[gcc r13-4565] c++: build initializer_list<string> in a loop [PR105838]

[gcc r13-4565] c++: build initializer_list<string> in a loop [PR105838]

[Jason Merrill]

https://gcc.gnu.org/g:bd0485f20f4794f9787237706a6308473a8e9415

commit r13-4565-gbd0485f20f4794f9787237706a6308473a8e9415
Author: Jason Merrill <jason@redhat.com>
Date:   Tue Dec 6 18:10:48 2022 -0500

    c++: build initializer_list<string> in a loop [PR105838]
    
    The previous patch avoided building an initializer_list<string> at all when
    building a vector<string>, but in situations where that isn't possible, we
    could still build the initializer_list with a loop over a constant array.
    
    This is represented using a VEC_INIT_EXPR, which required adjusting a couple
    of places that expected the initializer array to have the same type as the
    target array and fixing build_vec_init not to undo our efforts.
    
            PR c++/105838
    
    gcc/cp/ChangeLog:
    
            * call.cc (convert_like_internal) [ck_list]: Use
            maybe_init_list_as_array.
            * constexpr.cc (cxx_eval_vec_init_1): Init might have
            a different type.
            * tree.cc (build_vec_init_elt): Likewise.
            * init.cc (build_vec_init): Handle from_array from a
            TARGET_EXPR.  Retain TARGET_EXPR of a different type.
    
    gcc/testsuite/ChangeLog:
    
            * g++.dg/tree-ssa/initlist-opt2.C: New test.

Diff:
---
 gcc/cp/call.cc                                | 11 ++++++++++-
 gcc/cp/constexpr.cc                           |  6 +++---
 gcc/cp/init.cc                                | 13 +++++++++++--
 gcc/cp/tree.cc                                |  2 --
 gcc/testsuite/g++.dg/tree-ssa/initlist-opt2.C | 24 ++++++++++++++++++++++++
 5 files changed, 48 insertions(+), 8 deletions(-)

diff --git a/gcc/cp/call.cc b/gcc/cp/call.cc
index 33b5e7f87f5..14aa96dd328 100644
--- a/gcc/cp/call.cc
+++ b/gcc/cp/call.cc
@@ -8501,7 +8501,16 @@ convert_like_internal (conversion *convs, tree expr, tree fn, int argnum,
 	unsigned len = CONSTRUCTOR_NELTS (expr);
 	tree array;
 
-	if (len)
+	if (tree init = maybe_init_list_as_array (elttype, expr))
+	  {
+	    elttype = cp_build_qualified_type
+	      (elttype, cp_type_quals (elttype) | TYPE_QUAL_CONST);
+	    array = build_array_of_n_type (elttype, len);
+	    array = build_vec_init_expr (array, init, complain);
+	    array = get_target_expr (array);
+	    array = cp_build_addr_expr (array, complain);
+	  }
+	else if (len)
 	  {
 	    tree val; unsigned ix;
 
diff --git a/gcc/cp/constexpr.cc b/gcc/cp/constexpr.cc
index e43d92864f5..3f7892aa88a 100644
--- a/gcc/cp/constexpr.cc
+++ b/gcc/cp/constexpr.cc
@@ -5255,12 +5255,12 @@ cxx_eval_vec_init_1 (const constexpr_ctx *ctx, tree atype, tree init,
       else
 	{
 	  /* Copying an element.  */
-	  gcc_assert (same_type_ignoring_top_level_qualifiers_p
-		      (atype, TREE_TYPE (init)));
 	  eltinit = cp_build_array_ref (input_location, init, idx, complain);
 	  if (!lvalue_p (init))
 	    eltinit = move (eltinit);
-	  eltinit = force_rvalue (eltinit, complain);
+	  eltinit = (perform_implicit_conversion_flags
+		     (elttype, eltinit, complain,
+		      LOOKUP_IMPLICIT|LOOKUP_NO_NARROWING));
 	  eltinit = cxx_eval_constant_expression (&new_ctx, eltinit, lval,
 						  non_constant_p, overflow_p);
 	}
diff --git a/gcc/cp/init.cc b/gcc/cp/init.cc
index 428fac5621c..1ccde7cf8ad 100644
--- a/gcc/cp/init.cc
+++ b/gcc/cp/init.cc
@@ -4420,7 +4420,9 @@ build_vec_init (tree base, tree maxindex, tree init,
   /* Look through the TARGET_EXPR around a compound literal.  */
   if (init && TREE_CODE (init) == TARGET_EXPR
       && TREE_CODE (TARGET_EXPR_INITIAL (init)) == CONSTRUCTOR
-      && from_array != 2)
+      && from_array != 2
+      && (same_type_ignoring_top_level_qualifiers_p
+	  (TREE_TYPE (init), atype)))
     init = TARGET_EXPR_INITIAL (init);
 
   if (tree vi = get_vec_init_expr (init))
@@ -4546,7 +4548,14 @@ build_vec_init (tree base, tree maxindex, tree init,
     {
       if (lvalue_kind (init) & clk_rvalueref)
 	xvalue = true;
-      base2 = decay_conversion (init, complain);
+      if (TREE_CODE (init) == TARGET_EXPR)
+	{
+	  /* Avoid error in decay_conversion.  */
+	  base2 = decay_conversion (TARGET_EXPR_SLOT (init), complain);
+	  base2 = cp_build_compound_expr (init, base2, tf_none);
+	}
+      else
+	base2 = decay_conversion (init, complain);
       if (base2 == error_mark_node)
 	return error_mark_node;
       itype = TREE_TYPE (base2);
diff --git a/gcc/cp/tree.cc b/gcc/cp/tree.cc
index 33bde16f128..a600178239c 100644
--- a/gcc/cp/tree.cc
+++ b/gcc/cp/tree.cc
@@ -785,8 +785,6 @@ build_vec_init_elt (tree type, tree init, tsubst_flags_t complain)
   releasing_vec argvec;
   if (init && !BRACE_ENCLOSED_INITIALIZER_P (init))
     {
-      gcc_assert (same_type_ignoring_top_level_qualifiers_p
-		  (type, TREE_TYPE (init)));
       tree init_type = strip_array_types (TREE_TYPE (init));
       tree dummy = build_dummy_object (init_type);
       if (!lvalue_p (init))
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 00000000000..fc928bb5405
--- /dev/null
+++ b/gcc/testsuite/g++.dg/tree-ssa/initlist-opt2.C
@@ -0,0 +1,24 @@
+// PR c++/105838
+// { dg-additional-options -fdump-tree-gimple }
+// { dg-do compile { target c++11 } }
+
+// Check that we call the basic_string constructor once (and define it once).
+// { dg-final { scan-tree-dump-times {>::basic_string} 2 "gimple" } }
+
+#include <string>
+
+void g (const void *);
+
+void f (const char *p)
+{
+  std::initializer_list<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);
+}