More identity folding for LOGAND and LOGIOR with constants

[sbcl.git] / src / compiler / srctran.lisp

diff --git a/src/compiler/srctran.lisp b/src/compiler/srctran.lisp
index d408fa3..7c7f8fd 100644 (file)
--- a/src/compiler/srctran.lisp
+++ b/src/compiler/srctran.lisp
@@ -3401,14 +3401,17 @@
   (def logxor -1 (lognot x))
   (def logxor 0 x))
 
+(defun least-zero-bit (x)
+  (and (/= x -1)
+       (1- (integer-length (logxor x (1+ x))))))
+
 (deftransform logand ((x y) (* (constant-arg t)) *)
   "fold identity operation"
-  (let ((y (lvar-value y)))
-    (unless (and (plusp y)
-                 (= y (1- (ash 1 (integer-length y)))))
-      (give-up-ir1-transform))
-    (unless (csubtypep (lvar-type x)
-                       (specifier-type `(integer 0 ,y)))
+  (let* ((y (lvar-value y))
+         (width (or (least-zero-bit y) '*)))
+    (unless (and (neq width 0) ; (logand x 0) handled elsewhere
+                 (csubtypep (lvar-type x)
+                            (specifier-type `(unsigned-byte ,width))))
       (give-up-ir1-transform))
     'x))
 
@@ -3419,6 +3422,16 @@
       (give-up-ir1-transform))
     'x))
 
+(deftransform logior ((x y) (* (constant-arg t)) *)
+  "fold identity operation"
+  (let* ((y (lvar-value y))
+         (width (or (least-zero-bit (lognot y))
+                    (give-up-ir1-transform)))) ; (logior x 0) handled elsewhere
+    (unless (csubtypep (lvar-type x)
+                       (specifier-type `(integer ,(- (ash 1 width)) -1)))
+      (give-up-ir1-transform))
+    'x))
+
 ;;; Pick off easy association opportunities for constant folding.
 ;;; More complicated stuff that also depends on commutativity
 ;;; (e.g. (f (f x k1) (f y k2)) => (f (f x y) (f k1 k2))) should