Slim lto objects

[Jan Hubicka]

Hi,
this patch implements slim LTO. It is updated version of Andi's patch.  It is
done by terminating IPA optimization after analyzing and outputting LTO and in
compile_file skipping stuff that outputs assembly.

After some consideration I neded up with -ffat-lto-objects and
-fno-fat-lto-objects.  Original andi's patch used simply -flto-slim that is now
equivalent of -flto -fno-fat-lto-objects.

The reason is that having switch to enable/disable fat objects is that it
allows to flip the default to slim LTO in the future, unlike -flto-slim does.
I hope that after some time the default build environments will be sane enough
to work with slim lto. I.e.

1) compilation go through GCC driver and w/o calling linker directly.
   This is needed to make LTO work at all.
2) we will eventually drop collect2 path that doesn't work with slim LTO
   in favour of linker plugins everywhere. This need someone to implement
   glue to darwin linker plugin API
3) ar/nm and friends updated to deal with GCC linker plugin by default.
   BFD already has search path for plugins, we need to install our plugin there
   and deal sanely with multiple versions of LTO.

Incrementally I would like to do
1) Make testsuite to cover both slim and fat lto.  I tested the patch with
   -fno-fat-lto-objects. Some testsuite updating is needed because
   a) we output some diagnostics still from expand and those don't come out
      for compile only tests with -fno-fat-lto-objects. We probably could move
      all this safely to end of early opts.
   b) we will need to detect linker plugin default and don't test
      -fno-fat-lto-objects
2) Andi has wrappers for ar/nm to enable plugin
3) For bootstrap with slim LTO we also need libtool update.

Honza

	Andi Kleen  <ak@linux.intel.com>
	Jan Hubicka  <jh@suse.cz>
	* doc/invoke.texi (ffat-lto-objects): Document.
	* toplev.c (compile_file): Do not output assembly when doing slim lto;
	Output __gnu_slim_lto when doing slim lto.
	* cgraphunit.c (ipa_passes): Do only analysis when producing slim lto.
	(cgraph_optimize): Return early when doing slim lto.
	* opts.c (finish_options): Complain about lack of linker plugin
	when doing slim lto.
	* common.opt (ffat-lto-objects): New.
Index: doc/invoke.texi
===================================================================
*** doc/invoke.texi	(revision 179188)
--- doc/invoke.texi	(working copy)
*************** Objective-C and Objective-C++ Dialects}.
*** 355,362 ****
  -fcx-limited-range @gol
  -fdata-sections -fdce -fdce -fdelayed-branch @gol
  -fdelete-null-pointer-checks -fdse -fdevirtualize -fdse @gol
! -fearly-inlining -fipa-sra -fexpensive-optimizations -ffast-math @gol
! -ffinite-math-only -ffloat-store -fexcess-precision=@var{style} @gol
  -fforward-propagate -ffp-contract=@var{style} -ffunction-sections @gol
  -fgcse -fgcse-after-reload -fgcse-las -fgcse-lm -fgraphite-identity @gol
  -fgcse-sm -fif-conversion -fif-conversion2 -findirect-inlining @gol
--- 355,362 ----
  -fcx-limited-range @gol
  -fdata-sections -fdce -fdce -fdelayed-branch @gol
  -fdelete-null-pointer-checks -fdse -fdevirtualize -fdse @gol
! -fearly-inlining -fipa-sra -fexpensive-optimizations -ffat-lto-objects @gol
! -ffast-math -ffinite-math-only -ffloat-store -fexcess-precision=@var{style} @gol
  -fforward-propagate -ffp-contract=@var{style} -ffunction-sections @gol
  -fgcse -fgcse-after-reload -fgcse-las -fgcse-lm -fgraphite-identity @gol
  -fgcse-sm -fif-conversion -fif-conversion2 -findirect-inlining @gol
*************** use it.
*** 7891,7896 ****
--- 7891,7912 ----
  Enabled by default when LTO support in GCC is enabled and GCC was compiled
  with a linker supporting plugins (GNU ld 2.21 or newer or gold).
  
+ @item -ffat-lto-objects
+ @opindex ffat-lto-objects
+ Fat LTO objects are object files that contain both the intermediate language
+ and the object code. This makes them useable for both LTO linking and normal
+ linking. This option makes effect only with @option{-flto} and is ignored 
+ at linktime.
+ 
+ @option{-fno-fat-lto-objects} improves compilation time over plain LTO, but
+ requires the complete toolchain to be aware of LTO. Requires a linker with
+ linker plugin support for basic functionality.  Nm, ar and ranlib has to be
+ also linker plugin enabled to allow full featured build environment (capable of
+ building static libraries etc).
+ 
+ The default is @option{-ffat-lto-objects} but this default is intended to
+ change in future releases when linker plugin enabled environments become more
+ common.
  @item -fcompare-elim
  @opindex fcompare-elim
  After register allocation and post-register allocation instruction splitting,
Index: toplev.c
===================================================================
*** toplev.c	(revision 179188)
--- toplev.c	(working copy)
*************** compile_file (void)
*** 569,608 ****
        return;
      }
  
!   varpool_assemble_pending_decls ();
!   finish_aliases_2 ();
  
!   /* Likewise for mudflap static object registrations.  */
!   if (flag_mudflap)
!     mudflap_finish_file ();
  
!   output_shared_constant_pool ();
!   output_object_blocks ();
  
!   /* Write out any pending weak symbol declarations.  */
!   weak_finish ();
  
!   /* This must be at the end before unwind and debug info.
!      Some target ports emit PIC setup thunks here.  */
!   targetm.asm_out.code_end ();
  
!   /* Do dbx symbols.  */
!   timevar_push (TV_SYMOUT);
  
! #if defined DWARF2_DEBUGGING_INFO || defined DWARF2_UNWIND_INFO
!   if (dwarf2out_do_frame ())
!     dwarf2out_frame_finish ();
! #endif
  
!   (*debug_hooks->finish) (main_input_filename);
!   timevar_pop (TV_SYMOUT);
  
!   /* Output some stuff at end of file if nec.  */
  
!   dw2_output_indirect_constants ();
  
!   /* Flush any pending external directives.  */
!   process_pending_assemble_externals ();
  
    /* Emit LTO marker if LTO info has been previously emitted.  This is
       used by collect2 to determine whether an object file contains IL.
--- 569,613 ----
        return;
      }
  
!   /* Compilation unit is finalized.  When producing non-fat LTO object, we are
!      basically finished.  */
!   if (in_lto_p || !flag_lto || flag_fat_lto_objects)
!     {
!       varpool_assemble_pending_decls ();
!       finish_aliases_2 ();
  
!       /* Likewise for mudflap static object registrations.  */
!       if (flag_mudflap)
! 	mudflap_finish_file ();
  
!       output_shared_constant_pool ();
!       output_object_blocks ();
  
!       /* Write out any pending weak symbol declarations.  */
!       weak_finish ();
  
!       /* This must be at the end before unwind and debug info.
! 	 Some target ports emit PIC setup thunks here.  */
!       targetm.asm_out.code_end ();
  
!       /* Do dbx symbols.  */
!       timevar_push (TV_SYMOUT);
  
!     #if defined DWARF2_DEBUGGING_INFO || defined DWARF2_UNWIND_INFO
!       if (dwarf2out_do_frame ())
! 	dwarf2out_frame_finish ();
!     #endif
  
!       (*debug_hooks->finish) (main_input_filename);
!       timevar_pop (TV_SYMOUT);
  
!       /* Output some stuff at end of file if nec.  */
  
!       dw2_output_indirect_constants ();
  
!       /* Flush any pending external directives.  */
!       process_pending_assemble_externals ();
!    }
  
    /* Emit LTO marker if LTO info has been previously emitted.  This is
       used by collect2 to determine whether an object file contains IL.
*************** compile_file (void)
*** 623,628 ****
--- 628,650 ----
  			 (unsigned HOST_WIDE_INT) 1,
  			 (unsigned HOST_WIDE_INT) 1);
  #endif
+       /* Let linker plugin know that this is a slim object and must be LTOed
+          even when user did not ask for it.  */
+       if (!flag_fat_lto_objects)
+         {
+ #if defined ASM_OUTPUT_ALIGNED_DECL_COMMON
+ 	  ASM_OUTPUT_ALIGNED_DECL_COMMON (asm_out_file, NULL_TREE,
+ 					  "__gnu_slim_lto",
+ 					  (unsigned HOST_WIDE_INT) 1, 8);
+ #elif defined ASM_OUTPUT_ALIGNED_COMMON
+ 	  ASM_OUTPUT_ALIGNED_COMMON (asm_out_file, "__gnu_slim_lto",
+ 				     (unsigned HOST_WIDE_INT) 1, 8);
+ #else
+ 	  ASM_OUTPUT_COMMON (asm_out_file, "__gnu_slim_lto",
+ 			     (unsigned HOST_WIDE_INT) 1,
+ 			     (unsigned HOST_WIDE_INT) 1);
+ #endif
+         }
      }
  
    /* Attach a special .ident directive to the end of the file to identify
Index: cgraphunit.c
===================================================================
*** cgraphunit.c	(revision 179188)
--- cgraphunit.c	(working copy)
*************** ipa_passes (void)
*** 2042,2048 ****
    if (flag_generate_lto)
      targetm.asm_out.lto_end ();
  
!   if (!flag_ltrans)
      execute_ipa_pass_list (all_regular_ipa_passes);
    invoke_plugin_callbacks (PLUGIN_ALL_IPA_PASSES_END, NULL);
  
--- 2042,2048 ----
    if (flag_generate_lto)
      targetm.asm_out.lto_end ();
  
!   if (!flag_ltrans && (in_lto_p || !flag_lto || flag_fat_lto_objects))
      execute_ipa_pass_list (all_regular_ipa_passes);
    invoke_plugin_callbacks (PLUGIN_ALL_IPA_PASSES_END, NULL);
  
*************** cgraph_optimize (void)
*** 2080,2087 ****
    if (!seen_error ())
      ipa_passes ();
  
!   /* Do nothing else if any IPA pass found errors.  */
!   if (seen_error ())
      {
        timevar_pop (TV_CGRAPHOPT);
        return;
--- 2080,2088 ----
    if (!seen_error ())
      ipa_passes ();
  
!   /* Do nothing else if any IPA pass found errors or if we are just streaming LTO.  */
!   if (seen_error ()
!       || (!in_lto_p && flag_lto && !flag_fat_lto_objects))
      {
        timevar_pop (TV_CGRAPHOPT);
        return;
Index: opts.c
===================================================================
*** opts.c	(revision 179188)
--- opts.c	(working copy)
*************** finish_options (struct gcc_options *opts
*** 779,785 ****
  #else
        error_at (loc, "LTO support has not been enabled in this configuration");
  #endif
!     }
    if ((opts->x_flag_lto_partition_balanced != 0) + (opts->x_flag_lto_partition_1to1 != 0)
         + (opts->x_flag_lto_partition_none != 0) >= 1)
      {
--- 779,787 ----
  #else
        error_at (loc, "LTO support has not been enabled in this configuration");
  #endif
!       if (!opts->x_flag_fat_lto_objects && !HAVE_LTO_PLUGIN)
!         error_at (loc, "-fno-fat-lto-objects are suppored only with linker plugin.");
! }
    if ((opts->x_flag_lto_partition_balanced != 0) + (opts->x_flag_lto_partition_1to1 != 0)
         + (opts->x_flag_lto_partition_none != 0) >= 1)
      {
Index: common.opt
===================================================================
*** common.opt	(revision 179188)
--- common.opt	(working copy)
*************** Enum(excess_precision) String(standard) 
*** 1087,1092 ****
--- 1087,1096 ----
  ffast-math
  Common
  
+ ffat-lto-objects
+ Common Var(flag_fat_lto_objects) Init(1)
+ Output lto objects containing both the intermediate language and binary output.
+ 
  ffinite-math-only
  Common Report Var(flag_finite_math_only) Optimization SetByCombined
  Assume no NaNs or infinities are generated