[pushed] c++: constinit and value-initialization [PR119652]

[Jason Merrill]

Tested x86_64-pc-linux-gnu, applying to trunk and 14.

-- 8< --

Value-initialization built an AGGR_INIT_EXPR to set AGGR_INIT_ZERO_FIRST on.
Passing that AGGR_INIT_EXPR to maybe_constant_value returned a TARGET_EXPR,
which potential_constant_expression_1 mistook for a temporary.

We shouldn't add a TARGET_EXPR to the AGGR_INIT_EXPR in this case, just like
we already avoid adding it to CONSTRUCTOR or CALL_EXPR.

        PR c++/119652

gcc/cp/ChangeLog:

        * constexpr.cc (cxx_eval_outermost_constant_expr): Also don't add a
        TARGET_EXPR around AGGR_INIT_EXPR.

gcc/testsuite/ChangeLog:

        * g++.dg/cpp2a/constinit20.C: New test.
---
 gcc/cp/constexpr.cc                      |  3 ++-
 gcc/testsuite/g++.dg/cpp2a/constinit20.C | 18 ++++++++++++++++++
 2 files changed, 20 insertions(+), 1 deletion(-)
 create mode 100644 gcc/testsuite/g++.dg/cpp2a/constinit20.C

diff --git a/gcc/cp/constexpr.cc b/gcc/cp/constexpr.cc
index 37ea65cb655..497f64f3cea 100644
--- a/gcc/cp/constexpr.cc
+++ b/gcc/cp/constexpr.cc
@@ -9316,7 +9316,8 @@ cxx_eval_outermost_constant_expr (tree t, bool 
allow_non_constant,
       if (TREE_CODE (t) == TARGET_EXPR
          && TARGET_EXPR_INITIAL (t) == r)
        return t;
-      else if (TREE_CODE (t) == CONSTRUCTOR || TREE_CODE (t) == CALL_EXPR)
+      else if (TREE_CODE (t) == CONSTRUCTOR || TREE_CODE (t) == CALL_EXPR
+              || TREE_CODE (t) == AGGR_INIT_EXPR)
        /* Don't add a TARGET_EXPR if our argument didn't have one.  */;
       else if (TREE_CODE (t) == TARGET_EXPR && TARGET_EXPR_CLEANUP (t))
        r = get_target_expr (r);
diff --git a/gcc/testsuite/g++.dg/cpp2a/constinit20.C 
b/gcc/testsuite/g++.dg/cpp2a/constinit20.C
new file mode 100644
index 00000000000..9b043917dc3
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/constinit20.C
@@ -0,0 +1,18 @@
+// PR c++/119652
+// { dg-do compile { target c++20 } }
+
+struct __shared_count {
+  constexpr __shared_count() {}
+  ~__shared_count();
+  int _M_pi = 0;
+};
+struct shared_ptr {
+  __shared_count _M_refcount;
+};
+struct A {
+  A() = default;
+  shared_ptr m;
+};
+constinit A a;
+constinit A b {};
+constinit A c = {};

base-commit: 3a77a567b1028a28ecbb2f2eadc351d8bd004352
-- 
2.49.0