21fd62e5ca
Here during constexpr evaluation of
std::construct_at(&a._M_value)
we find ourselves in cxx_eval_store_expression where the target object
is 'a._M_value' and the initializer is {}. Since _M_value is an empty
[[no_unique_address]] member we don't create a sub-CONSTRUCTOR for it,
so we end up in the early exit code path for empty stores with mismatched
types and trip over the assert therein
gcc_assert (is_empty_class (TREE_TYPE (init)) && !lval);
because lval is true. The reason it's true is because the INIT_EXPR in
question is the LHS of a COMPOUND_EXPR, and evaluation of the LHS is
always performed with lval=true (to indicate there's no lvalue-to-rvalue
conversion).
This patch makes the code path in question handle the lval=true case
appropriately rather than asserting. In passing, it also consolidates
the duplicate implementations of std::construct_at/destroy_at in some
of the C++20 constexpr tests into a common header file.
PR c++/101663
gcc/cp/ChangeLog:
* constexpr.c (cxx_eval_store_expression): Handle the lval=true
case in the early exit code path for empty stores with mismatched
types.
gcc/testsuite/ChangeLog:
* g++.dg/cpp2a/construct_at.h: New convenience header file that
defines minimal implementations of std::construct_at/destroy_at,
split out from ...
* g++.dg/cpp2a/constexpr-new5.C: ... here.
* g++.dg/cpp2a/constexpr-new6.C: Use the header.
* g++.dg/cpp2a/constexpr-new14.C: Likewise.
* g++.dg/cpp2a/constexpr-new20.C: New test.
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