[gcc(refs/users/aoliva/heads/testme)] c++: tolerate cdtors returning this in constexpr

[gcc(refs/users/aoliva/heads/testme)] c++: tolerate cdtors returning this in constexpr

[Alexandre Oliva]

https://gcc.gnu.org/g:7761bd3d52d97dd9326f168ac02d6f119ca17813

commit 7761bd3d52d97dd9326f168ac02d6f119ca17813
Author: Alexandre Oliva <oliva@adacore.com>
Date:   Wed Apr 6 15:22:44 2022 -0300

    c++: tolerate cdtors returning this in constexpr
    
    On targets that return this from cdtors, cxx_eval_call_expression may
    flag flowing off the end of a dtor.  That's preempted for ctors, and
    avoided entirely when dtors return void, but when they return this,
    the return value should be conceptually disregarded, without making
    room for such internal ABI details to make a program ill-formed, as in
    g++.dg/cpp2a/constexpr-dtor12.C on arm-eabi.
    
    
    for  gcc/cp/ChangeLog
    
            * constexpr.cc (cxx_eval_call_expression): Disregard dtor
            result.

Diff:
---
 gcc/cp/constexpr.cc | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/gcc/cp/constexpr.cc b/gcc/cp/constexpr.cc
index 9c40b051574..d8bc864ae6b 100644
--- a/gcc/cp/constexpr.cc
+++ b/gcc/cp/constexpr.cc
@@ -2889,7 +2889,8 @@ cxx_eval_call_expression (const constexpr_ctx *ctx, tree t,
 	  else
 	    {
 	      result = *ctx->global->values.get (res);
-	      if (result == NULL_TREE && !*non_constant_p)
+	      if (result == NULL_TREE && !*non_constant_p
+		  && !DECL_DESTRUCTOR_P (fun))
 		{
 		  if (!ctx->quiet)
 		    error ("%<constexpr%> call flows off the end "