From a4e89a91bff4de065b138a6fa4183cb4234d42c2 Mon Sep 17 00:00:00 2001
From: Kaz Kylheku <kaz@kylheku.com>
Date: Mon, 17 Apr 2023 16:46:10 -0700
Subject: compiler: rewrite t-regs through defining instruction.

* stdlib/optimize.tl (subst-preserve): Rename list param
to insn for clarity.
(careful-subst-preserve): New function. This is like
subst-preserve, but used only for instructions that
have destination registers. It performs a rewrite
such that those destination positions are avoided.
(basic-blocks rename): When the instruction has src
or dst as a target, don't just stop before that
insn. Do the substitution in the source operands using
careful-subst-preserve.
---
 stdlib/optimize.tl | 30 ++++++++++++++++++++++++------
 1 file changed, 24 insertions(+), 6 deletions(-)

diff --git a/stdlib/optimize.tl b/stdlib/optimize.tl
index e78c9300..f3e2a6c6 100644
--- a/stdlib/optimize.tl
+++ b/stdlib/optimize.tl
@@ -354,10 +354,25 @@
       ((nequal ninsn oinsn) (append (ldiff code tail) (list ninsn)))
       (t code))))
 
-(defun subst-preserve (x y bb li list)
-  (let ((sub (subst x y list)))
+(defun subst-preserve (x y bb li insn)
+  (let ((sub (subst x y insn)))
     (cond
-      ((equal sub list) list)
+      ((equal sub insn) insn)
+      (t (set [bb.li-hash sub] li) sub))))
+
+(defun careful-subst-preserve (x y bb li insn)
+  (let ((sub (match-case insn
+               ((@(or apply call) @def . @refs)
+                ^(,(car insn) ,def ,*(subst x y refs)))
+               ((@(or gapply gcall) @def @fn . @refs)
+                ^(,(car insn) ,def ,fn ,*(subst x y refs)))
+               ((mov @def @x)
+                ^(mov ,def ,y))
+               ((catch @esreg @eareg . @refs)
+                ^(catch ,esreg ,eareg ,*(subst x y refs)))
+               (@else else))))
+    (cond
+      ((equal sub insn) insn)
       (t (set [bb.li-hash sub] li) sub))))
 
 (defmeth basic-blocks rename (bb insns dst src)
@@ -369,12 +384,15 @@
               (li [bb.li-hash insn]))
           (cond
             (close (add insn))
-            ((or (and vreg end)
-                 (mequal li.def0 dst src)
-                 (mequal li.def1 dst src))
+            ((and vreg end)
              (add insn)
              (pend insns)
              (set insns nil))
+            ((or (mequal dst li.def0 li.def1)
+                 (mequal src li.def0 li.def1))
+             (add (careful-subst-preserve dst src bb li insn))
+             (pend insns)
+             (set insns nil))
             (t (add (subst-preserve dst src bb li insn)))))))))
 
 (defmeth basic-blocks peephole-block (bb bl)
-- 
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