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Re: [gomp4] Add tables generation

From: Thomas Schwinge <thomas at codesourcery dot com>
To: Ilya Verbin <iverbin at gmail dot com>, Bernd Schmidt <bernds at codesourcery dot com>
Cc: Jakub Jelinek <jakub at redhat dot com>, GCC Patches <gcc-patches at gcc dot gnu dot org>
Date: Thu, 4 Sep 2014 15:08:06 +0200
Subject: Re: [gomp4] Add tables generation
Authentication-results: sourceware.org; auth=none
References: <20140327161651 dot GC1817 at tucnak dot redhat dot com> <20140417183329 dot GA16810 at msticlxl57 dot ims dot intel dot com> <53970DA3 dot 20809 at codesourcery dot com> <20140610180658 dot GA27730 at msticlxl57 dot ims dot intel dot com> <20140813161914 dot GA26226 at msticlxl57 dot ims dot intel dot com> <20140818160759 dot GA60399 at msticlxl57 dot ims dot intel dot com> <53F228CD dot 70800 at codesourcery dot com> <20140819103921 dot GA62436 at msticlxl57 dot ims dot intel dot com> <53F33B16 dot 5000809 at codesourcery dot com> <20140819132706 dot GC62436 at msticlxl57 dot ims dot intel dot com> <20140902174946 dot GA52247 at msticlxl57 dot ims dot intel dot com>

Hi!

On Tue, 2 Sep 2014 21:49:46 +0400, Ilya Verbin <iverbin@gmail.com> wrote:
> This patch allows to compile binaries with offloading without passing -flto option, and
> w/o performing link-time optimizations of the host code.

Thanks for working on this!

> How it works:
> 1.  If there is at least one function or global variable to offload, gcc sets flag_generate_lto.
> This enables writing the bytecode produced by ipa_write_summaries into
> .gnu.target_lto_* sections (.gnu.lto_* sections are not created).
> Also this flag emits LTO marker (__gnu_lto_v1).
> 2.  This step is not changed: collect2 scans object files for the LTO marker and fills the list
> of LTO objects.  If the list is not empty, it runs lto-wrapper to perform link-time recompilation.
> 3.  lto-wrapper compiles images for targets.  And if -flto option is absent
> (lto_mode == LTO_MODE_NONE), then it just returns the list of input objects without recompilation.

That seems sane to me.  (But you guys have looked into this design/code
in much more detail than I have.)

I'm facing one problem; I guess the crucial detail is that in my scenario
I'm using the linker plugin.  The lto-wrapper is not being executed (and
thus no mkoffload being run), because Ânum_claimed_files == 0Â.  In
lto-plugin/lto-plugin.c:process_symtab, only LTO_SECTION_PREFIX
(".gnu.lto_.symtab") is considered, which (correctly so) is not generated
anymore by GCC in the new scenario, but ".gnu.target_lto_" is not
considered there.  (Should this maybe look only for the LTO marker
"__gnu_lto_v1", or am I misunderstanding what this is doing?)  If I make
that also accept the offloading section, the compilation process proceeds
further, but still fails, because no resolution file is available:
Â[...]/ld: cannot find -fresolution=/tmp/cc7xeiW0.res: No such file or
directoryÂ.  Is this enough information for someone who is more familiar
with the design/code to already see what needs to be done?

GrÃÃe,
 Thomas

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Follow-Ups:
- Re: [gomp4] Add tables generation
  - From: Ilya Verbin
- Re: [gomp4] Add tables generation
  - From: Thomas Schwinge

References:
- Re: [gomp4] Add tables generation
  - From: Ilya Verbin

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