From cf126a147c108497ef8a387dc869a4c24a9622ed Mon Sep 17 00:00:00 2001
From: Kaz Kylheku <kaz@kylheku.com>
Date: Wed, 3 Mar 2021 21:10:14 -0800
Subject: compiler: another late-peephole pattern.

* share/txr/stdlib/optimize.tl (late-peephole): Add a
6-instruction pattern which is seen in pattern-matching code
in optimize.tlo and compiler.tlo. This can be tidied up a
little bit, reducing the instructions to 5, eliminating
redundant comparisons and threading a jump. At this point we
are probably working too hard for too little gain.  More
effort in other areas like common subexpression elimination
could produce bigger wins.
---
 share/txr/stdlib/optimize.tl | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/share/txr/stdlib/optimize.tl b/share/txr/stdlib/optimize.tl
index 1541cd17..df423f2f 100644
--- a/share/txr/stdlib/optimize.tl
+++ b/share/txr/stdlib/optimize.tl
@@ -504,6 +504,27 @@
          ^((ifq ,reg (t 0) ,lab3)
            ,lab1
            ,*rest))))
+    (((mov (t @tn) (d @dn))
+      (jmp @lab3)
+      @lab1
+      (mov (t @tn) (t 0))
+      (jmp @lab3)
+      @lab2
+      (mov (t @tn) (t 0))
+      @(symbolp @lab3)
+      (ifq (t @tn) (t 0) @lab4)
+      . @rest)
+     (let ((lab5 (gensym "nl")))
+       ^((mov (t ,tn) (d ,dn))
+         (jmp ,lab4)
+         ,lab1
+         ,lab2
+         (mov (t ,tn) (t 0))
+         (jmp ,lab5)
+         ,lab3
+         (ifq (t ,tn) (t 0) ,lab4)
+         ,lab5
+         ,*rest)))
     (@else else)))
 
 (defun rewrite (fun list)
-- 
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