[PATCH] c++: Fix up assert in build_vec_init [PR126752]

Hi!

The following testcase ICEs in an assert added by Marek in
r15-6308.  A subsequent change r15-6897 made the code added in
the former commit no longer trigger on anything in the testsuite,
including the initlist-array{23,24}.C tests added for it.
Later on I've added an optimization in r16-343 so that cleanups
clear rval instead of setting iterator to maxindex but missed
this spot and nothing in the testsuite triggered it.

The following patch adjusts the assert to what the r16-343 change
does.

Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk/16.3?

2026-08-17  Jakub Jelinek  <[email protected]>

	PR c++/126752
	* init.cc (build_vec_init): Assert TREE_PURPOSE of the
	last *cleanup_flags element is rval rather than iterator.

	* g++.dg/cpp0x/initlist-array25.C: New test.

--- gcc/cp/init.cc.jj	2026-06-25 10:03:50.807436517 +0200
+++ gcc/cp/init.cc	2026-08-17 11:46:04.686289531 +0200
@@ -5365,7 +5365,7 @@ build_vec_init (tree base, tree maxindex
 	      && !vec_safe_is_empty (*cleanup_flags))
 	    {
 	      auto l = (*cleanup_flags)->last ();
-	      gcc_assert (TREE_PURPOSE (l) == iterator);
+	      gcc_assert (TREE_PURPOSE (l) == rval);
 	      (*cleanup_flags)->pop ();
 	    }
 	  tree const_init = build_constructor (atype, const_vec);
--- gcc/testsuite/g++.dg/cpp0x/initlist-array25.C.jj	2026-08-17 11:43:57.918910197 +0200
+++ gcc/testsuite/g++.dg/cpp0x/initlist-array25.C	2026-08-17 11:43:23.403351461 +0200
@@ -0,0 +1,12 @@
+// PR c++/126752
+// { dg-do compile { target c++11 } }
+
+struct A {
+  struct B { constexpr B () {} };
+  struct C { ~C (); B c; };
+  struct D : private C {};
+  struct E { E (); };
+  struct F { D f {}; };
+  struct G { F g[1] {}; E h; };
+  void foo () { G {}; }
+};

	Jakub