From 3df95385bcc5294a212534d0991f1ffef1454aca Mon Sep 17 00:00:00 2001
From: Ori Bernstein <ori@eigenstate.org'>
Date: Thu, 27 Feb 2020 15:09:10 -0500
Subject: [PATCH] fix special case for null pointer constants in cond
 expressions

	Section 6.5.15 of the C99 spec requires that if
	one argument of a ?: expression is a null pointer
	constant, and the other has a pointer type T*, then
	the type of the expression is T*.

	We were attempting to follow this rule, however,
	we only handled literal expressions when checking
	for null pointers.

	This change looks through casts, so 'nil' and 'NULL',
	and their expansion '(void*)0' are all detected as
	null pointer constants.
---
 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 87aceb598..f22cad7e3 100644
--- a/sys/src/cmd/cc/cc.h
+++ b/sys/src/cmd/cc/cc.h
@@ -691,6 +691,7 @@ 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 418bbae26..49fcefd1a 100644
--- a/sys/src/cmd/cc/com.c
+++ b/sys/src/cmd/cc/com.c
@@ -341,11 +341,13 @@ 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 ee4ab07ce..9be762a0c 100644
--- a/sys/src/cmd/cc/sub.c
+++ b/sys/src/cmd/cc/sub.c
@@ -1025,6 +1025,21 @@ loop:
 	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)
 {