From 5e8fa7f8d40eed6218ae39886181eff0140059b3 Mon Sep 17 00:00:00 2001
From: Kaz Kylheku <kaz@kylheku.com>
Date: Sat, 27 Feb 2021 12:17:46 -0800
Subject: compiler: optimize useless if to jmp.

* share/txr/stdlib/optimize.tl (basic-blocks
thread-jumps-block): This is a complementary optimization to
the one which  matches (if (d @reg) @jlabel). An if
instruction conditional on the nil register (t 0) is always
taken, and can be rewritten to a jmp. This can promote
elimination of dead code.
---
 share/txr/stdlib/optimize.tl | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/share/txr/stdlib/optimize.tl b/share/txr/stdlib/optimize.tl
index 259a64ae..81536c32 100644
--- a/share/txr/stdlib/optimize.tl
+++ b/share/txr/stdlib/optimize.tl
@@ -258,6 +258,8 @@
       (set insn ninsn
            ninsn (match-case insn
                    ((if (d @reg) @jlabel) nil)
+                   ((if (t 0) @jlabel)
+                    ^(jmp ,jlabel))
                    ((jmp @jlabel)
                     (let ((jinsns [bb.hash jlabel].insns))
                       (match-case jinsns
-- 
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