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d1c6023698
This patch fixes a very annoying problem where we emit a bogus
check_out_of_consteval_use error. The error is provoked while
processing
[: std::meta::reflect_constant_array (data) :]
The argument of a [: :] is a constant-expression = a manifestly
constant-evaluated context, so any consteval-only exprs in it
are OK. But in eval_reflect_constant_array we do get_template_parm_object
which does push_to_top_level -- so we have no scope_chain, therefore
any in_consteval_if_p and current_function_decl are cleared, so we're
not in an immediate context. As part of this get_template_parm_object,
we call cp_finish_decl -> check_initializer -> build_aggr_init ->
-> build_vec_init.
Here in build_vec_init try_const is true, but we still generate code
for the initializer like
<<< Unknown tree: expr_stmt
(void) ++D.67757 >>>;
<<< Unknown tree: expr_stmt
(void) --D.67758 >>>;
etc. We add ++D.67757 with finish_expr_stmt which calls
convert_to_void -> check_out_of_consteval_use which causes the error
because ++D.67757's type is consteval-only. Note that what we end up using
is the simple
_ZTAX... = {{.name=<<< Unknown tree: reflect_expr _ZTAXtlA2_KcLS_95EEE >>>, .none=1}}
because we didn't see anything non-const in the initializer.
Rather than convincing check_out_of_consteval_use that we are in an
immediate context, we should only call check_out_of_consteval_use on the
outermost statement, not sub-statements like the ++D.67757 above. This
is not a complete fix though, see the FIXME.
PR c++/123662
PR c++/123611
gcc/cp/ChangeLog:
* cvt.cc (convert_to_void): Only call check_out_of_consteval_use
when stmts_are_full_exprs_p.
gcc/testsuite/ChangeLog:
* g++.dg/reflect/reflect_constant_array5.C: New test.
* g++.dg/reflect/reflect_constant_array6.C: New test.
Reviewed-by: Jason Merrill <jason@redhat.com>
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