[Bug lto/105399] New: [12 Regression] -O2/-Ofast -flto ICEs as internal compiler error: verify_cgraph_node failed

[Bug lto/105399] New: [12 Regression] -O2/-Ofast -flto ICEs as internal compiler error: verify_cgraph_node failed

[slyfox at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105399

            Bug ID: 105399
           Summary: [12 Regression] -O2/-Ofast -flto ICEs as internal
                    compiler error: verify_cgraph_node failed
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: lto
          Assignee: unassigned at gcc dot gnu.org
          Reporter: slyfox at gcc dot gnu.org
                CC: marxin at gcc dot gnu.org
  Target Milestone: ---

Found as an ICE on ncnn project. Minimized example:

    // cat bug.cpp.cpp
    struct S {
      S();
    };
    S::S() {}

$ g++ -fPIC -flto -Ofast         -o bug.o      -c bug.cpp.cpp
$ g++ -fPIC -flto -O2    -shared -o libncnn.so    bug.o

lto1: error: semantic interposition mismatch
_ZN1SC1Ev/2 (__ct_comp ) @0x7f8bd1e14110
  Type: function definition analyzed alias
  Visibility: externally_visible prevailing_def_ironly_exp public
  References: _ZN1SC2Ev/1 (alias)
  Referring:
  Read from file: bug.o
  Unit id: 1
  Function flags:
  Called by:
  Calls:
during IPA pass: modref
lto1: internal compiler error: verify_cgraph_node failed
0x97eec0 cgraph_node::verify_node()
        ../../gcc-12-20220424/gcc/cgraph.cc:3874
0x96eb84 symtab_node::verify()
        ../../gcc-12-20220424/gcc/symtab.cc:1359
0x96fcf7 symtab_node::verify_symtab_nodes()
        ../../gcc-12-20220424/gcc/symtab.cc:1387
0xc13224 symtab_node::checking_verify_symtab_nodes()
        ../../gcc-12-20220424/gcc/cgraph.h:682
0xc13224 symbol_table::remove_unreachable_nodes(_IO_FILE*)
        ../../gcc-12-20220424/gcc/ipa.cc:679
0x8f57f5 read_cgraph_and_symbols(unsigned int, char const**)
        ../../gcc-12-20220424/gcc/lto/lto-common.cc:2960
0x8dcdb2 lto_main()
        ../../gcc-12-20220424/gcc/lto/lto.cc:626

$ g++ -v
Using built-in specs.
COLLECT_GCC=/<<NIX>>/gcc-debug-12.0.0/bin/g++
COLLECT_LTO_WRAPPER=/<<NIX>>/gcc-debug-12.0.0/libexec/gcc/x86_64-unknown-linux-gnu/12.0.1/lto-wrapper
Target: x86_64-unknown-linux-gnu
Configured with:
Thread model: posix
Supported LTO compression algorithms: zlib
gcc version 12.0.1 20220424 (experimental) (GCC)

[Bug lto/105399] [12 Regression] -O2/-Ofast -flto ICEs as internal compiler error: verify_cgraph_node failed

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105399

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |hubicka at gcc dot gnu.org,
                   |                            |jakub at gcc dot gnu.org
   Target Milestone|---                         |12.0

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
IIRC Jakub fixed a similar bug recently, and Honza had followup comments.

[Bug lto/105399] [12 Regression] -O2/-Ofast -flto ICEs as internal compiler error: verify_cgraph_node failed

[marxin at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105399

Martin Liška <marxin at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2022-04-27
     Ever confirmed|0                           |1

[Bug lto/105399] [12 Regression] -O2/-Ofast -flto ICEs as internal compiler error: verify_cgraph_node failed

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105399

--- Comment #2 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Because of -Ofast initial compilation, opt_for_fn (decl,
flag_semantic_interposition) is false for all the decls for which a cgraph node
is created, but they have NULL DECL_FUNCTION_SPECIFIC_OPTIMIZATION, and thus
they look up the bit in optimization_default_node.
That results in node->semantic_interposition to be 0 as well.
Next comes free_lang_data_in_decl, which does:

  if (TREE_CODE (decl) == FUNCTION_DECL)
...
      if (gimple_has_body_p (decl) || (node && node->thunk))
...
          if (!DECL_FUNCTION_SPECIFIC_OPTIMIZATION (decl))
            DECL_FUNCTION_SPECIFIC_OPTIMIZATION (decl)
              = optimization_default_node;
Now, free_lang_data_in_decl is called on 3 FUNCTION_DECLs,
_ZN1SC1Ev aka __ct_comp, which is node->alias && !node->semantic_interposition,
gimple_has_body_p (decl) is false for it and we don't do anything.
Next it is called on _ZN1SC4Ev aka __ct, which has NULL node and
gimple_has_body_p (decl) is false for it too.
Last it is called for _ZN1SC2Ev aka __ct_base, which is !node->alias &&
!node->semantic_interposition, gimple_has_body_p (decl) is true and we set
DECL_FUNCTION_SPECIFIC_OPTIMIZATION (decl) to optimization_default_node.
Then we stream all this out, and stream it back, except that
optimization_default_node is one for -O2 with x_flag_semantic_interposition set
for it.
_ZN1SC2Ev passes the verification, node->semantic_interposition is false
and opt_for_fn (decl, flag_semantic_interposition) is false as well.
But for _ZN1SC1Ev we ICE on:
  if (definition && externally_visible
      && semantic_interposition
         != opt_for_fn (decl, flag_semantic_interposition))
    {
      error ("semantic interposition mismatch");
      error_found = true;
    }
That is because for aliases which don't have a body, we kept
DECL_FUNCTION_SPECIFIC_OPTIMIZATION (decl) NULL.
One way to fix this would be
-  if (definition && externally_visible
+  if (definition
+      && externally_visible
+      && (!alias || thunk)
       && semantic_interposition
          != opt_for_fn (decl, flag_semantic_interposition))
     {
       error ("semantic interposition mismatch");
       error_found = true;
     }
i.e. don't bother verification of mismatches for aliases.  Another would be
to adjust DECL_FUNCTION_SPECIFIC_OPTIMIZATION (decl) in free_lang_data_in_decl
even for aliases.

[Bug lto/105399] [12 Regression] -O2/-Ofast -flto ICEs as internal compiler error: verify_cgraph_node failed

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105399

--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
I can't easily bisect when this started but bet with
r12-5412-g458d2c689963d8461d84670a3d8988cd6ecbfd81
or later.
Not sure if this should be P1 because it is ice-checking only, in release
compilers flag_checking defaults to 0 and so it isn't done unless -fchecking is
used.

[Bug lto/105399] [12 Regression] -O2/-Ofast -flto ICEs as internal compiler error: verify_cgraph_node failed

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105399

--- Comment #4 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Created attachment 52889
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=52889&action=edit
gcc12-pr105399.patch

One possible untested fix.

[Bug lto/105399] [12 Regression] -O2/-Ofast -flto ICEs as internal compiler error: verify_cgraph_node failed

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105399

--- Comment #5 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jakub Jelinek <jakub@gcc.gnu.org>:

https://gcc.gnu.org/g:b85e79dce149df68b92ef63ca2a40ff1dfa61396

commit r12-8312-gb85e79dce149df68b92ef63ca2a40ff1dfa61396
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Thu Apr 28 15:45:33 2022 +0200

    cgraph: Don't verify semantic_interposition flag for aliases [PR105399]

    The following testcase ICEs, because the ctors during cc1plus all have
    !opt_for_fn (decl, flag_semantic_interposition) - they have NULL
    DECL_FUNCTION_SPECIFIC_OPTIMIZATION (decl) and optimization_default_node
    is for -Ofast and so has flag_semantic_interposition cleared.
    During free lang data, we set DECL_FUNCTION_SPECIFIC_OPTIMIZATION (decl)
    for the ctor which has body (or for thunks), but don't touch it for
    aliases.
    During lto1 optimization_default_node reflects the lto1 flags which
    are -O2 rather than -Ofast and so has flag_semantic_interposition
    set, for the ctor which has body that makes no difference, but as the
    alias doesn't still have DECL_FUNCTION_SPECIFIC_OPTIMIZATION (decl) set,
    we now trigger this verification check.

    The following patch just doesn't verify it for aliases during lto1.
    Another possibility would be to set DECL_FUNCTION_SPECIFIC_OPTIMIZATION
(decl)
    during free lang data even for aliases.

    2022-04-28  Jakub Jelinek  <jakub@redhat.com>

            PR lto/105399
            * cgraph.cc (cgraph_node::verify_node): Don't verify
            semantic_interposition flag against
            opt_for_fn (decl, flag_semantic_interposition) for aliases in lto1.

            * g++.dg/lto/pr105399_0.C: New test.

[Bug lto/105399] [12 Regression] -O2/-Ofast -flto ICEs as internal compiler error: verify_cgraph_node failed

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105399

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |FIXED
             Status|NEW                         |RESOLVED

--- Comment #6 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Fixed.