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From: "jbassett271 at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/101043] New: ICE in check_noexcept_r for lambda conditional
 noexcept via requires expression
Date: Sun, 13 Jun 2021 01:46:19 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D101043

            Bug ID: 101043
           Summary: ICE in check_noexcept_r for lambda conditional
                    noexcept via requires expression
           Product: gcc
           Version: 10.3.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jbassett271 at gmail dot com
  Target Milestone: ---

GCC has an internal compiler error for requires expressions inside the noex=
cept
clause of a lambda inside a templated function:

https://godbolt.org/z/oWhq9sf8M


template <typename T>
struct set {
  bool contains(T const&) const { return true; }
};

template <typename T>
void intersect(set<T> const& lhs, set<T> const& rhs) {
  auto f =3D [&]<typename T1>(T1&& _1) noexcept(requires {
    { rhs.contains(_1) } noexcept;
  }) {
      return rhs.contains(_1);
  };
}

int main() {
  set<int> lhs;
  set<int> rhs;
  intersect(lhs, rhs);
}


Error message:

<source>: In instantiation of 'void intersect(const set<T>&, const set<T>&)
[with T =3D int]':
<source>:18:21:   required from here
<source>:9:7: internal compiler error: in check_noexcept_r, at cp/except.c:=
1123
    9 |     { rhs.contains(_1) } noexcept;
      |     ~~^~~~~~~~~~~~~~~~~~~~~~~~~~~
Please submit a full bug report,
with preprocessed source if appropriate.
See <https://gcc.gnu.org/bugs/> for instructions.


The commandline arguments, according to the Compiler Explorer link (cleaned=
 a
little):

-g -o output.s -masm=3Dintel -S -fdiagnostics-color=3Dalways -std=3Dc++20 e=
xample.cpp

Clang compiles this fine.

I was able to replicate this bug in GCC versions 10.1, 10.2, 10.3, and 11.1=
.=