c++: Fix up build_zero_init_1 once more [PR99106]

My earlier build_zero_init_1 patch for flexible array members created
an empty CONSTRUCTOR.  As the following testcase shows, that doesn't work
very well because the middle-end doesn't expect CONSTRUCTOR elements with
incomplete type (that the empty CONSTRUCTOR at the end of outer CONSTRUCTOR
had).

The following patch just doesn't add any CONSTRUCTOR for the flexible array
members, it doesn't seem to be needed.

2021-02-17  Jakub Jelinek  <jakub@redhat.com>

	PR sanitizer/99106
	* init.c (build_zero_init_1): For flexible array members just return
	NULL_TREE instead of returning empty CONSTRUCTOR with non-complete
	ARRAY_TYPE.

	* g++.dg/ubsan/pr99106.C: New test.

diff --git a/gcc/cp/init.c b/gcc/cp/init.c
index 49950d405216ab2ae986d6443e108eea90275a6f..7d598f6196de0c98304f1a831224993119424615 100644 (file)
--- a/gcc/cp/init.c
+++ b/gcc/cp/init.c
@@ -252,7 +252,7 @@ build_zero_init_1 (tree type, tree nelts, bool static_storage_p,
                                     build_one_cst (TREE_TYPE (nelts)));
       /* Treat flexible array members like [0] arrays.  */
       else if (TYPE_DOMAIN (type) == NULL_TREE)
-       max_index = build_minus_one_cst (sizetype);
+       return NULL_TREE;
       else
        max_index = array_type_nelts (type);
 

diff --git a/gcc/testsuite/g++.dg/ubsan/pr99106.C b/gcc/testsuite/g++.dg/ubsan/pr99106.C
new file mode 100644 (file)
index 0000000..ccb48a9
--- /dev/null
+++ b/gcc/testsuite/g++.dg/ubsan/pr99106.C
@@ -0,0 +1,5 @@
+// PR sanitizer/99106
+// { dg-do compile }
+// { dg-options "-fsanitize=undefined" }
+
+#include "../ext/flexary38.C"