[gcc/devel/ranger] c++: Don't synthesize sfk_comparison method multiple times [PR94907]

[Aldy Hernandez]

https://gcc.gnu.org/g:25ee2155ead87a5ea1c152a29341ee1e3275d706

commit 25ee2155ead87a5ea1c152a29341ee1e3275d706
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Wed May 6 23:36:31 2020 +0200

    c++: Don't synthesize sfk_comparison method multiple times [PR94907]
    
    On the following testcase we ICE, because synthesize_method is called twice
    on the same sfk_comparison method fndecl, the first time it works fine
    because start_preparsed_function in that case sets both
    current_function_decl and cfun, but second time it is called it only sets
    the former and keeps cfun NULL, so we ICE when trying to store
    current_function_returns_value.
    I think it is just wrong to call synthesize_method multiple times, and most
    synthesize_method callers avoid that by not calling it if DECL_INITIAL is
    already set, so this patch does that too.
    
    2020-05-06  Jakub Jelinek  <jakub@redhat.com>
    
            PR c++/94907
            * method.c (defaulted_late_check): Don't call synthesize_method
            on constexpr sfk_comparison if it has been called on it already.
    
            * g++.dg/cpp2a/spaceship-synth8.C: New test.

Diff:
---
 gcc/cp/ChangeLog                              |  6 ++++++
 gcc/cp/method.c                               |  2 +-
 gcc/testsuite/ChangeLog                       |  5 +++++
 gcc/testsuite/g++.dg/cpp2a/spaceship-synth8.C | 12 ++++++++++++
 4 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/gcc/cp/ChangeLog b/gcc/cp/ChangeLog
index 7e41433707e..32bb9f5dfa8 100644
--- a/gcc/cp/ChangeLog
+++ b/gcc/cp/ChangeLog
@@ -1,3 +1,9 @@
+2020-05-06  Jakub Jelinek  <jakub@redhat.com>
+
+	PR c++/94907
+	* method.c (defaulted_late_check): Don't call synthesize_method
+	on constexpr sfk_comparison if it has been called on it already.
+
 2020-05-06  Nathan Sidwell  <nathan@acm.org>
 
 	PR c++/94946
diff --git a/gcc/cp/method.c b/gcc/cp/method.c
index fb2dd47013f..47f96aa845e 100644
--- a/gcc/cp/method.c
+++ b/gcc/cp/method.c
@@ -2939,7 +2939,7 @@ defaulted_late_check (tree fn)
     {
       /* If the function was declared constexpr, check that the definition
 	 qualifies.  Otherwise we can define the function lazily.  */
-      if (DECL_DECLARED_CONSTEXPR_P (fn))
+      if (DECL_DECLARED_CONSTEXPR_P (fn) && !DECL_INITIAL (fn))
 	synthesize_method (fn);
       return;
     }
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 6aa43787122..a2c0e8571d9 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,8 @@
+2020-05-06  Jakub Jelinek  <jakub@redhat.com>
+
+	PR c++/94907
+	* g++.dg/cpp2a/spaceship-synth8.C: New test.
+
 2020-05-06  qing zhao  <qing.zhao@oracle.com>
 
 	PR c/94230
diff --git a/gcc/testsuite/g++.dg/cpp2a/spaceship-synth8.C b/gcc/testsuite/g++.dg/cpp2a/spaceship-synth8.C
new file mode 100644
index 00000000000..d0d68c7fa6f
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/spaceship-synth8.C
@@ -0,0 +1,12 @@
+// PR c++/94907
+// { dg-do compile { target c++2a } }
+
+namespace std { struct strong_ordering { }; }
+
+struct E;
+struct D {
+  virtual std::strong_ordering operator<=>(const struct E&) const = 0;
+};
+struct E : D {
+  std::strong_ordering operator<=>(const E&) const override = default;
+};