Re: [PATCH] Destroy arguments for _Cilk_spawn calling in the child (PR 80038)

[Richard Biener <richard.guenther@gmail.com>]

On Wed, Apr 12, 2017 at 11:16 PM, Jeff Law <law@redhat.com> wrote:
> On 04/07/2017 08:02 AM, Xi Ruoyao wrote:
>>
>> On 2017-04-06 11:12 -0600, Jeff Law wrote:
>>
>>> With the likely deprecation in mind, I've only done a cursory review of
>>> the changes -- mostly to verify that they hit Cilk+ paths only.
>>
>>
>>> What's the purpose behind changing when we set the in_lto_p flag?
>>
>>
>> Without that change, GCC with my patch ICEed with _Cilk_spawn and
>> -flto -O3 -fcilkplus since __cilkrts_stack_frame.ctx's type (array of void
>> *)
>> was not TYPE_STRUCTURAL_EQUALITY_P in lto stage.
>> If this change is not proper, I'll work on modifying my patch to work
>> without touching in_lto_p.
>
> It's certainly be preferable to not change in_lto_p-- unless Richi wants to
> chime in on the safety of setting in_lto_p earlier.
>
> I'm not familiar enough with the LTO interactions to know if movement of
> in_lto_p is safe.

It should be safe and even technically more correct given we now have
various conditionals in the type building routines in tree.c that check
in_lto_p and avoid setting TYPE_CANONICAL from them -- TYPE_CANONICAL
is re-computed later, and for the builtin types we first zero TYPE_CANONICAL
(see lto.c:read_cgraph_and_symbols).

Now... I think those checks are somewhat wrong given that the middle-end
_does_ create types later, hopefully not ones we use for alias purposes,
but I'm not 100% sure.  So it somewhat feels like a hack ;)

So in theory the change is a good one.  I'm still nervous at this stage.

Did you verify LTO bootstrap still works with the patch?

CCing Honza who fiddled with this last (and introduced all those
in_lto_p checks).

Thanks,
Richard.

> Jeff