[gcc r12-8024] c++: -Wunused-value and array init [PR104702]

[Jason Merrill]

https://gcc.gnu.org/g:cc76c502a761ddaee215bcbd8fe4720e46d3b9dd

commit r12-8024-gcc76c502a761ddaee215bcbd8fe4720e46d3b9dd
Author: Jason Merrill <jason@redhat.com>
Date:   Wed Apr 6 10:59:40 2022 -0400

    c++: -Wunused-value and array init [PR104702]
    
    Here, because of problems with the new warning-control code and expressions
    that change location, the suppress_warning on the INDIRECT_REF didn't work.
    Those problems still need to be worked out, but it's simple to avoid needing
    to use suppress_warning in the first place by using a reference instead.
    
            PR c++/104702
    
    gcc/cp/ChangeLog:
    
            * init.cc (build_vec_init): Use a reference for the result.
    
    gcc/testsuite/ChangeLog:
    
            * g++.dg/warn/Wunused-19.C: New test.

Diff:
---
 gcc/cp/init.cc                         |  5 ++---
 gcc/testsuite/g++.dg/warn/Wunused-19.C | 16 ++++++++++++++++
 2 files changed, 18 insertions(+), 3 deletions(-)

diff --git a/gcc/cp/init.cc b/gcc/cp/init.cc
index 01e762320f3..c20ed211f1d 100644
--- a/gcc/cp/init.cc
+++ b/gcc/cp/init.cc
@@ -4908,10 +4908,9 @@ build_vec_init (tree base, tree maxindex, tree init,
   /* Now make the result have the correct type.  */
   if (TREE_CODE (atype) == ARRAY_TYPE)
     {
-      atype = build_pointer_type (atype);
+      atype = build_reference_type (atype);
       stmt_expr = build1 (NOP_EXPR, atype, stmt_expr);
-      stmt_expr = cp_build_fold_indirect_ref (stmt_expr);
-      suppress_warning (stmt_expr /* What warning? */);
+      stmt_expr = convert_from_reference (stmt_expr);
     }
 
   return stmt_expr;
diff --git a/gcc/testsuite/g++.dg/warn/Wunused-19.C b/gcc/testsuite/g++.dg/warn/Wunused-19.C
new file mode 100644
index 00000000000..2fc70b04c18
--- /dev/null
+++ b/gcc/testsuite/g++.dg/warn/Wunused-19.C
@@ -0,0 +1,16 @@
+// PR c++/104702
+// { dg-additional-options "-fno-exceptions -Wunused-value" }
+
+struct FlyString {
+  FlyString(char const*);
+  ~FlyString();
+};
+
+struct Array { FlyString __data[1]; };
+
+void frobnicate(Array&);
+
+int main() {
+    Array s_reserved_words = { "" }; // { dg-bogus "value computed is not used" }
+    frobnicate(s_reserved_words);
+}