expression, evaluate: support compound literals as address constants

RFC PATCH Superseded Nicolai Stange 1 participant 1 message Jul 22, 2015 Sparse checker

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Nicolai Stange

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2015-07-22 23:23 UTC #0 lore raw

RFC PATCH 12/13 expression, evaluate: support compound literals as address constants

Toplevel compound literals have got static storage duration [6.5.2.5(6)].

This implies that
1. their addresses are address constants [6.6(9)] and
2. their initializers must contain constant expressions only [6.5.2.5(3), 6.7.8(4)] .

Flag the anonymous symbol created at expression parsing time as having static storage duration if the compound literal occurs at top level scope.

Flag the whole expression as being an address constant at evaluation time if its corresponding anonymous symbol had been previously marked as having static storage duration.

Signed-off-by Nicolai Stange <[email protected]>

---
 evaluate.c                              |  3 +++
 expression.c                            |  2 ++
 validation/constexpr-compound-literal.c | 18 ++++++++++++++++++
 3 files changed, 23 insertions(+)
 create mode 100644 validation/constexpr-compound-literal.c

evaluate.c +3 -0

index ee5f18f..be239ab 100644
@@ -2769,6 +2769,9 @@ static struct symbol *evaluate_cast(struct expression *expr)
 
 		addr->ctype = &lazy_ptr_ctype;	/* Lazy eval */
 		addr->symbol = sym;
+		if (sym->ctype.modifiers & MOD_TOPLEVEL)
+			addr->flags |=
+				expr_set_flag_mask(EXPR_FLAG_ADDR_CONST_EXPR);
 
 		expr->type = EXPR_PREOP;
 		expr->op = '*';

expression.c +2 -0

index a4b6fa2..4c5cafa 100644
@@ -715,6 +715,8 @@ static struct token *cast_expression(struct token *token, struct expression **tr
 			cast->cast_type = sym;
 			token = expect(token, ')', "at end of cast operator");
 			if (match_op(token, '{')) {
+				if (toplevel(block_scope))
+					sym->ctype.modifiers |= MOD_TOPLEVEL;
 				if (is_force)
 					warning(sym->pos,
 						"[force] in compound literal");

validation/constexpr-compound-literal.c new file +18 -0

new file mode 100644
index 0000000..6019a18
@@ -0,0 +1,18 @@
+static int *a = &(int){ 1 };	// OK
+static int *b = &(int){ *a };	// KO
+
+static void foo(void)
+{
+	int *b = &(int){ 1 };		// OK
+	int *c = &(int){ *a };		// OK
+	static int *d = &(int){ 1 };	// KO
+}
+
+/*
+ * check-name: compound literal address constness verification
+ *
+ * check-error-start
+constexpr-compound-literal.c:2:25: warning: initializer for static storage duration object is not a constant expression
+constexpr-compound-literal.c:8:27: warning: initializer for static storage duration object is not a constant expression
+ * check-error-end
+ */

Signature · 1 line

2.4.5