From ff2f362c8eb6da798fdedc6c1b0a23b0331db435 Mon Sep 17 00:00:00 2001
From: Joe Marshall <jmarshall@alum.mit.edu>
Date: Wed, 24 Feb 2010 19:00:11 -0800
Subject: [PATCH] Elide conditional canonicalization.

---
 src/sf/sf.pkg    |  1 +
 src/sf/subst.scm | 32 +++++++++++++++++++++-----------
 2 files changed, 22 insertions(+), 11 deletions(-)

diff --git a/src/sf/sf.pkg b/src/sf/sf.pkg
index 87d055580..faee1fea6 100644
--- a/src/sf/sf.pkg
+++ b/src/sf/sf.pkg
@@ -92,6 +92,7 @@ USA.
   (parent (scode-optimizer))
   (export ()
 	  sf:display-top-level-procedure-names?
+	  sf:enable-elide-conditional-canonicalization?
 	  sf:enable-elide-double-negatives?)
   (export (scode-optimizer)
 	  integrate/top-level
diff --git a/src/sf/subst.scm b/src/sf/subst.scm
index 65838068d..1ecf124ee 100644
--- a/src/sf/subst.scm
+++ b/src/sf/subst.scm
@@ -147,19 +147,29 @@ USA.
 			    (combination/operands combination)))))
 
 ;;;; CONDITIONAL
+
+;; Expression such as (if (pair? x) #t #f) don't need the conditional.
+(define sf:enable-elide-conditional-canonicalization? #t)
+
 (define-method/integrate 'CONDITIONAL
   (lambda (operations environment expression)
-    (conditional/make
-     (conditional/scode expression)
-     (integrate/expression
-      operations environment
-      (conditional/predicate expression))
-     (integrate/expression
-      operations environment
-      (conditional/consequent expression))
-     (integrate/expression
-      operations environment
-      (conditional/alternative expression)))))
+    (let ((ipred (integrate/expression
+		  operations environment
+		  (conditional/predicate expression)))
+	  (icons (integrate/expression
+		  operations environment
+		  (conditional/consequent expression)))
+	  (ialt (integrate/expression
+		 operations environment
+		 (conditional/alternative expression))))
+      (cond ((and (expression/constant-eq? icons #t)
+		  (expression/constant-eq? ialt #f)
+		  (expression/boolean? ipred)
+		  (noisy-test sf:enable-elide-conditional-canonicalization?
+			      "elide conditional canonicalization"))
+	     ipred)
+	    (else
+	     (conditional/make (conditional/scode expression) ipred icons ialt))))))
 
 ;;; CONSTANT
 (define-method/integrate 'CONSTANT
-- 
2.25.1