From: Paul Khuong <pvk@pvk.ca>
Date: Fri, 7 Jun 2013 23:06:32 +0000 (-0400)
Subject: More associativity-based constant-folding
X-Git-Url: http://repo.macrolet.net/gitweb/?a=commitdiff_plain;h=e4f3dfe7fefc2ab3980360ce597dc378c6b02393;p=sbcl.git

More associativity-based constant-folding

 Detect patterns like (+ (- x k1) k2) and (* (/ x k1) k2).
---

diff --git a/src/compiler/srctran.lisp b/src/compiler/srctran.lisp
index c1aa106..d408fa3 100644
--- a/src/compiler/srctran.lisp
+++ b/src/compiler/srctran.lisp
@@ -3444,13 +3444,17 @@
                   (splice-fun-args x ',folded 2)
                   `(lambda (x y z)
                      (declare (ignore y z))
-                     (,',operator x ',(,folded y (lvar-value z))))))))
+                     ;; (operator (folded x y) z)
+                     ;; == (operator x (folded z y))
+                     (,',operator x ',(,folded (lvar-value z) y)))))))
   (def logand)
   (def logior)
   (def logxor)
   (def logtest :folded logand)
   (def + :type rational)
-  (def * :type rational))
+  (def + :type rational :folded -)
+  (def * :type rational)
+  (def * :type rational :folded /))
 
 (deftransform mask-signed-field ((width x) ((constant-arg unsigned-byte) *))
   "Fold mask-signed-field/mask-signed-field of constant width"