Re: [C++ Patch] PR 85112 ("[8 Regression] ICE with invalid constexpr")

[Paolo Carlini <paolo dot carlini at oracle dot com>]

Hi,

On 13/04/2018 16:06, Jason Merrill wrote:
> On Fri, Apr 13, 2018 at 5:05 AM, Paolo Carlini <paolo.carlini@oracle.com> wrote:
> > Hi,
> >
> > in this error-recovery regression, after a sensible error message issued by
> > cxx_constant_init, store_init_value stores an error_mark_node as
> > DECL_INITIAL of the VAR_DECL for 'j'. This error_mark_node reappears much
> > later, to cause a crash during gimplification. As far as I know, the choice
> > of storing error_mark_nodes too is the outcome of a rather delicate
> > error-recovery strategy and I don't think we want to revisit it at this
> > time, thus the remaining option is catching later the error_mark_node, at a
> > "good" time. I note, in passing, that the do loop in gimplify_expr which
> > uses the crashing STRIP_USELESS_TYPE_CONVERSION seems a bit lacking from the
> > error-recovery point of view, because at each iteration it *does* cover for
> > error_operand_p (save_expr) but only immediately after the call, when it's
> > too late.
> >
> > All the above said, I believe that at least for the 8.1.0 needs we may want
> > to catch the error_mark_node in cp_build_modify_expr, when we are handling
> > the assignment 'a.n = j;': convert_for_assignment produces a NOP_EXPR from
> > the VAR_DECL for 'j' which then cp_convert_and_check regenerates (deep in
> > convert_to_integer_1 via maybe_fold_build1_loc) in the final bare-bone form,
> > with the error_mark_node as the first operand. Passes testing on
> > x86_64-linux.
> We should avoid wrapping an error_mark_node in a NOP_EXPR in the first place.
Basing on my analysis, that's easy to do, in convert_to_integer_1. I 
wasn't sure we wanted to touch such basic facilities ;) 
Implementation-wise, I wondered whether we wanted to handle NOP_EXPR and 
error_mark_node specially inside build1 itself, but, again, that seems a 
bit invasive, plus all the build* facilities always allocate a new node 
as the first step. Anyway, fully testing the below will require a bit of 
time, shall I go ahead with that, given that g++.dg passed?

Thanks!
Paolo.

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