From 87dc3ea290a4ba75f153c5bb8b9fb87ec548e64f Mon Sep 17 00:00:00 2001
From: Quentin Carbonneaux <quentin@c9x.me>
Date: Mon, 21 Nov 2022 14:08:08 +0100
Subject: [PATCH] fix allocation ordering bug in rega

When we process one block, we
start by allocating registers
for all the temporaries live
at the exit of the block.

Before this patch we processed
temps first, then in doblk() we
would mark globally live registers
allocated. This meant that temps
could get wrongly assigned a live
register.

The fix is simple: we now process
registers first at block exits,
then allocate temps.
---
 rega.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/rega.c b/rega.c
index dd77a75..c97d1e1 100644
--- a/rega.c
+++ b/rega.c
@@ -359,8 +359,6 @@ doblk(Blk *b, RMap *cur)
 	Mem *m;
 	Ref *ra[4];
 
-	for (r=0; bsiter(b->out, &r) && r<Tmp0; r++)
-		radd(cur, r, r);
 	if (rtype(b->jmp.arg) == RTmp)
 		b->jmp.arg = ralloc(cur, b->jmp.arg.val);
 	curi = &insb[NIns];
@@ -534,6 +532,8 @@ rega(Fn *fn)
 				rl[j] = t;
 			}
 		}
+		for (r=0; bsiter(b->out, &r) && r<Tmp0; r++)
+			radd(&cur, r, r);
 		for (j=0; j<x; j++)
 			ralloctry(&cur, rl[j], 1);
 		for (j=0; j<x; j++)