Re: [PATCH] [PR c++/84943] allow folding of array indexing indirect_ref

[Jason Merrill <jason at redhat dot com>]

On Tue, Apr 3, 2018 at 11:47 AM, Jason Merrill <jason@redhat.com> wrote:
> On Tue, Apr 3, 2018 at 3:44 AM, Alexandre Oliva <aoliva@redhat.com> wrote:
>> On Apr  2, 2018, Jason Merrill <jason@redhat.com> wrote:
>>
>>> On Sat, Mar 31, 2018 at 2:24 AM, Alexandre Oliva <aoliva@redhat.com> wrote:
>>>> On Mar 30, 2018, Jason Merrill <jason@redhat.com> wrote:
>>>>
>>>>> I don't think we need this; if arg is overloaded, we take the
>>>>> type_unknown_p early exit, so the code lower down is always dealing
>>>>> with a single function.
>>>>
>>>> Aah, that's why it seemed to me that we had already resolved overloads
>>>> when we got there.
>>>>
>>>> As a bonus, I added the tf_conv test before another mark_used call I'd
>>>> missed in the previous patch.
>>
>>> What if we check tf_conv in mark_used itself rather than at all the call sites?
>>
>> There are other uses of mark_used, but presumably we want them all to
>> be more conservative under tf_conv, so...  Here's what I'm testing.  Ok
>> if it passes?
>>
>>
>> [PR c++/84943] mark function as used when taking its address
>>
>> fn[0]() ICEd because we would fold the INDIRECT_REF used for the
>> array indexing while building the address for the call, after not
>> finding the decl hiding there at first.  But the decl would be exposed
>> by the folding, and then lower layers would complain we had the decl,
>> after all, but it wasn't one of the artificial or special functions
>> that could be called without being marked as used.
>>
>> This patch arranges for a FUNCTION_DECL to be marked as used when
>> taking its address, just like we already did when taking the address
>> of a static function to call it as a member function (i.e. using the
>> obj.fn() notation).  However, we shouldn't mark functions as used when
>> just performing overload resolution, lest we might instantiate
>> templates we shouldn't, as in g++.dg/overload/template1.C, so we
>> adjust mark_used to return early when testing conversions.
>>
>>
>> for  gcc/cp/ChangeLog
>>
>>         PR c++/84943
>>         * typeck.c (cp_build_addr_expr_1): Mark FUNCTION_DECL as
>>         used.
>>         * decl2.c (mark_used): Return without effects if tf_conv.
>>
>> for  gcc/testsuite/ChangeLog
>>
>>         PR c++/84943
>>         * g++.dg/pr84943.C: New.
>>         * g++.dg/pr84943-2.C: New.
>> ---
>>  gcc/cp/decl2.c                   |    6 ++++
>>  gcc/cp/typeck.c                  |    3 ++
>>  gcc/testsuite/g++.dg/pr84943-2.C |   64 ++++++++++++++++++++++++++++++++++++++
>>  gcc/testsuite/g++.dg/pr84943.C   |    8 +++++
>>  4 files changed, 81 insertions(+)
>>  create mode 100644 gcc/testsuite/g++.dg/pr84943-2.C
>>  create mode 100644 gcc/testsuite/g++.dg/pr84943.C
>>
>> diff --git a/gcc/cp/decl2.c b/gcc/cp/decl2.c
>> index fa753749e1a6..740e85b35617 100644
>> --- a/gcc/cp/decl2.c
>> +++ b/gcc/cp/decl2.c
>> @@ -5201,6 +5201,12 @@ maybe_instantiate_decl (tree decl)
>>  bool
>>  mark_used (tree decl, tsubst_flags_t complain)
>>  {
>> +  /* If we're just testing conversions or resolving overloads, we
>> +     don't want any permanent effects like forcing functions to be
>> +     output or instantiating templates.  */
>> +  if ((complain & tf_conv))
>> +    return false;
>
> I think we want to return true.

(OK with that change.)

Jason