c++/c-common: Fix convert_vector_to_array_for_subscript for qualified vector types [PR89224]

After r7-987-gf17a223de829cb, the access for the elements of a vector type would lose the qualifiers.
So if we had `constvector[0]`, the type of the element of the array would not have const on it.
This was due to a missing build_qualified_type for the inner type of the vector when building the array type.
We need to add back the call to build_qualified_type and now the access has the correct qualifiers. So the
overloads and even if it is a lvalue or rvalue is correctly done.

Note we correctly now reject the testcase gcc.dg/pr83415.c which was incorrectly accepted after r7-987-gf17a223de829cb.

Built and tested for aarch64-linux-gnu.

	PR c++/89224

gcc/c-family/ChangeLog:

	* c-common.cc (convert_vector_to_array_for_subscript): Call build_qualified_type
	for the inner type.

gcc/cp/ChangeLog:

	* constexpr.cc (cxx_eval_array_reference): Compare main variants
	for the vector/array types instead of the types directly.

gcc/testsuite/ChangeLog:

	* g++.dg/torture/vector-subaccess-1.C: New test.
	* gcc.dg/pr83415.c: Change warning to error.

Signed-off-by: Andrew Pinski <quic_apinski@quicinc.com>

4 files changed, 32 insertions, 3 deletions

diff --git a/gcc/c-family/c-common.cc b/gcc/c-family/c-common.cc
index 032dcb4..aae998d 100644
--- a/gcc/c-family/c-common.cc
+++ b/gcc/c-family/c-common.cc
@@ -8964,6 +8964,7 @@ convert_vector_to_array_for_subscript (location_t loc,
   if (gnu_vector_type_p (TREE_TYPE (*vecp)))
     {
       tree type = TREE_TYPE (*vecp);
+      tree newitype;
 
       ret = !lvalue_p (*vecp);
 
@@ -8978,8 +8979,12 @@ convert_vector_to_array_for_subscript (location_t loc,
 	 for function parameters.  */
       c_common_mark_addressable_vec (*vecp);
 
+      /* Make sure qualifiers are copied from the vector type to the new element
+	 of the array type.  */
+      newitype = build_qualified_type (TREE_TYPE (type), TYPE_QUALS (type));
+
       *vecp = build1 (VIEW_CONVERT_EXPR,
-		      build_array_type_nelts (TREE_TYPE (type),
+		      build_array_type_nelts (newitype,
 					      TYPE_VECTOR_SUBPARTS (type)),
 		      *vecp);
     }
diff --git a/gcc/cp/constexpr.cc b/gcc/cp/constexpr.cc
index 50f799d..bd72533 100644
--- a/gcc/cp/constexpr.cc
+++ b/gcc/cp/constexpr.cc
@@ -4424,7 +4424,8 @@ cxx_eval_array_reference (const constexpr_ctx *ctx, tree t,
   if (!lval
       && TREE_CODE (ary) == VIEW_CONVERT_EXPR
       && VECTOR_TYPE_P (TREE_TYPE (TREE_OPERAND (ary, 0)))
-      && TREE_TYPE (t) == TREE_TYPE (TREE_TYPE (TREE_OPERAND (ary, 0))))
+      && (TYPE_MAIN_VARIANT (TREE_TYPE (t))
+	  == TYPE_MAIN_VARIANT (TREE_TYPE (TREE_TYPE (TREE_OPERAND (ary, 0))))))
     ary = TREE_OPERAND (ary, 0);
 
   tree oldidx = TREE_OPERAND (t, 1);
diff --git a/gcc/testsuite/g++.dg/torture/vector-subaccess-1.C b/gcc/testsuite/g++.dg/torture/vector-subaccess-1.C
new file mode 100644
index 0000000..0c8958a
--- /dev/null
+++ b/gcc/testsuite/g++.dg/torture/vector-subaccess-1.C
@@ -0,0 +1,23 @@
+/* PR c++/89224 */
+
+/* The access of `vector[i]` has the same qualifiers as the original
+   vector which was missing. */
+
+typedef __attribute__((vector_size(16))) unsigned char  Int8x8_t;
+
+template <class T>
+void g(T &x) {
+    __builtin_abort();
+}
+template <class T>
+void g(const T &x) {
+  __builtin_exit(0);
+}
+void f(const Int8x8_t x) {
+  g(x[0]);
+}
+int main(void)
+{
+    Int8x8_t x ={};
+    f(x);
+}
diff --git a/gcc/testsuite/gcc.dg/pr83415.c b/gcc/testsuite/gcc.dg/pr83415.c
index 5934c16..2fc8503 100644
--- a/gcc/testsuite/gcc.dg/pr83415.c
+++ b/gcc/testsuite/gcc.dg/pr83415.c
@@ -7,6 +7,6 @@ int
 main (int argc, short *argv[])
 {
   int i = argc;
-  y[i] = 7 - i; /* { dg-warning "read-only" } */
+  y[i] = 7 - i; /* { dg-error "read-only" } */
   return 0;
 }