RE: [PATCH]middle-end: Recursively check is_trivially_copyable_or_pair in vec.h

[Tamar Christina <Tamar.Christina@arm.com>]

> -----Original Message-----
> From: Jakub Jelinek <jakub@redhat.com>
> Sent: Monday, October 2, 2023 2:21 PM
> To: Tamar Christina <Tamar.Christina@arm.com>
> Cc: gcc-patches@gcc.gnu.org; nd <nd@arm.com>; jwakely@redhat.com
> Subject: Re: [PATCH]middle-end: Recursively check
> is_trivially_copyable_or_pair in vec.h
> 
> On Mon, Oct 02, 2023 at 01:38:53PM +0100, Tamar Christina wrote:
> > Hi All,
> >
> > I recently committed a patch that uses a nested std::pair in the second
> argument.
> > It temporarily adds a second ranking variable for sorting and then later drops
> it.
> >
> > This hits the newly added assert in vec.h.  This assert made some
> > relaxation for std::pair but doesn't allow this case through.  The
> > patch allows a recursive std::pair in the second argument which fixes
> bootstrap.
> 
> I must say I still don't understand why using a struct ifcvt_arg_entry { tree arg;
> unsigned len, occur; }; with comments describing what the members mean
> wouldn't be a better fix, in the sorting function what exactly means
> x{1,2}.second.first and x{1,2}.second.second isn't easily understandable,
> neither from the identifiers nor from any comments.
> Seems because you use 2 separate vectors, one with just tree elements and
> another with those tree elements + 2 unsigned values cached from it for the
> sorting purpose and then rewrite the original tree vector after sorting, I don't
> really see why nested std::pair would be a better match for it than a named
> structure.  Furthermore, why populate args first, then compute the extra 2
> integers in another loop pushing to argsKV and finally overwrite args with
> sorted values?  Can't the first loop push tree with the 2 integers already?  And
> what is the point of not using this structure later on when both args and
> argsKV vectors are live until the end of the same function?
> Can't you either pass that argsKV to others, having just one vector, or at least
> release the other vector when you don't really need it?
> Formatting style, swap? arg1 : arg0 isn't correctly formatted, missing space
> before ?.
> 
> Also, ArgEntry is CamelCase which we (usually) don't use in GCC and
> additionally doesn't seem to be unique enough for ODR purposes.
> Ditto argsKV.

Ok, since these will take a lot longer to test and do I've reverted the patch
for now since bootstrap was broken.

Thanks,
Tamar

> 
> > It should also still maintain the invariant that was being tested here
> > since the nested arguments should still be trivially copyable.
> >
> > Bootstrapped on aarch64-none-linux-gnu, x86_64-linux-gnu, and no issues.
> >
> > Ok for master?
> >
> > Thanks,
> > Tamar
> >
> > gcc/ChangeLog:
> >
> > 	vec.h (struct is_trivially_copyable_or_pair): Check recursively in
> 
> Missing "* " above.
> 
> > 	second arg.
> 
> 	Jakub