c++: fix ICE with constexpr ARRAY_REF [PR110382]
This code in cxx_eval_array_reference has been hard to get right.
In r12-2304 I added some code; in r13-5693 I removed some of it.
Here the problematic line is "S s = arr[0];" which causes a crash
on the assert in verify_ctor_sanity:
gcc_assert (!ctx->object || !DECL_P (ctx->object)
|| ctx->global->get_value (ctx->object) == ctx->ctor);
ctx->object is the VAR_DECL 's', which is correct here. The second
line points to the problem: we replaced ctx->ctor in
cxx_eval_array_reference:
new_ctx.ctor = build_constructor (elem_type, NULL); // #1
which I think we shouldn't have; the CONSTRUCTOR we created in
cxx_eval_constant_expression/DECL_EXPR
new_ctx.ctor = build_constructor (TREE_TYPE (r), NULL);
had the right type.
We still need #1 though. E.g., in constexpr-96241.C, we never
set ctx.ctor/object before calling cxx_eval_array_reference, so
we have to build a CONSTRUCTOR there. And in constexpr-101371-2.C
we have a ctx.ctor, but it has the wrong type, so we need a new one.
We can fix the problem by always clearing the object, and, as an
optimization, only create/free a new ctor when actually needed.
PR c++/110382
gcc/cp/ChangeLog:
* constexpr.cc (cxx_eval_array_reference): Create a new constructor
only when we don't already have a matching one. Clear the object
when the type is non-scalar.
gcc/testsuite/ChangeLog:
* g++.dg/cpp1y/constexpr-110382.C: New test.