From 92c59818b538ae7ca4973b5e0bafa8b7efadcb78 Mon Sep 17 00:00:00 2001
From: Michael Forney <mforney@mforney.org>
Date: Fri, 22 Mar 2024 01:50:07 -0700
Subject: Implement C23 nullptr constant

---
 cc.h             |  4 +++-
 expr.c           | 15 +++++++++++++--
 test/nullptr.c   |  4 ++++
 test/nullptr.qbe |  3 +++
 type.c           |  2 ++
 5 files changed, 25 insertions(+), 3 deletions(-)
 create mode 100644 test/nullptr.c
 create mode 100644 test/nullptr.qbe

diff --git a/cc.h b/cc.h
index 51b7cdc..bd05deb 100644
--- a/cc.h
+++ b/cc.h
@@ -166,7 +166,8 @@ enum typekind {
 	TYPEARRAY,
 	TYPEFUNC,
 	TYPESTRUCT,
-	TYPEUNION
+	TYPEUNION,
+	TYPENULLPTR,
 };
 
 enum typeprop {
@@ -446,6 +447,7 @@ extern struct type typeint, typeuint;
 extern struct type typelong, typeulong;
 extern struct type typellong, typeullong;
 extern struct type typefloat, typedouble, typeldouble;
+extern struct type typenullptr;
 extern struct type *typeadjvalist;
 
 /* targ */
diff --git a/expr.c b/expr.c
index 1e94f68..20b943e 100644
--- a/expr.c
+++ b/expr.c
@@ -175,6 +175,8 @@ nullpointer(struct expr *e)
 {
 	if (e->kind != EXPRCONST)
 		return false;
+	if (e->type->kind == TYPENULLPTR)
+		return true;
 	if (!(e->type->prop & PROPINT) && (e->type->kind != TYPEPOINTER || e->type->base != &typevoid))
 		return false;
 	return e->u.constant.u == 0;
@@ -188,8 +190,8 @@ exprassign(struct expr *e, struct type *t)
 	et = e->type;
 	switch (t->kind) {
 	case TYPEBOOL:
-		if (!(et->prop & PROPARITH) && et->kind != TYPEPOINTER)
-			error(&tok.loc, "assignment to bool must be from arithmetic or pointer type");
+		if (!(et->prop & PROPARITH) && et->kind != TYPEPOINTER && et->kind != TYPENULLPTR)
+			error(&tok.loc, "assignment to bool must be from arithmetic, pointer, or nullptr_t type");
 		break;
 	case TYPEPOINTER:
 		if (nullpointer(e))
@@ -201,6 +203,10 @@ exprassign(struct expr *e, struct type *t)
 		if ((et->qual & t->qual) != et->qual)
 			error(&tok.loc, "assignment to pointer discards qualifiers");
 		break;
+	case TYPENULLPTR:
+		if (!nullpointer(e))
+			error(&tok.loc, "assignment to nullptr_t must be from null pointer constant or expression with type nullptr_t");
+		break;
 	case TYPESTRUCT:
 	case TYPEUNION:
 		if (!typecompatible(t, et))
@@ -699,6 +705,11 @@ primaryexpr(struct scope *s)
 		e->u.constant.u = tok.kind == TTRUE;
 		next();
 		break;
+	case TNULLPTR:
+		e = mkexpr(EXPRCONST, &typenullptr, NULL);
+		e->u.constant.u = 0;
+		next();
+		break;
 	case TLPAREN:
 		next();
 		e = expr(s);
diff --git a/test/nullptr.c b/test/nullptr.c
new file mode 100644
index 0000000..8f5b436
--- /dev/null
+++ b/test/nullptr.c
@@ -0,0 +1,4 @@
+typeof(nullptr) x = 0;
+_Static_assert(sizeof x == sizeof(char *));
+int *y = nullptr;
+bool z = nullptr;
diff --git a/test/nullptr.qbe b/test/nullptr.qbe
new file mode 100644
index 0000000..c805942
--- /dev/null
+++ b/test/nullptr.qbe
@@ -0,0 +1,3 @@
+export data $x = align 8 { l 0, }
+export data $y = align 8 { l 0, }
+export data $z = align 1 { b 0, }
diff --git a/type.c b/type.c
index 02e9a82..5f6e417 100644
--- a/type.c
+++ b/type.c
@@ -39,6 +39,8 @@ struct type typefloat   = FLTTYPE(TYPEFLOAT, 4);
 struct type typedouble  = FLTTYPE(TYPEDOUBLE, 8);
 struct type typeldouble = FLTTYPE(TYPELDOUBLE, 16);
 
+struct type typenullptr = {.kind = TYPENULLPTR, .size = 8, .align = 8, .prop = PROPSCALAR};
+
 struct type *typeadjvalist;
 
 struct type *
-- 
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