c-family: Add __builtin_assoc_barrier

New builtin to enable explicit use of PAREN_EXPR in C & C++ code.

Signed-off-by: Matthias Kretz <m.kretz@gsi.de>

gcc/testsuite/ChangeLog:

	* c-c++-common/builtin-assoc-barrier-1.c: New test.

gcc/cp/ChangeLog:

	* constexpr.c (cxx_eval_constant_expression): Handle PAREN_EXPR
	via cxx_eval_constant_expression.
	* cp-objcp-common.c (names_builtin_p): Handle
	RID_BUILTIN_ASSOC_BARRIER.
	* cp-tree.h: Adjust TREE_LANG_FLAG documentation to include
	PAREN_EXPR in REF_PARENTHESIZED_P.
	(REF_PARENTHESIZED_P): Add PAREN_EXPR.
	* parser.c (cp_parser_postfix_expression): Handle
	RID_BUILTIN_ASSOC_BARRIER.
	* pt.c (tsubst_copy_and_build): If the PAREN_EXPR is not a
	parenthesized initializer, build a new PAREN_EXPR.
	* semantics.c (force_paren_expr): Simplify conditionals. Set
	REF_PARENTHESIZED_P on PAREN_EXPR.
	(maybe_undo_parenthesized_ref): Test PAREN_EXPR for
	REF_PARENTHESIZED_P.

gcc/c-family/ChangeLog:

	* c-common.c (c_common_reswords): Add __builtin_assoc_barrier.
	* c-common.h (enum rid): Add RID_BUILTIN_ASSOC_BARRIER.

gcc/c/ChangeLog:

	* c-decl.c (names_builtin_p): Handle RID_BUILTIN_ASSOC_BARRIER.
	* c-parser.c (c_parser_postfix_expression): Likewise.

gcc/ChangeLog:

	* doc/extend.texi: Document __builtin_assoc_barrier.

6 files changed, 46 insertions, 22 deletions

diff --git a/gcc/cp/constexpr.c b/gcc/cp/constexpr.c
index 69d9d3d..c8f9d5f 100644
--- a/gcc/cp/constexpr.c
+++ b/gcc/cp/constexpr.c
@@ -6901,6 +6901,14 @@ cxx_eval_constant_expression (const constexpr_ctx *ctx, tree t,
 				       non_constant_p, overflow_p);
       break;
 
+    case PAREN_EXPR:
+      gcc_assert (!REF_PARENTHESIZED_P (t));
+      /* A PAREN_EXPR resulting from __builtin_assoc_barrier has no effect in
+         constant expressions since it's unaffected by -fassociative-math.  */
+      r = cxx_eval_constant_expression (ctx, TREE_OPERAND (t, 0), lval,
+					non_constant_p, overflow_p);
+      break;
+
     case NOP_EXPR:
       if (REINTERPRET_CAST_P (t))
 	{
diff --git a/gcc/cp/cp-objcp-common.c b/gcc/cp/cp-objcp-common.c
index 28f2d7b..38eae88 100644
--- a/gcc/cp/cp-objcp-common.c
+++ b/gcc/cp/cp-objcp-common.c
@@ -404,6 +404,7 @@ names_builtin_p (const char *name)
     case RID_BUILTIN_SHUFFLE:
     case RID_BUILTIN_SHUFFLEVECTOR:
     case RID_BUILTIN_LAUNDER:
+    case RID_BUILTIN_ASSOC_BARRIER:
     case RID_BUILTIN_BIT_CAST:
     case RID_OFFSETOF:
     case RID_HAS_NOTHROW_ASSIGN:
diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h
index acc98c9..3f56cb9 100644
--- a/gcc/cp/cp-tree.h
+++ b/gcc/cp/cp-tree.h
@@ -473,7 +473,8 @@ extern GTY(()) tree cp_global_trees[CPTI_MAX];
       TARGET_EXPR_DIRECT_INIT_P (in TARGET_EXPR)
       FNDECL_USED_AUTO (in FUNCTION_DECL)
       DECLTYPE_FOR_LAMBDA_PROXY (in DECLTYPE_TYPE)
-      REF_PARENTHESIZED_P (in COMPONENT_REF, INDIRECT_REF, SCOPE_REF, VIEW_CONVERT_EXPR)
+      REF_PARENTHESIZED_P (in COMPONENT_REF, INDIRECT_REF, SCOPE_REF,
+			   VIEW_CONVERT_EXPR, PAREN_EXPR)
       AGGR_INIT_ZERO_FIRST (in AGGR_INIT_EXPR)
       CONSTRUCTOR_MUTABLE_POISON (in CONSTRUCTOR)
       OVL_HIDDEN_P (in OVERLOAD)
@@ -4041,12 +4042,13 @@ struct GTY(()) lang_decl {
 #define PAREN_STRING_LITERAL_P(NODE) \
   TREE_LANG_FLAG_0 (STRING_CST_CHECK (NODE))
 
-/* Indicates whether a COMPONENT_REF or a SCOPE_REF has been parenthesized, or
-   an INDIRECT_REF comes from parenthesizing a _DECL.  Currently only set some
-   of the time in C++14 mode.  */
+/* Indicates whether a COMPONENT_REF or a SCOPE_REF has been parenthesized, an
+   INDIRECT_REF comes from parenthesizing a _DECL, or a PAREN_EXPR identifies a
+   parenthesized initializer relevant for decltype(auto).  Currently only set
+   some of the time in C++14 mode.  */
 
 #define REF_PARENTHESIZED_P(NODE) \
-  TREE_LANG_FLAG_2 (TREE_CHECK4 ((NODE), COMPONENT_REF, INDIRECT_REF, SCOPE_REF, VIEW_CONVERT_EXPR))
+  TREE_LANG_FLAG_2 (TREE_CHECK5 ((NODE), COMPONENT_REF, INDIRECT_REF, SCOPE_REF, VIEW_CONVERT_EXPR, PAREN_EXPR))
 
 /* Nonzero if this AGGR_INIT_EXPR provides for initialization via a
    constructor call, rather than an ordinary function call.  */
diff --git a/gcc/cp/parser.c b/gcc/cp/parser.c
index 154b40e..65f0f11 100644
--- a/gcc/cp/parser.c
+++ b/gcc/cp/parser.c
@@ -7354,6 +7354,7 @@ cp_parser_postfix_expression (cp_parser *parser, bool address_p, bool cast_p,
     case RID_BUILTIN_SHUFFLE:
     case RID_BUILTIN_SHUFFLEVECTOR:
     case RID_BUILTIN_LAUNDER:
+    case RID_BUILTIN_ASSOC_BARRIER:
       {
 	vec<tree, va_gc> *vec;
 
@@ -7396,6 +7397,19 @@ cp_parser_postfix_expression (cp_parser *parser, bool address_p, bool cast_p,
 	      }
 	    break;
 
+	  case RID_BUILTIN_ASSOC_BARRIER:
+	    if (vec->length () == 1)
+	      postfix_expression = build1_loc (loc, PAREN_EXPR,
+					       TREE_TYPE ((*vec)[0]),
+					       (*vec)[0]);
+	    else
+	      {
+		error_at (loc, "wrong number of arguments to "
+			       "%<__builtin_assoc_barrier%>");
+		postfix_expression = error_mark_node;
+	      }
+	    break;
+
 	  case RID_BUILTIN_SHUFFLE:
 	    if (vec->length () == 2)
 	      postfix_expression
diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index 82bf7dc..b27eea3 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -21010,7 +21010,15 @@ tsubst_copy_and_build (tree t,
 	     integral_constant_expression_p));
 
     case PAREN_EXPR:
-      RETURN (finish_parenthesized_expr (RECUR (TREE_OPERAND (t, 0))));
+      if (REF_PARENTHESIZED_P (t))
+	RETURN (finish_parenthesized_expr (RECUR (TREE_OPERAND (t, 0))));
+      else
+	/* Recreate the PAREN_EXPR from __builtin_assoc_barrier.  */
+	{
+	  tree op0 = RECUR (TREE_OPERAND (t, 0));
+	  RETURN (build1_loc (input_location, PAREN_EXPR,
+			      TREE_TYPE (op0), op0));
+	}
 
     case VEC_PERM_EXPR:
       {
diff --git a/gcc/cp/semantics.c b/gcc/cp/semantics.c
index 1540442..8f79f04 100644
--- a/gcc/cp/semantics.c
+++ b/gcc/cp/semantics.c
@@ -2048,24 +2048,17 @@ force_paren_expr (tree expr, bool even_uneval)
   if (cp_unevaluated_operand && !even_uneval)
     return expr;
 
-  if (!DECL_P (tree_strip_any_location_wrapper (expr))
-      && TREE_CODE (expr) != COMPONENT_REF
-      && TREE_CODE (expr) != SCOPE_REF)
-    return expr;
-
-  location_t loc = cp_expr_location (expr);
-
   if (TREE_CODE (expr) == COMPONENT_REF
       || TREE_CODE (expr) == SCOPE_REF)
     REF_PARENTHESIZED_P (expr) = true;
-  else if (processing_template_decl)
-    expr = build1_loc (loc, PAREN_EXPR, TREE_TYPE (expr), expr);
-  else
+  else if (DECL_P (tree_strip_any_location_wrapper (expr)))
     {
-      expr = build1_loc (loc, VIEW_CONVERT_EXPR, TREE_TYPE (expr), expr);
+      location_t loc = cp_expr_location (expr);
+      const tree_code code = processing_template_decl ? PAREN_EXPR
+						      : VIEW_CONVERT_EXPR;
+      expr = build1_loc (loc, code, TREE_TYPE (expr), expr);
       REF_PARENTHESIZED_P (expr) = true;
     }
-
   return expr;
 }
 
@@ -2090,10 +2083,8 @@ maybe_undo_parenthesized_ref (tree t)
 		  || TREE_CODE (t) == STATIC_CAST_EXPR);
       t = TREE_OPERAND (t, 0);
     }
-  else if (TREE_CODE (t) == PAREN_EXPR)
-    t = TREE_OPERAND (t, 0);
-  else if (TREE_CODE (t) == VIEW_CONVERT_EXPR
-	   && REF_PARENTHESIZED_P (t))
+  else if ((TREE_CODE (t) == PAREN_EXPR || TREE_CODE (t) == VIEW_CONVERT_EXPR)
+	     && REF_PARENTHESIZED_P (t))
     t = TREE_OPERAND (t, 0);
 
   return t;