PING^1 [PATCH] inline: Rebuild target option node for caller [PR105459]

Jan Hubicka hubicka@kam.mff.cuni.cz
Fri Jul 1 09:20:57 GMT 2022


> On Thu, Jun 23, 2022 at 4:03 AM Kewen.Lin <linkw@linux.ibm.com> wrote:
> >
> > Hi,
> >
> > Gentle ping https://gcc.gnu.org/pipermail/gcc-patches/2022-June/596212.html
> >
> > BR,
> > Kewen
> >
> > on 2022/6/6 14:20, Kewen.Lin via Gcc-patches wrote:
> > > Hi,
> > >
> > > PR105459 exposes one issue in inline_call handling that when it
> > > decides to copy FP flags from callee to caller and rebuild the
> > > optimization node for caller fndecl, it's possible that the target
> > > option node is also necessary to be rebuilt.  Without updating
> > > target option node early, it can make nodes share the same target
> > > option node wrongly, later when we want to unshare it somewhere
> > > (like in target hook) it can get unexpected results, like ICE on
> > > uninitialized secondary member of target globals exposed in this PR.
> 
> I think that
> 
>   /* Reload global optimization flags.  */
>   if (reload_optimization_node && DECL_STRUCT_FUNCTION (to->decl) == cfun)
>     set_cfun (cfun, true);
> 
> is supposed to do that via ix86_set_current_function which will eventually
> re-build the target optimization node exactly for this reason.
> 
> But with LTO we arrive here during WPA time only and there cfun is NULL
> (and so is DECL_STRUCT_FUNCTION (to->decl)), so the target doesn't
> get the chance to fix things up here.

I see this logic was added by Martin in 2017 and it indeed looks bit
odd, but I suppose it is intended primarily for early inliner where cfun
is non-NULL and we really need to update global state.
> 
> Now, it should be fine to delay this fixup until we set the cfun at LTRANS
> time but there we run into
> 
>   if (old_tree != new_tree)
>     {
>       cl_target_option_restore (&global_options, &global_options_set,
>                                 TREE_TARGET_OPTION (new_tree));
> ...
>     }
>   else if (flag_unsafe_math_optimizations
>            != TREE_TARGET_OPTION (new_tree)->x_ix86_unsafe_math_optimizations
>            || (flag_excess_precision
>                != TREE_TARGET_OPTION (new_tree)->x_ix86_excess_precision))
>     {
> ... FIXUP! ...
> 
> and old_tree != new_tree disables the fixup.
> 
> When we refactor the above to always consider the FP flag change (so apply it
> lazily), then this fixes the testcase in the PR as well.  Thus something like
> the attached.
> 
> Ideally this stuff would be refactored to a target hook that can work without
> the set_cfun, also working towards merging the target and optimization node
> since they have to be kept in sync ...
> 
> I think your proposed patch makes another variant through the maze to
> do something at WPA time but that makes it all even more complicated :/
> 
> Sorry for the delay btw.
> 
> Folks - any other opinions?

Your patch looks reasonable to me... Indeed working on nodes directly
would be nicer, but that means bigger surgery in the optimization
handling right?

Thanks,
Honza
> 
> Thanks,
> Richard.
> 
> > > Commit r12-3721 makes it get exact fp_expression info and causes
> > > more optimization chances then exposes this issue.  Commit r11-5855
> > > introduces two target options to shadow flag_excess_precision and
> > > flag_unsafe_math_optimizations and shows the need to rebuild target
> > > node in inline_call when optimization node changes.
> > >
> > > As commented in PR105459, I tried to postpone init_function_start
> > > in cgraph_node::expand, but abandoned it since I thought it just
> > > concealed the issue.  And I also tried to adjust the target node
> > > when current function switching, but failed since we get the NULL
> > > cfun and fndecl in WPA phase.
> > >
> > > Bootstrapped and regtested on x86_64-redhat-linux, powerpc64-linux-gnu
> > > P8 and powerpc64le-linux-gnu P9.
> > >
> > > Any thoughts?  Is it OK for trunk?
> > >
> > > BR,
> > > Kewen
> > > -----
> > >
> > >       PR tree-optimization/105459
> > >
> > > gcc/ChangeLog:
> > >
> > >       * ipa-inline-transform.cc (inline_call): Rebuild target option node
> > >       once optimization node gets rebuilt.
> > >
> > > gcc/testsuite/ChangeLog:
> > >
> > >       * gcc.dg/lto/pr105459_0.c: New test.
> > > ---
> > >  gcc/ipa-inline-transform.cc           | 50 +++++++++++++++++++++++++--
> > >  gcc/testsuite/gcc.dg/lto/pr105459_0.c | 35 +++++++++++++++++++
> > >  2 files changed, 83 insertions(+), 2 deletions(-)
> > >  create mode 100644 gcc/testsuite/gcc.dg/lto/pr105459_0.c
> > >
> > > diff --git a/gcc/ipa-inline-transform.cc b/gcc/ipa-inline-transform.cc
> > > index 07288e57c73..edba58377f4 100644
> > > --- a/gcc/ipa-inline-transform.cc
> > > +++ b/gcc/ipa-inline-transform.cc
> > > @@ -52,6 +52,7 @@ along with GCC; see the file COPYING3.  If not see
> > >  #include "ipa-modref.h"
> > >  #include "symtab-thunks.h"
> > >  #include "symtab-clones.h"
> > > +#include "target.h"
> > >
> > >  int ncalls_inlined;
> > >  int nfunctions_inlined;
> > > @@ -469,8 +470,53 @@ inline_call (struct cgraph_edge *e, bool update_original,
> > >      }
> > >
> > >    /* Reload global optimization flags.  */
> > > -  if (reload_optimization_node && DECL_STRUCT_FUNCTION (to->decl) == cfun)
> > > -    set_cfun (cfun, true);
> > > +  if (reload_optimization_node)
> > > +    {
> > > +      /* Only need to check and update target option node
> > > +      when target_option_default_node is not NULL.  */
> > > +      if (target_option_default_node)
> > > +     {
> > > +       /* Save the current context for optimization and target option
> > > +          node.  */
> > > +       tree old_optimize
> > > +         = build_optimization_node (&global_options, &global_options_set);
> > > +       tree old_target_opt
> > > +         = build_target_option_node (&global_options, &global_options_set);
> > > +
> > > +       /* Restore optimization with new optimizatin node.  */
> > > +       tree new_optimize = DECL_FUNCTION_SPECIFIC_OPTIMIZATION (to->decl);
> > > +       if (old_optimize != new_optimize)
> > > +         cl_optimization_restore (&global_options, &global_options_set,
> > > +                                  TREE_OPTIMIZATION (new_optimize));
> > > +
> > > +       /* Restore target option with the one from caller fndecl.  */
> > > +       tree cur_target_opt = DECL_FUNCTION_SPECIFIC_TARGET (to->decl);
> > > +       if (!cur_target_opt)
> > > +         cur_target_opt = target_option_default_node;
> > > +       cl_target_option_restore (&global_options, &global_options_set,
> > > +                                 TREE_TARGET_OPTION (cur_target_opt));
> > > +
> > > +       /* Update target option as optimization changes.  */
> > > +       targetm.target_option.override ();
> > > +
> > > +       /* Rebuild target option node for caller fndecl and replace
> > > +          with it if the node changes.  */
> > > +       tree new_target_opt
> > > +         = build_target_option_node (&global_options, &global_options_set);
> > > +       if (cur_target_opt != new_target_opt)
> > > +         DECL_FUNCTION_SPECIFIC_TARGET (to->decl) = new_target_opt;
> > > +
> > > +       /* Restore the context with previous saved nodes.  */
> > > +       if (old_optimize != new_optimize)
> > > +         cl_optimization_restore (&global_options, &global_options_set,
> > > +                                  TREE_OPTIMIZATION (old_optimize));
> > > +       cl_target_option_restore (&global_options, &global_options_set,
> > > +                                 TREE_TARGET_OPTION (old_target_opt));
> > > +     }
> > > +
> > > +      if (DECL_STRUCT_FUNCTION (to->decl) == cfun)
> > > +     set_cfun (cfun, true);
> > > +    }
> > >
> > >    /* If aliases are involved, redirect edge to the actual destination and
> > >       possibly remove the aliases.  */
> > > diff --git a/gcc/testsuite/gcc.dg/lto/pr105459_0.c b/gcc/testsuite/gcc.dg/lto/pr105459_0.c
> > > new file mode 100644
> > > index 00000000000..c799e6ef23d
> > > --- /dev/null
> > > +++ b/gcc/testsuite/gcc.dg/lto/pr105459_0.c
> > > @@ -0,0 +1,35 @@
> > > +/* { dg-lto-do link } */
> > > +/* { dg-lto-options { { -flto -O1 } } } */
> > > +
> > > +double m;
> > > +int n;
> > > +
> > > +__attribute__ ((optimize ("-funsafe-math-optimizations")))
> > > +void
> > > +bar (int x)
> > > +{
> > > +  n = x;
> > > +  m = n;
> > > +}
> > > +
> > > +__attribute__ ((flatten))
> > > +void
> > > +foo (int x)
> > > +{
> > > +  bar (x);
> > > +}
> > > +
> > > +void
> > > +quux (void)
> > > +{
> > > +  ++n;
> > > +}
> > > +
> > > +int
> > > +main (void)
> > > +{
> > > +  foo (0);
> > > +  quux ();
> > > +
> > > +  return 0;
> > > +}
> > > --
> > > 2.27.0




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