From: Jason Merrill <jason@redhat.com>
Date: Tue, 6 Jun 2023 03:58:32 +0000 (-0400)
Subject: c++: fix contracts with NRV
X-Git-Tag: releases/gcc-12.4.0~577
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=11afe64fb71c83cef7d56fe6c411fb7adeee59cb;p=thirdparty%2Fgcc.git

c++: fix contracts with NRV

The NRV implementation was blindly replacing the operand of RETURN_EXPR,
clobbering anything that check_return_expr might have added on to the actual
initialization, such as checking the postcondition.

GCC 12 note: There are no contracts in GCC 12, but this issue also broke
setting current_retval_sentinel.

gcc/cp/ChangeLog:

	* semantics.cc (finalize_nrv_r): [RETURN_EXPR]: Only replace the
	INIT_EXPR.
---

diff --git a/gcc/cp/semantics.cc b/gcc/cp/semantics.cc
index 5289131e591e..d6351d2d8a32 100644
--- a/gcc/cp/semantics.cc
+++ b/gcc/cp/semantics.cc
@@ -4859,9 +4859,17 @@ finalize_nrv_r (tree* tp, int* walk_subtrees, void* data)
     *walk_subtrees = 0;
   /* Change all returns to just refer to the RESULT_DECL; this is a nop,
      but differs from using NULL_TREE in that it indicates that we care
-     about the value of the RESULT_DECL.  */
+     about the value of the RESULT_DECL.  But preserve anything appended
+     by check_return_expr.  */
   else if (TREE_CODE (*tp) == RETURN_EXPR)
-    TREE_OPERAND (*tp, 0) = dp->result;
+    {
+      tree *p = &TREE_OPERAND (*tp, 0);
+      while (TREE_CODE (*p) == COMPOUND_EXPR)
+	p = &TREE_OPERAND (*p, 0);
+      gcc_checking_assert (TREE_CODE (*p) == INIT_EXPR
+			   && TREE_OPERAND (*p, 0) == dp->result);
+      *p = dp->result;
+    }
   /* Change all cleanups for the NRV to only run when an exception is
      thrown.  */
   else if (TREE_CODE (*tp) == CLEANUP_STMT