c++: Only do maybe_init_list_as_range optimization if !processing_template_decl [PR108047]

The last testcase in this patch ICEs, because
maybe_init_list_as_range -> maybe_init_list_as_array
calls maybe_constant_init in:
  /* Don't do this if the conversion would be constant.  */
  first = maybe_constant_init (first);
  if (TREE_CONSTANT (first))
    return NULL_TREE;
but maybe_constant_init shouldn't be called when processing_template_decl.
While we could replace that call with fold_non_dependent_init, my limited
understanding is that this is an optimization and even if we don't optimize
it when processing_template_decl, build_user_type_conversion_1 will be
called again during instantiation with !processing_template_decl if it is
every instantiated and we can do the optimization only then.

2023-01-09  Jakub Jelinek  <jakub@redhat.com>

	PR c++/105838
	PR c++/108047
	PR c++/108266
	* call.cc (maybe_init_list_as_range): Always return NULL_TREE if
	processing_template_decl.

	* g++.dg/tree-ssa/initlist-opt2.C: New test.
	* g++.dg/tree-ssa/initlist-opt3.C: New test.

3 files changed, 54 insertions, 1 deletions

diff --git a/gcc/cp/call.cc b/gcc/cp/call.cc
index c25df17..bd174b8 100644
--- a/gcc/cp/call.cc
+++ b/gcc/cp/call.cc
@@ -4285,7 +4285,8 @@ maybe_init_list_as_array (tree elttype, tree init)
 static tree
 maybe_init_list_as_range (tree fn, tree expr)
 {
-  if (BRACE_ENCLOSED_INITIALIZER_P (expr)
+  if (!processing_template_decl
+      && BRACE_ENCLOSED_INITIALIZER_P (expr)
       && is_list_ctor (fn)
       && decl_in_std_namespace_p (fn))
     {
diff --git a/gcc/testsuite/g++.dg/tree-ssa/initlist-opt2.C b/gcc/testsuite/g++.dg/tree-ssa/initlist-opt2.C
new file mode 100644
index 0000000..c20713a
--- /dev/null
+++ b/gcc/testsuite/g++.dg/tree-ssa/initlist-opt2.C
@@ -0,0 +1,31 @@
+// PR c++/105838
+// { dg-additional-options -fdump-tree-gimple }
+// { dg-do compile { target c++11 } }
+
+// Test that we do range-initialization from const char *.
+// { dg-final { scan-tree-dump {_M_range_initialize<const char\* const\*>} "gimple" } }
+
+#include <string>
+#include <vector>
+
+void g (const void *);
+
+template <int N>
+void f (const char *p)
+{
+  std::vector<std::string> lst = {
+  "aahing", "aaliis", "aarrgh", "abacas", "abacus", "abakas", "abamps", "abands", "abased", "abaser", "abases", "abasia",
+  "abated", "abater", "abates", "abatis", "abator", "abattu", "abayas", "abbacy", "abbess", "abbeys", "abbots", "abcees",
+  "abdabs", "abduce", "abduct", "abears", "abeigh", "abeles", "abelia", "abends", "abhors", "abided", "abider", "abides",
+  "abject", "abjure", "ablate", "ablaut", "ablaze", "ablest", "ablets", "abling", "ablins", "abloom", "ablush", "abmhos",
+  "aboard", "aboded", "abodes", "abohms", "abolla", "abomas", "aboral", "abords", "aborne", "aborts", "abound", "abouts",
+  "aboves", "abrade", "abraid", "abrash", "abrays", "abrazo", "abrege", "abrins", "abroad", "abrupt", "abseil", "absent",
+  };
+
+  g(&lst);
+}
+
+void h (const char *p)
+{
+  f<0> (p);
+}
diff --git a/gcc/testsuite/g++.dg/tree-ssa/initlist-opt3.C b/gcc/testsuite/g++.dg/tree-ssa/initlist-opt3.C
new file mode 100644
index 0000000..c750b99
--- /dev/null
+++ b/gcc/testsuite/g++.dg/tree-ssa/initlist-opt3.C
@@ -0,0 +1,21 @@
+// PR c++/108266
+// { dg-do compile { target c++11 } }
+
+#include <initializer_list>
+#include <vector>
+
+struct S { S (const char *); };
+void bar (std::vector<S>);
+
+template <int N>
+void
+foo ()
+{
+  bar ({"", ""});
+}
+
+void
+baz ()
+{
+  foo<0> ();
+}