[PATCH] Integration of parallel standard algorithms for c++17

[Jonathan Wakely]

On 20/03/19 14:05 -0700, Thomas Rodgers wrote:

>
>Fixed a failing test.

Thanks. Apart from the changelog issue I mentioned on IRC, the only
other required change I see is in include/Makefile.am:

@@ -1480,7 +1512,9 @@ install-headers:
 	$(mkinstalldirs) $(DESTDIR)${host_installdir}/../ext
 	for file in ${ext_host_headers}; do \
 	  $(INSTALL_DATA) $${file} $(DESTDIR)${host_installdir}/../ext; done
-
+	$(mkinstalldirs) ($DESTDIR)${gxx_include_dir}/${pstl_builddir}

This needs to be $(DESTDIR) not ($DESTDIR).

***

I also see a couple of things that we probably can't fix for now, but
I'll mention them anyway for later consideration.

In <bits/glue_execution_defs.h> there's a local include using ""
instead of <> (see PR libstdc++/88066 for a similar case I changed
recently):

#include "execution_defs.h"

We could fix that one, but then *all* the relative includes in
include/pstl/*  use "" too. Do you think upstream would change to use
#include <pstl/blah.h> instead of #include "blah.h" ? It looks like
upstream uses <pstl/include/...> instead so maybe that's something to
change in your script to import the upstream code.

Even if we fix it, TBB headers use "" instead of <>.  And it might not
be a problem for any compiler except GCC, because only we support the
silly -I- option that makes this matter.


I also noticed that simply including <execution> (even if you don't
use anything from it) will cause a link-time dependency on TBB:

/usr/bin/ld: /tmp/ccd7w5Oo.o: in function `tbb::interface7::task_arena::current_thread_index()':
/usr/include/tbb/task_arena.h:358: undefined reference to `tbb::interface7::internal::task_arena_base::internal_current_slot()'
collect2: error: ld returned 1 exit status

This dependency comes from <tbb/partioner.h> which is included by
<tbb/parallel_scan.h> which is included by <bits/execution_defs.h>.

I think that's OK for now, as no existing code using GCC includes the
<execution> header (because it doesn't exist yet). It would be good if
we can find a way to solve that eventually though. Maybe the eventual
solution will just be a non-TBB backend using OpenMP.

Exporting something like this from libstdc++.so would work, but is
disgusting (and presumably "tbb::interface7" changes from release to
release?"):

extern "C" [[__gnu__::__weak__]]
int
_ZN3tbb10interface78internal15task_arena_base21internal_current_slotEv()
{ return -1; }