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From: "janschultke at googlemail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/113274] New: Memoization in template parameters is overly
 aggressive; false memoization for const pointers
Date: Mon, 08 Jan 2024 14:50:35 +0000
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X-Bugzilla-Type: new
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X-Bugzilla-Product: gcc
X-Bugzilla-Component: c++
X-Bugzilla-Version: 14.0
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X-Bugzilla-Severity: normal
X-Bugzilla-Who: janschultke at googlemail dot com
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X-Bugzilla-Priority: P3
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D113274

            Bug ID: 113274
           Summary: Memoization in template parameters is overly
                    aggressive; false memoization for const pointers
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: janschultke at googlemail dot com
  Target Milestone: ---

## Minimal Reproducible Example (https://godbolt.org/z/Y7Kr9o546)

template <auto>
struct A {
    static constexpr bool value =3D false;
};

template <auto p>
  requires __is_same(decltype(p), int*)
struct A<p> {
    static constexpr bool value =3D false;
};

int x =3D 0;
//static_assert( A<&x>::value );
static_assert( A<const_cast<const int*>(&x)>::value =3D=3D false );

## Explanation

Uncommenting the first static_assert causes compilation failure of the seco=
nd
static_assert.
This should definitely not happen, as the following instantiations should be
distinct:

- A<(int*) &x>
- A<(const int*) &x>

GCC aggressively memoizes the first instantiation in A<&x>, which results in
the subsequent A<(const int*)&x>::value being identical, even though it sho=
uld
not be.=