[gcc r13-5316] c++: TARGET_EXPR_ELIDING_P and std::move [PR107267]

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

https://gcc.gnu.org/g:4cbc71691e47b1ca6b64feb0af678606705d2f92

commit r13-5316-g4cbc71691e47b1ca6b64feb0af678606705d2f92
Author: Jason Merrill <jason@redhat.com>
Date:   Mon Jan 23 17:14:11 2023 -0500

    c++: TARGET_EXPR_ELIDING_P and std::move [PR107267]
    
    With -ffold-simple-inlines, we turn calls to std::move into the static_cast
    equivalent.  In this testcase, this exposes the FindResult temporary to copy
    elision which is not specified by the standard, through an optimization in
    gimplify_modify_expr_rhs.  Since the type is not TREE_ADDRESSABLE, this is
    not detectable by the user, so we just need to soften the assert.
    
            PR c++/107267
    
    gcc/cp/ChangeLog:
    
            * cp-gimplify.cc (cp_gimplify_init_expr): Allow unexpected elision
            of trivial types.
    
    gcc/testsuite/ChangeLog:
    
            * g++.dg/cpp0x/move2.C: New test.

Diff:
---
 gcc/cp/cp-gimplify.cc              |  5 ++++-
 gcc/testsuite/g++.dg/cpp0x/move2.C | 14 ++++++++++++++
 2 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/gcc/cp/cp-gimplify.cc b/gcc/cp/cp-gimplify.cc
index 340b4641046..83ba1285bfd 100644
--- a/gcc/cp/cp-gimplify.cc
+++ b/gcc/cp/cp-gimplify.cc
@@ -250,7 +250,10 @@ cp_gimplify_init_expr (tree *expr_p)
   if (TREE_CODE (from) == TARGET_EXPR)
     if (tree init = TARGET_EXPR_INITIAL (from))
       {
-	gcc_checking_assert (TARGET_EXPR_ELIDING_P (from));
+	/* Make sure that we expected to elide this temporary.  But also allow
+	   gimplify_modify_expr_rhs to elide temporaries of trivial type.  */
+	gcc_checking_assert (TARGET_EXPR_ELIDING_P (from)
+			     || !TREE_ADDRESSABLE (TREE_TYPE (from)));
 	if (target_expr_needs_replace (from))
 	  {
 	    /* If this was changed by cp_genericize_target_expr, we need to
diff --git a/gcc/testsuite/g++.dg/cpp0x/move2.C b/gcc/testsuite/g++.dg/cpp0x/move2.C
new file mode 100644
index 00000000000..b8c8683c4d2
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/move2.C
@@ -0,0 +1,14 @@
+// PR c++/107267
+// { dg-do compile { target c++11 } }
+// { dg-additional-options -ffold-simple-inlines }
+
+namespace std {
+  template<typename _Tp> _Tp &&move(_Tp &&);
+}
+
+struct FindResult {
+  FindResult();
+  int result;
+};
+
+FindResult pop_ret = std::move(FindResult());