[gcc r12-5286] c++: split_nonconstant_init and flexarrays

[gcc r12-5286] c++: split_nonconstant_init and flexarrays

[Jason Merrill]

https://gcc.gnu.org/g:29e4163a092ce08ba3a88a05ac2fa3f23b1cec28

commit r12-5286-g29e4163a092ce08ba3a88a05ac2fa3f23b1cec28
Author: Jason Merrill <jason@redhat.com>
Date:   Mon Nov 15 12:59:08 2021 -0500

    c++: split_nonconstant_init and flexarrays
    
    split_nonconstant_init was doing the wrong thing for both the initialization
    and cleanup here; we know the size from the initializer, and we can pass it
    along.  This doesn't make the testcase work, since the y destructor is still
    broken, but it removes the wrong error for the aggregate initialization.
    
    gcc/cp/ChangeLog:
    
            * typeck2.c (split_nonconstant_init_1): Handle flexarrays better.
    
    gcc/testsuite/ChangeLog:
    
            * g++.dg/ext/flexary37.C: Remove expected error.

Diff:
---
 gcc/cp/typeck2.c                     | 9 +++++++++
 gcc/testsuite/g++.dg/ext/flexary37.C | 2 +-
 2 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/gcc/cp/typeck2.c b/gcc/cp/typeck2.c
index c01f2f8ced4..e98fbf7f5fa 100644
--- a/gcc/cp/typeck2.c
+++ b/gcc/cp/typeck2.c
@@ -484,6 +484,15 @@ split_nonconstant_init_1 (tree dest, tree init, bool nested)
 	   && TYPE_HAS_NONTRIVIAL_DESTRUCTOR (type))
 	  || vla_type_p (type))
 	{
+	  if (!TYPE_DOMAIN (type)
+	      && TREE_CODE (init) == CONSTRUCTOR
+	      && CONSTRUCTOR_NELTS (init))
+	    {
+	      /* Flexible array.  */
+	      cp_complete_array_type (&type, init, /*default*/true);
+	      dest = build1 (VIEW_CONVERT_EXPR, type, dest);
+	    }
+
 	  /* For an array, we only need/want a single cleanup region rather
 	     than one per element.  */
 	  tree code = build_vec_init (dest, NULL_TREE, init, false, 1,
diff --git a/gcc/testsuite/g++.dg/ext/flexary37.C b/gcc/testsuite/g++.dg/ext/flexary37.C
index ceb5053de2e..5cd48c1f773 100644
--- a/gcc/testsuite/g++.dg/ext/flexary37.C
+++ b/gcc/testsuite/g++.dg/ext/flexary37.C
@@ -12,4 +12,4 @@ public:
 
 struct y { // { dg-error "unknown array size in delete" }
     int a; C b[];
-} y = { 1, { { 2, 3 } } }; // { dg-error "unknown array size in delete" }
+} y = { 1, { { 2, 3 } } };