Re: Questions about LTO infrastructure and pragma omp target

[Jakub Jelinek <jakub@redhat.com>]

On Fri, Aug 23, 2013 at 02:55:27PM +0400, Ilya Verbin wrote:
> I'm trying to implement the approach with modified lto-wrapper.
> Suppose we have a bytecode of the routine foo, streamed during ompexp pass into some section, say .gnu.omptarget_foo.
> In function lto.c:do_whole_program_analysis() an extra partition should be created, that will contain bytecode from .gnu.omptarget_foo, right?
> As far as I understood, in addition to the bytecode of foo, we should also stream extra symtab_nodes, and read them somewhere in lto-cgraph.c:input_symtab().
> This means we should maintain 2 symtabs inside WPA stage - original for host and new for target?

I don't think we should stream into more than one target section.
There should be just .gnu.target_lto section (or whatever other suitable
name) and should stream into it:
1) all functions and variables with "omp declare target" attribute
2) the outlined bodies of #pragma omp target turned into *.ompfn functions
3) all the types, symtab etc. needed for that

If compiling with -flto, you'll also get everything from the CU streamed
into the normal LTO section, otherwise you'll get assembly for the host
variables/functions/etc.

Then the question is what the plugin should perform with these sections,
whether it will compile each input .gnu.target_lto section hunk separately
(as in non-LTO mode), or with -flto also LTO them together.

	Jakub