c++: wrong error with constexpr array and value-init [PR108158]
In this test case, we find ourselves evaluating 't' which is
((const struct carray *) this)->data_[VIEW_CONVERT_EXPR<long int>(index)]
in cxx_eval_array_reference. ctx->object is non-null, a RESULT_DECL, so
we replace it with 't':
new_ctx.object = t; // result_decl replaced
and then we go to cxx_eval_constant_expression to evaluate an
AGGR_INIT_EXPR, where we end up evaluating an INIT_EXPR (which is in the
body of the constructor for seed_or_index):
((struct seed_or_index *) this)->value_ = NON_LVALUE_EXPR <0>
whereupon in cxx_eval_store_expression we go to the probe loop
where the 'this' is evaluated to
ze_set.tables_.first_table_.data_[0]
so the 'object' is ze_set, but that isn't in ctx->global->get_value_ptr
so we fail with a bogus error. ze_set is not there because it comes
from a different constexpr context (it's not in cv_cache either).
The problem started with r12-2304 where I added the new_ctx.object
replacement. That was to prevent a type mismatch: the type of 't'
and ctx.object were different.
It seems clear that we shouldn't have replaced ctx.object here.
The cxx_eval_array_reference I mentioned earlier is called from
cxx_eval_store_expression:
6257 init = cxx_eval_constant_expression (&new_ctx, init, vc_prvalue,
6258 non_constant_p, overflow_p);
which already created a new context, whose .object we should be
using unless, for instance, INIT contained a.b and we're evaluating
the 'a' part, which I think was the case for r12-2304; in that case
ctx.object has to be something different.
It no longer seems necessary to replace new_ctx.object (likely due to
changes in empty class handling).
PR c++/108158
gcc/cp/ChangeLog:
* constexpr.cc (cxx_eval_array_reference): Don't replace
new_ctx.object.
gcc/testsuite/ChangeLog:
* g++.dg/cpp1y/constexpr-108158.C: New test.