[Bug c++/97468] New: gcc crashes when using __may_alias__ attribute

[Bug c++/97468] New: gcc crashes when using __may_alias__ attribute

[tangyixuan at mail dot dlut.edu.cn]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97468

            Bug ID: 97468
           Summary: gcc crashes when using __may_alias__ attribute
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: tangyixuan at mail dot dlut.edu.cn
  Target Milestone: ---

Hi, the following code uses '__attribute__ ((__may_alias__))' to alias a struct
'S' to 'a'. However, gcc crashes at compilation time while clang successfully
compiles.

gcc doc:
https://gcc.gnu.org/onlinedocs/gcc-10.2.0/gcc/Common-Type-Attributes.html#Common-Type-Attributes
'Accesses through pointers to types with this attribute are not subject to
type-based alias analysis, but are instead assumed to be able to alias any
other type of objects.'

$ cat s.cpp

template<typename T> struct S{};
auto __attribute__ ((__may_alias__)) a=S<int>{};

$ g++ -c s.cpp
s.cpp:2:38: internal compiler error: in layout_type, at stor-layout.c:2618
   2 | auto __attribute__ ((__may_alias__)) a=S<int>{};
      |                                      ^
0x62d384 layout_type(tree_node*)
        ../../gcc-11-20201011/gcc/stor-layout.c:2618
0xebaf34 type_hash_canon(unsigned int, tree_node*)
        ../../gcc-11-20201011/gcc/tree.c:7140
0x7e6beb build_type_attribute_qual_variant(tree_node*, tree_node*, int)
        ../../gcc-11-20201011/gcc/attribs.c:1166
0x7e8702 build_type_attribute_variant(tree_node*, tree_node*)
        ../../gcc-11-20201011/gcc/attribs.c:1377
0x7e8702 decl_attributes(tree_node**, tree_node*, int, tree_node*)
        ../../gcc-11-20201011/gcc/attribs.c:794
0x6d9e93 cplus_decl_attributes(tree_node**, tree_node*, int)
        ../../gcc-11-20201011/gcc/cp/decl2.c:1595
0x6cd1bf start_decl(cp_declarator const*, cp_decl_specifier_seq*, int,
tree_node*, tree_node*, tree_node**)
        ../../gcc-11-20201011/gcc/cp/decl.c:5267
0x7590ce cp_parser_init_declarator
        ../../gcc-11-20201011/gcc/cp/parser.c:20936
0x73a65c cp_parser_simple_declaration
        ../../gcc-11-20201011/gcc/cp/parser.c:13878
0x7630a6 cp_parser_declaration
        ../../gcc-11-20201011/gcc/cp/parser.c:13577
0x7636dd cp_parser_translation_unit
        ../../gcc-11-20201011/gcc/cp/parser.c:4793
0x7636dd c_parse_file()
        ../../gcc-11-20201011/gcc/cp/parser.c:44172
0x82f13d c_common_parse_file()
        ../../gcc-11-20201011/gcc/c-family/c-opts.c:1188
Please submit a full bug report,
with preprocessed source if appropriate.
Please include the complete backtrace with any bug report.
See <https://gcc.gnu.org/bugs/> for instructions.

[Bug c++/97468] gcc crashes when using __may_alias__ attribute

[marxin at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97468

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |marxin at gcc dot gnu.org
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2020-10-19
     Ever confirmed|0                           |1

--- Comment #1 from Martin Liška <marxin at gcc dot gnu.org> ---
Confirmed, it's at least as old as 4.8.0.

[Bug c++/97468] gcc crashes when using __may_alias__ attribute

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97468

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |ice-on-valid-code

--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
#1  0x00000000016e9d82 in layout_type (
    type=<template_type_parm 0x7ffff696adc8 auto>)
    at /home/rguenther/src/gcc2/gcc/stor-layout.c:2618

but of course calling layout_type from type_hash_canon is quite fishy as
we'll end up layouting a template_type_parm here ... now, feeding this
to type_hash_canon is fishy as well so the FE should probably not call
any of the attribute handlers on those ...

tree
type_hash_canon (unsigned int hashcode, tree type)
{
  type_hash in;
  type_hash **loc;

  /* The hash table only contains main variants, so ensure that's what we're
     being passed.  */
  gcc_assert (TYPE_MAIN_VARIANT (type) == type);

  /* The TYPE_ALIGN field of a type is set by layout_type(), so we
     must call that routine before comparing TYPE_ALIGNs.  */
  layout_type (type);

[Bug c++/97468] gcc crashes when using __may_alias__ attribute

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97468

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

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

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Dup of bug 89867.

*** This bug has been marked as a duplicate of bug 89867 ***