[gcc r13-4433] c++: small contracts fixes

[Jason Merrill <jason@gcc.gnu.org>]

https://gcc.gnu.org/g:4304e09a1617bcf1c87f5bc96017ae5017379d75

commit r13-4433-g4304e09a1617bcf1c87f5bc96017ae5017379d75
Author: Jason Merrill <jason@redhat.com>
Date:   Wed Nov 30 14:22:03 2022 -0500

    c++: small contracts fixes
    
    The first is an actual bug: remove_contract_attributes was only keeping one
    attribute.  The second just helps flow analysis in optimizers and static
    analyzers.
    
    gcc/cp/ChangeLog:
    
            * contracts.cc (remove_contract_attributes): Actually prepend
            to the list.
            * pt.cc (tsubst_contract): Only look for a postcondition if type is
            nonnull.

Diff:
---
 gcc/cp/contracts.cc | 2 +-
 gcc/cp/pt.cc        | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/gcc/cp/contracts.cc b/gcc/cp/contracts.cc
index a9097016768..45f52b20392 100644
--- a/gcc/cp/contracts.cc
+++ b/gcc/cp/contracts.cc
@@ -869,7 +869,7 @@ remove_contract_attributes (tree fndecl)
   tree list = NULL_TREE;
   for (tree p = DECL_ATTRIBUTES (fndecl); p; p = TREE_CHAIN (p))
     if (!cxx_contract_attribute_p (p))
-      list = tree_cons (TREE_PURPOSE (p), TREE_VALUE (p), NULL_TREE);
+      list = tree_cons (TREE_PURPOSE (p), TREE_VALUE (p), list);
   DECL_ATTRIBUTES (fndecl) = nreverse (list);
 }
 
diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index 2d8e4fdd4b5..08de273a900 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -11561,7 +11561,7 @@ tsubst_contract (tree decl, tree t, tree args, tsubst_flags_t complain,
   tree r = copy_node (t);
 
   /* Rebuild the result variable.  */
-  if (POSTCONDITION_P (t) && POSTCONDITION_IDENTIFIER (t))
+  if (type && POSTCONDITION_P (t) && POSTCONDITION_IDENTIFIER (t))
     {
       tree oldvar = POSTCONDITION_IDENTIFIER (t);