Re: [C++ Patch] PR 59571

[Jason Merrill <jason at redhat dot com>]

On 03/17/2014 05:38 AM, Paolo Carlini wrote:
> noticed this issue, which looks simple to fix. The ICE happens in
> cxx_eval_constant_expression, because it cannot handle a CAST_EXPR (or
> any othe *_CAST, for that matter). In fact check_narrowing calls
> maybe_constant_value, and, because we are in a template, the latter
> faces the unfolded CAST_EXPR. Thus it seems easy to just use
> fold_non_dependent_expr_sfinae. Tested x86_64-linux.

OK.

> PS: looking forward, I'm wondering if some semantics/typeck functions
> shouldn't try harder before building a tree node and returning, eg,
> instead of just checking processing_template_decl, actually checking if
> type and expr are dependent? Does this kind of audit make sense for next
> Stage 1?

In general adding fold_non_dependent_expr where it's needed is the right 
answer, because normal operation creates tree patterns that tsubst 
doesn't understand how to deal with.

I suppose it might work to always fully build 
non-instantiation-dependent expressions, wrap them in 
NON_DEPENDENT_EXPR, and then unshare its operand at instantiation time. 
 But that would be a significant change with unclear benefit.

Jason