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

["tangyixuan at mail dot dlut.edu.cn" <gcc-bugzilla@gcc.gnu.org>]

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
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