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Re: [C++ PATCH] Fix up __builtin_is_constant_evaluated handling in array type sizes (PR c++/88446, take 2)


On Tue, Dec 11, 2018 at 06:02:12PM -0500, Jason Merrill wrote:
> On 12/11/18 4:38 PM, Jakub Jelinek wrote:
> > On Tue, Dec 11, 2018 at 03:35:39PM -0500, Marek Polacek wrote:
> > > >   tree
> > > > -maybe_constant_value (tree t, tree decl)
> > > > +maybe_constant_value (tree t, tree decl, bool pretend_const_required)
> > > >   {
> > > >     tree r;
> > > 
> > > Could you please describe the new param in the comment?
> > > 
> > > Perhaps use /*pretend_const_required=*/true?
> > 
> > Thanks, changed both, plus I've changed the other function's descriptions
> > of that argument from the P0595R1 term (required to be const-evaluated)
> > to the P0595R2 term (manifestly const-evaluated).
> > 
> > Ok for trunk?  Or should I also change pretend_const_required argument
> > name to manifestly_const_eval or something similar?
> 
> I think so, yes.  OK with that change.

Here is what I've committed after committing the other two patches.
Thanks for the review.

2018-12-12  Jakub Jelinek  <jakub@redhat.com>

	PR c++/88446
	* cp-tree.h (maybe_constant_value): Add manifestly_const_eval
	argument.
	* constexpr.c (struct constexpr_call): Rename pretend_const_required
	member to manifestly_const_eval.
	(struct constexpr_ctx): Likewise.
	(constexpr_call_hasher::equal): Adjust users.
	(cxx_eval_builtin_function_call): Likewise.  Formatting fix.
	(cxx_eval_call_expression): Adjust users.
	(cxx_eval_outermost_constant_expr, maybe_constant_init_1,
	maybe_constant_init): Rename pretend_const_required argument to
	manifestly_const_eval, adjust function comments.
	(maybe_constant_value): Add manifestly_const_eval argument.  If true,
	don't cache and call cxx_eval_outermost_constant_expr with true as
	manifestly_const_eval.
	* decl.c (compute_array_index_type_loc): Call maybe_constant_value
	with true as manifestly_const_eval.

	* g++.dg/cpp2a/is-constant-evaluated3.C: New test.

--- gcc/cp/cp-tree.h.jj	2018-12-12 09:22:36.123193623 +0100
+++ gcc/cp/cp-tree.h	2018-12-12 09:32:27.408535853 +0100
@@ -7663,7 +7663,7 @@ extern bool require_rvalue_constant_expr
 extern bool require_potential_rvalue_constant_expression (tree);
 extern tree cxx_constant_value			(tree, tree = NULL_TREE);
 extern tree cxx_constant_init			(tree, tree = NULL_TREE);
-extern tree maybe_constant_value		(tree, tree = NULL_TREE);
+extern tree maybe_constant_value		(tree, tree = NULL_TREE, bool = false);
 extern tree maybe_constant_init			(tree, tree = NULL_TREE, bool = false);
 extern tree fold_non_dependent_expr		(tree, tsubst_flags_t = tf_warning_or_error);
 extern tree fold_simple				(tree);
--- gcc/cp/constexpr.c.jj	2018-12-12 09:27:43.352175869 +0100
+++ gcc/cp/constexpr.c	2018-12-12 09:34:17.531736075 +0100
@@ -977,7 +977,7 @@ struct GTY((for_user)) constexpr_call {
      recalculate it when expanding the hash table.  */
   hashval_t hash;
   /* Whether __builtin_is_constant_evaluated() should evaluate to true.  */
-  bool pretend_const_required;
+  bool manifestly_const_eval;
 };
 
 struct constexpr_call_hasher : ggc_ptr_hash<constexpr_call>
@@ -1025,7 +1025,7 @@ struct constexpr_ctx {
      trying harder to get a constant value.  */
   bool strict;
   /* Whether __builtin_is_constant_evaluated () should be true.  */
-  bool pretend_const_required;
+  bool manifestly_const_eval;
 };
 
 /* A table of all constexpr calls that have been evaluated by the
@@ -1057,7 +1057,7 @@ constexpr_call_hasher::equal (constexpr_
     return true;
   if (lhs->hash != rhs->hash)
     return false;
-  if (lhs->pretend_const_required != rhs->pretend_const_required)
+  if (lhs->manifestly_const_eval != rhs->manifestly_const_eval)
     return false;
   if (!constexpr_fundef_hasher::equal (lhs->fundef, rhs->fundef))
     return false;
@@ -1206,11 +1206,11 @@ cxx_eval_builtin_function_call (const co
     }
 
   /* For __builtin_is_constant_evaluated, defer it if not
-     ctx->pretend_const_required, otherwise fold it to true.  */
+     ctx->manifestly_const_eval, otherwise fold it to true.  */
   if (fndecl_built_in_p (fun, CP_BUILT_IN_IS_CONSTANT_EVALUATED,
-		       BUILT_IN_FRONTEND))
+			 BUILT_IN_FRONTEND))
     {
-      if (!ctx->pretend_const_required)
+      if (!ctx->manifestly_const_eval)
 	{
 	  *non_constant_p = true;
 	  return t;
@@ -1508,7 +1508,7 @@ cxx_eval_call_expression (const constexp
   location_t loc = cp_expr_loc_or_loc (t, input_location);
   tree fun = get_function_named_in_call (t);
   constexpr_call new_call
-    = { NULL, NULL, NULL, 0, ctx->pretend_const_required };
+    = { NULL, NULL, NULL, 0, ctx->manifestly_const_eval };
   bool depth_ok;
 
   if (fun == NULL_TREE)
@@ -1684,7 +1684,7 @@ cxx_eval_call_expression (const constexp
       new_call.hash
 	= iterative_hash_template_arg (new_call.bindings, new_call.hash);
       new_call.hash
-	= iterative_hash_object (ctx->pretend_const_required, new_call.hash);
+	= iterative_hash_object (ctx->manifestly_const_eval, new_call.hash);
 
       /* If we have seen this call before, we are done.  */
       maybe_initialize_constexpr_call_table ();
@@ -5022,13 +5022,13 @@ instantiate_constexpr_fns (tree t)
    STRICT has the same sense as for constant_value_1: true if we only allow
    conforming C++ constant expressions, or false if we want a constant value
    even if it doesn't conform.
-   PRETEND_CONST_REQUIRED is true if T is required to be const-evaluated as
+   MANIFESTLY_CONST_EVAL is true if T is manifestly const-evaluated as
    per P0595 even when ALLOW_NON_CONSTANT is true.  */
 
 static tree
 cxx_eval_outermost_constant_expr (tree t, bool allow_non_constant,
 				  bool strict = true,
-				  bool pretend_const_required = false,
+				  bool manifestly_const_eval = false,
 				  tree object = NULL_TREE)
 {
   auto_timevar time (TV_CONSTEXPR);
@@ -5039,7 +5039,7 @@ cxx_eval_outermost_constant_expr (tree t
 
   constexpr_ctx ctx = { NULL, &map, NULL, NULL, NULL, NULL,
 			allow_non_constant, strict,
-			pretend_const_required || !allow_non_constant };
+			manifestly_const_eval || !allow_non_constant };
 
   tree type = initialized_type (t);
   tree r = t;
@@ -5131,7 +5131,7 @@ cxx_eval_outermost_constant_expr (tree t
       /* If __builtin_is_constant_evaluated () was evaluated to true
 	 and the result is not a valid constant expression, we need to
 	 punt.  */
-      if (pretend_const_required)
+      if (manifestly_const_eval)
 	return cxx_eval_outermost_constant_expr (t, true, strict,
 						 false, object);
       /* This isn't actually constant, so unset TREE_CONSTANT.
@@ -5274,12 +5274,14 @@ fold_simple (tree t)
 
 /* If T is a constant expression, returns its reduced value.
    Otherwise, if T does not have TREE_CONSTANT set, returns T.
-   Otherwise, returns a version of T without TREE_CONSTANT.  */
+   Otherwise, returns a version of T without TREE_CONSTANT.
+   MANIFESTLY_CONST_EVAL is true if T is manifestly const-evaluated
+   as per P0595.  */
 
 static GTY((deletable)) hash_map<tree, tree> *cv_cache;
 
 tree
-maybe_constant_value (tree t, tree decl)
+maybe_constant_value (tree t, tree decl, bool manifestly_const_eval)
 {
   tree r;
 
@@ -5296,6 +5298,9 @@ maybe_constant_value (tree t, tree decl)
     /* No caching or evaluation needed.  */
     return t;
 
+  if (manifestly_const_eval)
+    return cxx_eval_outermost_constant_expr (t, true, true, true, decl);
+
   if (cv_cache == NULL)
     cv_cache = hash_map<tree, tree>::create_ggc (101);
   if (tree *cached = cv_cache->get (t))
@@ -5399,12 +5404,12 @@ fold_non_dependent_expr (tree t,
 /* Like maybe_constant_value, but returns a CONSTRUCTOR directly, rather
    than wrapped in a TARGET_EXPR.
    ALLOW_NON_CONSTANT is false if T is required to be a constant expression.
-   PRETEND_CONST_REQUIRED is true if T is required to be const-evaluated as
+   MANIFESTLY_CONST_EVAL is true if T is manifestly const-evaluated as
    per P0595 even when ALLOW_NON_CONSTANT is true.  */
 
 static tree
 maybe_constant_init_1 (tree t, tree decl, bool allow_non_constant,
-		       bool pretend_const_required)
+		       bool manifestly_const_eval)
 {
   if (!t)
     return t;
@@ -5424,7 +5429,7 @@ maybe_constant_init_1 (tree t, tree decl
   else
     t = cxx_eval_outermost_constant_expr (t, allow_non_constant,
 					  /*strict*/false,
-					  pretend_const_required, decl);
+					  manifestly_const_eval, decl);
   if (TREE_CODE (t) == TARGET_EXPR)
     {
       tree init = TARGET_EXPR_INITIAL (t);
@@ -5437,9 +5442,9 @@ maybe_constant_init_1 (tree t, tree decl
 /* Wrapper for maybe_constant_init_1 which permits non constants.  */
 
 tree
-maybe_constant_init (tree t, tree decl, bool pretend_const_required)
+maybe_constant_init (tree t, tree decl, bool manifestly_const_eval)
 {
-  return maybe_constant_init_1 (t, decl, true, pretend_const_required);
+  return maybe_constant_init_1 (t, decl, true, manifestly_const_eval);
 }
 
 /* Wrapper for maybe_constant_init_1 which does not permit non constants.  */
--- gcc/cp/decl.c.jj	2018-12-12 09:22:36.123193623 +0100
+++ gcc/cp/decl.c	2018-12-12 09:33:10.889825223 +0100
@@ -9646,7 +9646,11 @@ compute_array_index_type_loc (location_t
 	{
 	  size = instantiate_non_dependent_expr_sfinae (size, complain);
 	  size = build_converted_constant_expr (size_type_node, size, complain);
-	  size = maybe_constant_value (size);
+	  /* Pedantically a constant expression is required here and so
+	     __builtin_is_constant_evaluated () should fold to true if it
+	     is successfully folded into a constant.  */
+	  size = maybe_constant_value (size, NULL_TREE,
+				       /*manifestly_const_eval=*/true);
 
 	  if (!TREE_CONSTANT (size))
 	    size = osize;
--- gcc/testsuite/g++.dg/cpp2a/is-constant-evaluated3.C.jj	2018-12-12 09:32:27.415535739 +0100
+++ gcc/testsuite/g++.dg/cpp2a/is-constant-evaluated3.C	2018-12-12 09:32:27.415535739 +0100
@@ -0,0 +1,26 @@
+// P0595R1
+// { dg-do run { target c++14 } }
+
+struct false_type { static constexpr bool value = false; };
+struct true_type { static constexpr bool value = true; };
+template<class T, class U>
+struct is_same : false_type {};
+template<class T>
+struct is_same<T, T> : true_type {};
+
+int a[__builtin_is_constant_evaluated () ? 1 : 2];
+int b[1];
+static_assert (is_same<decltype (a), decltype (b)>::value, "");
+
+int
+main ()
+{
+  int c[__builtin_is_constant_evaluated () ? 3 : 4];
+  int d[3];
+  static_assert (is_same<decltype (c), decltype (d)>::value, "");
+  int (*e)[7][9] = new int[__builtin_is_constant_evaluated () ? -1 : 5]
+			  [__builtin_is_constant_evaluated () ? 7 : 8]
+			  [__builtin_is_constant_evaluated () ? 9 : 10];
+  e[0][0][0] = 6;
+  delete[] e;
+}


	Jakub


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