From: Jan Hubicka <hubicka@kam.mff.cuni.cz>
To: Richard Biener <richard.guenther@gmail.com>
Cc: "Kewen.Lin" <linkw@linux.ibm.com>,
Jakub Jelinek <jakub@redhat.com>,
GCC Patches <gcc-patches@gcc.gnu.org>,
mliska@suse.cz
Subject: Re: PING^1 [PATCH] inline: Rebuild target option node for caller [PR105459]
Date: Fri, 1 Jul 2022 11:20:57 +0200 [thread overview]
Message-ID: <Yr68eTv/1KZD15Kk@kam.mff.cuni.cz> (raw)
In-Reply-To: <CAFiYyc2vGjcQrGbt+VhQEjvaGraFAM+uVy7N3Tn1a_XgoPsMdw@mail.gmail.com>
> 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
next prev parent reply other threads:[~2022-07-01 9:20 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-06-06 6:20 Kewen.Lin
2022-06-23 2:03 ` PING^1 " Kewen.Lin
2022-07-01 8:40 ` Richard Biener
2022-07-01 9:20 ` Jan Hubicka [this message]
2022-07-01 12:09 ` Richard Biener
2022-07-01 9:42 ` Kewen.Lin
2022-07-08 11:37 ` Martin Liška
2022-07-11 3:37 ` Kewen.Lin
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