PR c/39582

	* c-typeck.c (c_expr_sizeof_type): Create a C_MAYBE_CONST_EXPR
	with non-null C_MAYBE_CONST_EXPR_PRE if size of a variable-length
	type is an integer constant.

testsuite:
	* gcc.dg/vla-20.c: New test.


git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@146787 138bc75d-0d04-0410-961f-82ee72b054a4

1 files changed, 12 insertions, 2 deletions

diff --git a/gcc/c-typeck.c b/gcc/c-typeck.c
index 1cfab1f14f2..dc7d731ee02 100644
--- a/gcc/c-typeck.c
+++ b/gcc/c-typeck.c
@@ -2391,8 +2391,18 @@ c_expr_sizeof_type (struct c_type_name *t)
   ret.value = c_sizeof (type);
   ret.original_code = ERROR_MARK;
   ret.original_type = NULL;
-  if (type_expr && c_vla_type_p (type))
-    {
+  if ((type_expr || TREE_CODE (ret.value) == INTEGER_CST)
+      && c_vla_type_p (type))
+    {
+      /* If the type is a [*] array, it is a VLA but is represented as
+	 having a size of zero.  In such a case we must ensure that
+	 the result of sizeof does not get folded to a constant by
+	 c_fully_fold, because if the size is evaluated the result is
+	 not constant and so constraints on zero or negative size
+	 arrays must not be applied when this sizeof call is inside
+	 another array declarator.  */
+      if (!type_expr)
+	type_expr = integer_zero_node;
       ret.value = build2 (C_MAYBE_CONST_EXPR, TREE_TYPE (ret.value),
 			  type_expr, ret.value);
       C_MAYBE_CONST_EXPR_NON_CONST (ret.value) = !type_expr_const;