From 8b46fab07665dceecc0fd075eefa48f5af3f7285 Mon Sep 17 00:00:00 2001
From: lufia <lufia@lufia.org>
Date: Sat, 26 Jul 2025 00:11:02 +0900
Subject: [PATCH] sys/src/cmd/cc: fix special case for null pointer constants
 in cond expressions

ref https://github.com/9front/9front/commit/3df95385bcc5294a212534d0991f1ffef1454aca
---
 sys/src/cmd/cc/cc.h  |  1 +
 sys/src/cmd/cc/com.c |  6 ++++--
 sys/src/cmd/cc/sub.c | 15 +++++++++++++++
 3 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/sys/src/cmd/cc/cc.h b/sys/src/cmd/cc/cc.h
index 8445a868..a7d5c59d 100644
--- a/sys/src/cmd/cc/cc.h
+++ b/sys/src/cmd/cc/cc.h
@@ -694,6 +694,7 @@ Type*	copytyp(Type*);
 void	typeext(Type*, Node*);
 void	typeext1(Type*, Node*);
 int	side(Node*);
+int	zpconst(Node*);
 int	vconst(Node*);
 int	log2(uvlong);
 int	vlog(Node*);
diff --git a/sys/src/cmd/cc/com.c b/sys/src/cmd/cc/com.c
index fab1ba63..996d96c9 100644
--- a/sys/src/cmd/cc/com.c
+++ b/sys/src/cmd/cc/com.c
@@ -331,11 +331,13 @@ tcomo(Node *n, int f)
 		o |= tcom(r->left);
 		if(o | tcom(r->right))
 			goto bad;
-		if(r->right->type->etype == TIND && vconst(r->left) == 0) {
+		if(r->right->type->etype == TIND && zpconst(r->left)) {
+			r->type = r->right->type;
 			r->left->type = r->right->type;
 			r->left->vconst = 0;
 		}
-		if(r->left->type->etype == TIND && vconst(r->right) == 0) {
+		if(r->left->type->etype == TIND && zpconst(r->right)) {
+			r->type = r->left->type;
 			r->right->type = r->left->type;
 			r->right->vconst = 0;
 		}
diff --git a/sys/src/cmd/cc/sub.c b/sys/src/cmd/cc/sub.c
index e5a5cf44..5190c17e 100644
--- a/sys/src/cmd/cc/sub.c
+++ b/sys/src/cmd/cc/sub.c
@@ -987,6 +987,21 @@ side(Node *n)
 	return 1;
 }
 
+int
+zpconst(Node *n)
+{
+	while(n->op == OCAST){
+		if(n->type == T)
+			break;
+		if(n->type->etype != TIND)
+			break;
+		if(n->type->link->etype != TVOID)
+			break;
+		n = n->left;
+	}
+	return vconst(n) == 0;
+}
+
 int
 vconst(Node *n)
 {