From 82ffd40592ee8a32c41dae6d3ca423592166271e Mon Sep 17 00:00:00 2001
From: Gustavo Massaccesi <gustavo@oma.org.ar>
Date: Mon, 7 Jul 2014 19:55:13 -0300
Subject: [PATCH] optimizer: transform (if v x v) to (if v x #f)

---
 .../racket-test/tests/racket/optimize.rktl    | 26 ++++++++++++++++++-
 racket/src/racket/src/optimize.c              | 19 +++++++++-----
 2 files changed, 38 insertions(+), 7 deletions(-)

diff --git a/pkgs/racket-pkgs/racket-test/tests/racket/optimize.rktl b/pkgs/racket-pkgs/racket-test/tests/racket/optimize.rktl
index 9e562de543..112a6ef69e 100644
--- a/pkgs/racket-pkgs/racket-test/tests/racket/optimize.rktl
+++ b/pkgs/racket-pkgs/racket-test/tests/racket/optimize.rktl
@@ -1361,10 +1361,34 @@
                               (if r r (something-else)))
                             (a1)
                             (a2)))
-           '(lambda (x)  (if (if (something) #t (something-else))
+           '(lambda (x) (if (if (something) #t (something-else))
+                            (a1)
+                            (a2))))
+
+(test-comp '(lambda (x) (if (if x x (something-else))
+                            (a1)
+                            (a2)))
+           '(lambda (x) (if (if x #t (something-else))
                              (a1)
                              (a2))))
 
+(test-comp '(lambda (x) (if x (something-else) x))
+           '(lambda (x) (if x (something-else) #f)))
+                             
+(test-comp '(lambda (x) (if (if x #t #f)
+                            (a1)
+                            (a2)))
+           '(lambda (x) (if x
+                            (a1)
+                            (a2))))
+
+(test-comp '(lambda (x) (if (if x x x)
+                            (a1)
+                            (a2)))
+           '(lambda (x) (if x
+                            (a1)
+                            (a2))))
+
 (test-comp '(if (let ([z (random)]) null) 1 2)
            '(if (let ([z (random)]) #t) 1 2))
 
diff --git a/racket/src/racket/src/optimize.c b/racket/src/racket/src/optimize.c
index ec2d890598..5c35f3c0c2 100644
--- a/racket/src/racket/src/optimize.c
+++ b/racket/src/racket/src/optimize.c
@@ -3620,17 +3620,24 @@ static Scheme_Object *optimize_branch(Scheme_Object *o, Optimize_Info *info, int
   tb = b->tbranch;
   fb = b->fbranch;
 
+  /* Convert (if <id> expr <id>) to (if <id> expr #f) */
+  if (SAME_TYPE(SCHEME_TYPE(t), scheme_local_type)
+      && SAME_TYPE(SCHEME_TYPE(fb), scheme_local_type)
+      && (SCHEME_LOCAL_POS(t) == SCHEME_LOCAL_POS(fb))) {
+    fb = scheme_false;
+  }
+  
   if (context & OPT_CONTEXT_BOOLEAN) {
-    /* For test position, convert (if <expr> #t #f) to <expr> */
-    if (SAME_OBJ(tb, scheme_true) && SAME_OBJ(fb, scheme_false))
-      return scheme_optimize_expr(t, info, context);
-
-    /* Convert (if <id> <id> expr) to (if <id> #t expr) */
+    /* For test position, convert (if <id> <id> expr) to (if <id> #t expr) */
     if (SAME_TYPE(SCHEME_TYPE(t), scheme_local_type)
         && SAME_TYPE(SCHEME_TYPE(tb), scheme_local_type)
         && (SCHEME_LOCAL_POS(t) == SCHEME_LOCAL_POS(tb))) {
-      b->tbranch = tb = scheme_true;
+      tb = scheme_true;
     }
+
+    /* Convert (if <expr> #t #f) to <expr> */
+    if (SAME_OBJ(tb, scheme_true) && SAME_OBJ(fb, scheme_false))
+      return scheme_optimize_expr(t, info, context);
   }
 
   optimize_info_seq_init(info, &info_seq);