/x86/arith.lisp b/src/compiler/x86/arith.lisp
index 6739f9b..37fc816 100644
--- a/src/compiler/x86/arith.lisp
+++ b/src/compiler/x86/arith.lisp
@@ -1713,3 +1713,115 @@
     (cut-to-width integer width)
     'vm::ash-left-mod32))
 )
+
+(in-package :x86)
+
+(defknown ash-right-signed ((signed-byte #.vm:word-bits)
+			    (and fixnum unsigned-byte))
+  (signed-byte #.vm:word-bits)
+  (movable foldable flushable))
+
+(defknown ash-right-unsigned ((unsigned-byte #.vm:word-bits)
+			      (and fixnum unsigned-byte))
+  (unsigned-byte #.vm:word-bits)
+  (movable foldable flushable))
+
+(macrolet
+    ((frob (trans name sc-type type shift-inst cost)
+       `(define-vop (,name)
+	  (:note _N"inline right ASH")
+	  (:translate ,trans)
+	  (:args (number :scs (,sc-type))
+		 (amount :scs (signed-reg unsigned-reg immediate)))
+	  (:arg-types ,type positive-fixnum)
+	  (:results (result :scs (,sc-type)))
+	  (:result-types ,type)
+	  (:policy :fast-safe)
+	  (:temporary (:sc unsigned-reg :offset ecx-offset) cl)
+	  (:generator ,cost
+	    (sc-case amount
+	      ((signed-reg unsigned-reg)
+	       (move cl amount)
+	       (move result number)
+	       (inst ,shift-inst result :cl))
+	      (immediate
+	       (let ((amt (tn-value amount)))
+		 (move result number)
+		 (inst ,shift-inst result amt))))))))
+  (frob ash-right-signed fast-ash-right/signed=>signed
+	signed-reg signed-num sar 4)
+  (frob ash-right-unsigned fast-ash-right/unsigned=>unsigned
+	unsigned-reg unsigned-num shr 4))
+
+;; Constant right shift.
+(macrolet
+    ((frob (trans name sc-type type shift-inst cost max-shift)
+       `(define-vop (,name)
+	  (:note _N"inline right ASH")
+	  (:translate ,trans)
+	  (:args (number :target result :scs (,sc-type)))
+	  (:info amount)
+	  (:arg-types ,type
+		      (:constant (integer 0 ,max-shift)))
+	  (:results (result :scs (,sc-type)))
+	  (:result-types ,type)
+	  (:policy :fast-safe)
+	  (:generator 4
+	    (cond ((zerop amount)
+		   (move result number))
+		  (t
+		   (move result number)
+		   (inst ,shift-inst result amount)))))))
+  (frob ash-right-signed fast-ash-right-c/signed=>signed
+	signed-reg signed-num sar 1 31)
+  (frob ash-right-unsigned fast-ash-right-c/unsigned=>unsigned
+	unsigned-reg unsigned-num shr 1 31))
+
+;; FIXME: The following stuff for right shifts should be moved to
+;; vm-tran (or somewhere common), once we make it the same on sparc
+;; and ppc.
+
+;; Need these so constant folding works with the deftransform.
+
+(defun ash-right-signed (num shift)
+  (declare (type (signed-byte #.vm:word-bits) num)
+	   (type (integer 0 #.(1- vm:word-bits)) shift))
+  (ash num (- shift)))
+
+(defun ash-right-unsigned (num shift)
+  (declare (type (unsigned-byte #.vm:word-bits) num)
+	   (type (integer 0 #.(1- vm:word-bits)) shift))
+  (ash num (- shift)))
+
+;; If we can prove that we have a right shift, just do the right shift
+;; instead of calling the inline ASH which has to check for the
+;; direction of the shift at run-time.
+(in-package "C")
+
+(deftransform ash ((num shift) (integer integer))
+  (let ((num-type (continuation-type num))
+	(shift-type (continuation-type shift)))
+    ;; Can only handle right shifts
+    (unless (csubtypep shift-type (specifier-type '(integer * 0)))
+      (give-up))
+
+    ;; If we can prove the shift is so large that all bits are shifted
+    ;; out, return the appropriate constant.  If the shift is small
+    ;; enough, call the VOP.  Otherwise, check for the shift size and
+    ;; do the appropriate thing.  (Hmm, could we just leave the IF
+    ;; s-expr and depend on other parts of the compiler to delete the
+    ;; unreachable parts, if any?)
+    (cond ((csubtypep num-type (specifier-type '(signed-byte #.vm:word-bits)))
+	   ;; A right shift by 31 is the same as a right shift by
+	   ;; larger amount.  We get just the sign.
+	   (if (csubtypep shift-type (specifier-type '(integer #.(- 1 vm:word-bits) 0)))
+	       `(vm::ash-right-signed num (- shift))
+	       `(vm::ash-right-signed num (min (- shift) #.(1- vm:word-bits)))))
+	  ((csubtypep num-type (specifier-type '(unsigned-byte #.vm:word-bits)))
+	   (if (csubtypep shift-type (specifier-type '(integer #.(- 1 vm:word-bits) 0)))
+	       `(vm::ash-right-unsigned num (- shift))
+	       `(if (<= shift #.(- vm:word-bits))
+		 0
+		 (vm::ash-right-unsigned num (- shift)))))
+	  (t
+	   (give-up)))))

-----------------------------------------------------------------------

Summary of changes:
 src/compiler/x86/arith.lisp |  112 +++++++++++++++++++++++++++++++++++++++++++
 1 files changed, 112 insertions(+), 0 deletions(-)


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