Re: [PATCH] c++: local class memfn synth from noexcept context [PR113063]

[Jason Merrill]

On 8/20/24 11:52 AM, Patrick Palka wrote:

Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look
OK for trunk only?

OK.

-- >8 --

Extending the PR113063 testcase to additionally constant evaluate the <=>
expression causes us to trip over the assert in cxx_eval_call_expression

   /* We used to shortcut trivial constructor/op= here, but nowadays
      we can only get a trivial function here with -fno-elide-constructors.  */
   gcc_checking_assert (!trivial_fn_p (fun)
                        || !flag_elide_constructors
                        /* We don't elide constructors when processing
                           a noexcept-expression.  */
                        || cp_noexcept_operand);

since the local class's <=> was first used and therefore synthesized in
a noexcept context and so its definition contains unelided trivial
constructors.

This patch fixes this by clearing cp_noexcept_operand alongside
cp_unevaluated_context in the local class case.

        PR c++/113063

gcc/cp/ChangeLog:

        * name-lookup.cc (local_state_t): Clear and restore
        cp_noexcept_operand as well.

gcc/testsuite/ChangeLog:

        * g++.dg/cpp2a/spaceship-synth16.C: Also constant evaluate the
        <=> expression.
        * g++.dg/cpp2a/spaceship-synth16a.C: Likewise.
---
  gcc/cp/name-lookup.cc                           | 4 ++++
  gcc/testsuite/g++.dg/cpp2a/spaceship-synth16.C  | 1 +
  gcc/testsuite/g++.dg/cpp2a/spaceship-synth16a.C | 1 +
  3 files changed, 6 insertions(+)

diff --git a/gcc/cp/name-lookup.cc b/gcc/cp/name-lookup.cc
index 70ad4cbf3b5..6fb664b0082 100644
--- a/gcc/cp/name-lookup.cc
+++ b/gcc/cp/name-lookup.cc
@@ -8775,6 +8775,7 @@ struct local_state_t
  {
    int cp_unevaluated_operand;
    int c_inhibit_evaluation_warnings;
+  int saved_cp_noexcept_operand;

static local_state_t

    save_and_clear ()
@@ -8784,6 +8785,8 @@ struct local_state_t
      ::cp_unevaluated_operand = 0;
      s.c_inhibit_evaluation_warnings = ::c_inhibit_evaluation_warnings;
      ::c_inhibit_evaluation_warnings = 0;
+    s.saved_cp_noexcept_operand = cp_noexcept_operand;
+    cp_noexcept_operand = 0;
      return s;
    }

@@ -8792,6 +8795,7 @@ struct local_state_t

    {
      ::cp_unevaluated_operand = this->cp_unevaluated_operand;
      ::c_inhibit_evaluation_warnings = this->c_inhibit_evaluation_warnings;
+    cp_noexcept_operand = this->saved_cp_noexcept_operand;
    }
  };

diff --git a/gcc/testsuite/g++.dg/cpp2a/spaceship-synth16.C b/gcc/testsuite/g++.dg/cpp2a/spaceship-synth16.C

index 37a183de0f5..7dbe7e1db75 100644
--- a/gcc/testsuite/g++.dg/cpp2a/spaceship-synth16.C
+++ b/gcc/testsuite/g++.dg/cpp2a/spaceship-synth16.C
@@ -10,4 +10,5 @@ int main() {
    X x;
    static_assert(noexcept(x <=> x));
    x <=> x;
+  constexpr auto r = x <=> x;
  }
diff --git a/gcc/testsuite/g++.dg/cpp2a/spaceship-synth16a.C 
b/gcc/testsuite/g++.dg/cpp2a/spaceship-synth16a.C
index 68388a680b2..bc0e7a54b7e 100644
--- a/gcc/testsuite/g++.dg/cpp2a/spaceship-synth16a.C
+++ b/gcc/testsuite/g++.dg/cpp2a/spaceship-synth16a.C
@@ -13,4 +13,5 @@ int main() {
    X x;
    static_assert(noexcept(x <=> x));
    x <=> x;
+  constexpr auto r = X{} <=> X{};
  }