[Bug c++/102881] New: gcc totally broken when trailing return type combine with decltype lambda

[Bug c++/102881] New: gcc totally broken when trailing return type combine with decltype lambda

[hewillk at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102881

            Bug ID: 102881
           Summary: gcc totally broken when trailing return type combine
                    with decltype lambda
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: hewillk at gmail dot com
  Target Milestone: ---

template<int N>
using R = decltype([] { return 0; }());

template <int N>
auto you_can_see_me() -> R<N> {
  return {};
}

int main() {
  you_can_see_me<0>();
}

GCC rejects with:

<source>:10:3: error: 'you_can_see_me' was not declared in this scope
   10 |   you_can_see_me<0>();
      |   ^~~~~~~~~~~~~~~~~

https://godbolt.org/z/7WEsjjscT

[Bug c++/102881] gcc totally broken when trailing return type combine with decltype lambda

[hewillk at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102881

--- Comment #1 from 康桓瑋 <hewillk at gmail dot com> ---
(In reply to 康桓瑋 from comment #0)
> template<int N>
> using R = decltype([] { return 0; }());
> 
> template <int N>
> auto you_can_see_me() -> R<N> {
>   return {};
> }
> 
> int main() {
>   you_can_see_me<0>();
> }
> 
> GCC rejects with:
> 
> <source>:10:3: error: 'you_can_see_me' was not declared in this scope
>    10 |   you_can_see_me<0>();
>       |   ^~~~~~~~~~~~~~~~~
> 
> https://godbolt.org/z/7WEsjjscT

Even broken when there is no trailing return type:

#include <concepts>

template<class>
struct O {};

template<std::size_t>
using R = decltype([] { return O<int>{}; }());

template <int N>
constexpr R<N> get_variant() { return {}; }

static_assert(std::same_as<R<0>, O<int>>);
auto x = get_variant<0>();
static_assert(!std::same_as<decltype(x), O<int>>);
static_assert(std::same_as<decltype(x), int>);

https://godbolt.org/z/4bKccTEe5

[Bug c++/102881] gcc totally broken when trailing return type combine with decltype lambda

[vanyacpp at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102881

Ivan Sorokin <vanyacpp at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |vanyacpp at gmail dot com

--- Comment #2 from Ivan Sorokin <vanyacpp at gmail dot com> ---
PR92707 also features lambda inside decltype. Perhaps they are related.

[Bug c++/102881] gcc totally broken when trailing return type combine with decltype lambda

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102881

--- Comment #3 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Uros Bizjak <uros@gcc.gnu.org>:

https://gcc.gnu.org/g:7eb961d83b0eda53aeb1cfaacdc367e1952de613

commit r12-5700-g7eb961d83b0eda53aeb1cfaacdc367e1952de613
Author: Uros Bizjak <ubizjak@gmail.com>
Date:   Wed Dec 1 23:01:09 2021 +0100

    i386: Improve V8HI and V8HF inserts [PR102811]

    Introduce vec_set_0 pattern for V8HI and V8HF modes to implement scalar
    element 0 inserts to from a GP register, SSE register or memory.  Also
    add V8HI and V8HF AVX2 (x,x,x) alternative to PINSR insn pattern, which is
    split after reload to a sequence of PBROADCASTW and PBLENDW.

    The V8HF inserts from memory improve from:

    -       vpbroadcastw    4(%esp), %xmm1
    -       vpblendw        $16, %xmm1, %xmm0, %xmm0
    +       vpinsrw $4, 4(%esp), %xmm0, %xmm0

    and V8HF inserts from SSE register to element 0 improve from:

            vpxor   %xmm2, %xmm2, %xmm2
    -       vpbroadcastw    %xmm0, %xmm0
            vpblendw        $1, %xmm0, %xmm2, %xmm0

    Based on the above improvements, the register allocator is able to
determine
    the optimal instruction (or instruction sequence) based on the register set
    of the input value, so there is no need to manually expand V8HI and V8HF
    inserts to the sequence of VEC_DUPLICATE and VEC_MERGE RTXes.

    2021-12-01  Uroš Bizjak  <ubizjak@gmail.com>

    gcc/ChangeLog:

            PR target/102811
            * config/i386/sse.md (VI2F): Remove mode iterator.
            (VI2F_256_512): New mode iterator.
            (vec_set<V8_128:mode>_0): New insn pattern.
            (vec_set<VI2F_256_512:mode>_0>): Rename from
vec_set<VI2F:mode>mode.
            Use VI2F_256_512 mode iterator instead of VI2F.
            (*axv512fp16_movsh): Remove.
            (<sse2p4_1>_pinsr<ssemodesuffix>): Add (x,x,x) AVX2 alternative.
            Do not disable V8HF mode insn on AVX2 targets.
            (pinsrw -> pbroadcast + pblendw peephole2): New peephole.
            (pinsrw -> pbroadcast + pblendw splitter): New post-reload
splitter.
            * config/i386/i386.md (extendhfsf): Call gen_vec_setv8hf_0.
            * config/i386/i386-expand.c (ix86_expand_vector_set)
            <case E_V8HFmode>: Use vec_merge path for TARGET_AVX2.

    gcc/testsuite/ChangeLog:

            PR target/102881
            * gcc.target/i386/pr102811-1.c: New test.
            * gcc.target/i386/avx512fp16-1c.c (dg-final): Update
            scan-assembler-times scan strings for ia32 targets.
            * gcc.target/i386/pr102327-1.c (dg-final): Ditto.
            * gcc.target/i386/pr102811.c: Rename from ...
            * gcc.target/i386/avx512vl-vcvtps2ph-pr102811.c: ... this.

[Bug c++/102881] gcc totally broken when trailing return type combine with decltype lambda

[ubizjak at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102881

--- Comment #4 from Uroš Bizjak <ubizjak at gmail dot com> ---
> The master branch has been updated by Uros Bizjak <uros@gcc.gnu.org>:

Oops, wrong PR number...

[Bug c++/102881] gcc totally broken when trailing return type combine with decltype lambda

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102881

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jakub at gcc dot gnu.org,
                   |                            |ppalka at gcc dot gnu.org

--- Comment #5 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Seems foo gets silently (because of tentative parser in
cp_parser_late_return_type_opt -> cp_parser_trailing_type_id ->
cp_parser_type_id_1 -> cp_parser_type_specifier_seq -> cp_parser_type_specifier
-> cp_parser_simple_type_specifier
19684         /* Don't gobble tokens or issue error messages if this is an
19685            optional type-specifier.  */
19686         if (flags & CP_PARSER_FLAGS_OPTIONAL)
19687           cp_parser_parse_tentatively (parser);
) late_return of error_mark_node, and that then causes pushdecl not to happen
and so it isn't found.  But getting lost in why the type specifier parsing
failed...

[Bug c++/102881] gcc totally broken when trailing return type combine with decltype lambda

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102881

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |FIXED
   Target Milestone|---                         |14.0
             Status|UNCONFIRMED                 |RESOLVED

--- Comment #6 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Fixed for GCC 14 by the recent lambda template patches.