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C++ PATCH for P1152R4: Deprecating some uses of volatile (PR c++/91361)


This patch implements another C++20 feature, partially deprecating volatile.
You can read the proposal here: <http://wg21.link/p1152r4>.  I encourage
interested people to read the background in <http://wg21.link/p1152r0> which
provides a lot of interesting volatile-related information.

Note that P1152R4 differs slightly from what's now in the standard: the mention
of "non-class type" was dropped.  (Assignment to objects of a class type is
defined by the copy/move assignment operator.)

The gist is that expressions that involve both load and store of a volatile
lvalue, such as ++ or += are deprecated, as are volatile-qualified parameter
and return types.  Chained assignments of the form "a = b = c" are also
deprecated because there's some confusion as to if 'b' is re-read before storing
the value to 'a' (GCC claims not to do it).  See Annex D [depr.volatile.type].

[expr.ass] further says that "A simple assignment whose left operand is of
a volatile-qualified type is deprecated unless the assignment is either
a discarded-value expression or appears in an unevaluated context."
and therein lies the rub.  When parsing/building the MODIFY_EXPR, we don't know
if the assignment's value is going to be discared.  We only know that after
mark_discarded_use has run, which for expression-statements takes place in
finish_expr_stmt -> conver_to_void, and that is quite late.  After much poking
I figured I could set the TREE_THIS_VOLATILE flag in a MODIFY_EXPR, maybe let
mark_discarded_use clear it, and give the warning in cp_genericize_r if it sees
a MODIFY_EXPR marked as TREE_THIS_VOLATILE, which seems to work swimmingly, but
we must ensure that we don't drop that flag along the way.  And some obligatory
location improvements.

Relatedly, <https://gcc.gnu.org/onlinedocs/gcc/C_002b_002b-Volatiles.html>
seems to be out of date after DR 1054; the doc says "The C++ standard specifies
that such expressions do not undergo lvalue to rvalue conversion" but according
to [expr.context] the lvalue-to-rvalue conversion is applied if and only if the
expression is a glvalue of volatile-qualified type and it is one of the following:
[...]
-- indirection,
though I haven't checked if we really do the lvalue-to-rvalue conversion now.

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

2019-08-23  Marek Polacek  <polacek@redhat.com>

	Implement P1152R4: Deprecating some uses of volatile.
	PR c++/91361
	* c-opts.c (c_common_post_options): Enable -Wvolatile by
	default for C++2a, unless -Wno-deprecated.
	* c.opt (Wvolatile): New warning.

	* cp-gimplify.c (cp_genericize_r): Emit a -Wvolatile warning if
	a MODIFY_EXPR is TREE_THIS_VOLATILE.
	(cp_fold): Set TREE_THIS_VOLATILE.
	* decl.c (grokdeclarator): Warn about a volatile-qualified structured
	binding and return type.
	(grokparms): Warn about a volatile-qualified function parameter.
	* expr.c (mark_discarded_use): Clear TREE_THIS_VOLATILE in a
	MODIFY_EXPR if it's a discarded-value expression.
	* typeck.c (cp_build_unary_op): Emit a -Wvolatile warning for pre and
	post ++/-- on a volatile operand.
	(genericize_compound_lvalue): Use a better location.  Don't lose
	TREE_THIS_VOLATILE.
	(cp_build_modify_expr): Emit a -Wvolatile warning for a compound
	assignment whose LHS is volatile-qualified.  Set TREE_THIS_VOLATILE
	in a simple assignment when the LHS is volatile-qualified.  Build
	the assignment with a more precise location.

	* doc/invoke.texi: Document -Wvolatile.

	* c-c++-common/Wbool-operation-1.c: Use -Wno-volatile in C++.
	* c-c++-common/gomp/atomic-1.c: Likewise.
	* c-c++-common/gomp/atomic-9.c: Likewise.
	* c-c++-common/gomp/depend-iterator-1.c: Likewise.
	* c-c++-common/gomp/loop-1.c: Adjust warning location for C++.
	* c-c++-common/gomp/order-3.c: Likewise.
	* c-c++-common/pr69733.c: Use -Wno-volatile in C++.
	* c-c++-common/spec-barrier-2.c: Likewise.
	* c-c++-common/tm/pr54893.c: Likewise.
	* g++.dg/cpp0x/pr65327.C: Add dg-warning.
	* g++.dg/cpp0x/rv-conv2.C: Likewise.
	* g++.dg/cpp0x/rv1n.C: Likewise.
	* g++.dg/cpp0x/rv1p.C: Likewise.
	* g++.dg/cpp0x/rv2n.C: Likewise.
	* g++.dg/cpp0x/rv2p.C: Likewise.
	* g++.dg/cpp0x/rv3n.C: Likewise.
	* g++.dg/cpp0x/rv3p.C: Likewise.
	* g++.dg/cpp0x/rv4n.C: Likewise.
	* g++.dg/cpp0x/rv4p.C: Likewise.
	* g++.dg/cpp0x/rv5n.C: Likewise.
	* g++.dg/cpp0x/rv5p.C: Likewise.
	* g++.dg/cpp0x/rv6n.C: Likewise.
	* g++.dg/cpp0x/rv6p.C: Likewise.
	* g++.dg/cpp0x/rv7n.C: Likewise.
	* g++.dg/cpp0x/rv7p.C: Likewise.
	* g++.dg/cpp0x/rv8p.C: Likewise.
	* g++.dg/cpp0x/trailing14.C: Use -Wno-volatile.
	* g++.dg/cpp1y/new1.C: Add dg-warning.
	* g++.dg/cpp2a/volatile1.C: New test.
	* g++.dg/cpp2a/volatile2.C: New test.
	* g++.dg/cpp2a/volatile3.C: New test.
	* g++.dg/cpp2a/volatile4.C: New test.
	* g++.dg/expr/bool3.C: Add dg-warning.
	* g++.dg/expr/bool4.C: Likewise.
	* g++.dg/expr/cond9.C: Likewise.
	* g++.dg/ext/vector25.C: Likewise.
	* g++.dg/gomp/depend-iterator-1.C: Use -Wno-volatile.
	* g++.dg/inherit/covariant21.C: Add dg-warning.
	* g++.dg/init/ref18.C: Likewise.
	* g++.dg/ipa/pr63838.C: Likewise.
	* g++.dg/overload/rvalue2.C: Likewise.
	* g++.dg/parse/semicolon4.C: Likewise.
	* g++.dg/warn/Wreturn-type-4.C: Likewise.
	* g++.dg/warn/pr36069.C: Likewise.
	* g++.old-deja/g++.mike/p9506.C: Likewise.
	* g++.old-deja/g++.other/volatile1.C: Likewise.

diff --git gcc/c-family/c-opts.c gcc/c-family/c-opts.c
index da783e4990c..fa8cd0ccb09 100644
--- gcc/c-family/c-opts.c
+++ gcc/c-family/c-opts.c
@@ -919,6 +919,10 @@ c_common_post_options (const char **pfilename)
   if (!global_options_set.x_warn_comma_subscript)
     warn_comma_subscript = (cxx_dialect >= cxx2a && warn_deprecated);
 
+  /* -Wvolatile is enabled by default in C++20.  */
+  if (!global_options_set.x_warn_volatile)
+    warn_volatile = (cxx_dialect >= cxx2a && warn_deprecated);
+
   /* Declone C++ 'structors if -Os.  */
   if (flag_declone_ctor_dtor == -1)
     flag_declone_ctor_dtor = optimize_size;
diff --git gcc/c-family/c.opt gcc/c-family/c.opt
index 257cadfa5f1..5adb3c1bcd5 100644
--- gcc/c-family/c.opt
+++ gcc/c-family/c.opt
@@ -1221,6 +1221,10 @@ Wno-vla-larger-than
 C ObjC C++ LTO ObjC++ Alias(Wvla-larger-than=,18446744073709551615EiB,none) Warning
 -Wno-vla-larger-than Disable Wvla-larger-than= warning.  Equivalent to Wvla-larger-than=<SIZE_MAX> or larger.
 
+Wvolatile
+C++ ObjC++ Var(warn_volatile) Warning
+Warn about certain uses of volatile qualifier.
+
 Wvolatile-register-var
 C ObjC C++ ObjC++ Var(warn_volatile_register_var) Warning LangEnabledBy(C ObjC C++ ObjC++,Wall)
 Warn when a register variable is declared volatile.
diff --git gcc/cp/cp-gimplify.c gcc/cp/cp-gimplify.c
index 065dcb7ba06..03ae6b0e92b 100644
--- gcc/cp/cp-gimplify.c
+++ gcc/cp/cp-gimplify.c
@@ -1632,6 +1632,13 @@ cp_genericize_r (tree *stmt_p, int *walk_subtrees, void *data)
 	TARGET_EXPR_NO_ELIDE (stmt) = 1;
       break;
 
+    case MODIFY_EXPR:
+      if (TREE_THIS_VOLATILE (stmt))
+	warning_at (location_of (stmt), OPT_Wvolatile,
+		    "assignment with %<volatile%>-qualified left operand "
+		    "is deprecated");
+      break;
+
     default:
       if (IS_TYPE_OR_DECL_P (stmt))
 	*walk_subtrees = 0;
@@ -2507,6 +2514,9 @@ cp_fold (tree x)
 	  else
 	    x = org_x;
 	}
+      if (code == MODIFY_EXPR && TREE_CODE (x) == MODIFY_EXPR)
+	TREE_THIS_VOLATILE (x) = TREE_THIS_VOLATILE (org_x);
+
       break;
 
     case VEC_COND_EXPR:
diff --git gcc/cp/decl.c gcc/cp/decl.c
index 88aa69ce5de..8da2f3abf83 100644
--- gcc/cp/decl.c
+++ gcc/cp/decl.c
@@ -11188,6 +11188,10 @@ grokdeclarator (const cp_declarator *declarator,
       if (concept_p)
 	error_at (declspecs->locations[ds_concept],
 		  "structured binding declaration cannot be %qs", "concept");
+      /* [dcl.struct.bind] "A cv that includes volatile is deprecated."  */
+      if (type_quals & TYPE_QUAL_VOLATILE)
+	warning_at (declspecs->locations[ds_volatile], OPT_Wvolatile,
+		    "%<volatile%>-qualified structured binding is deprecated");
       switch (storage_class)
 	{
 	case sc_none:
@@ -11576,6 +11580,13 @@ grokdeclarator (const cp_declarator *declarator,
 		if (SCALAR_TYPE_P (type) || VOID_TYPE_P (type))
 		  warning_at (typespec_loc, OPT_Wignored_qualifiers, "type "
 			      "qualifiers ignored on function return type");
+		/* [dcl.fct] "A volatile-qualified return type is
+		   deprecated."  */
+		if (type_quals & TYPE_QUAL_VOLATILE)
+		  warning_at (typespec_loc, OPT_Wvolatile,
+			      "%<volatile%>-qualified return type is "
+			      "deprecated");
+
 		/* We now know that the TYPE_QUALS don't apply to the
 		   decl, but to its return type.  */
 		type_quals = TYPE_UNQUALIFIED;
@@ -13314,6 +13325,13 @@ grokparms (tree parmlist, tree *parms)
 		cp_warn_deprecated_use (deptype);
 	    }
 
+	  /* [dcl.fct] "A parameter with volatile-qualified type is
+	     deprecated."  */
+	  if (CP_TYPE_VOLATILE_P (type))
+	    warning_at (DECL_SOURCE_LOCATION (decl), OPT_Wvolatile,
+			"%<volatile%>-qualified parameter is "
+			"deprecated");
+
 	  /* Top-level qualifiers on the parameters are
 	     ignored for function types.  */
 	  type = cp_build_qualified_type (type, 0);
diff --git gcc/cp/expr.c gcc/cp/expr.c
index 9160043ed11..939143ddbcc 100644
--- gcc/cp/expr.c
+++ gcc/cp/expr.c
@@ -292,6 +292,11 @@ mark_discarded_use (tree expr)
     case INDIRECT_REF:
     case MEMBER_REF:
       break;
+    case MODIFY_EXPR:
+      /* [expr.ass] says that if the assignment with a volatile-qualified
+	 LHS is a discarded-value expression then it is not deprecated.  */
+      TREE_THIS_VOLATILE (expr) = false;
+      return expr;
     default:
       if (DECL_P (expr))
 	break;
diff --git gcc/cp/typeck.c gcc/cp/typeck.c
index e2a4f285a72..1b456fca652 100644
--- gcc/cp/typeck.c
+++ gcc/cp/typeck.c
@@ -6459,6 +6459,17 @@ cp_build_unary_op (enum tree_code code, tree xarg, bool noconvert,
                              complain))
 	  return error_mark_node;
 
+	/* [depr.volatile.type] "Postfix ++ and -- expressions and
+	   prefix ++ and -- expressions of volatile-qualified arithmetic
+	   and pointer types are deprecated."  */
+	if (TREE_THIS_VOLATILE (arg) || CP_TYPE_VOLATILE_P (TREE_TYPE (arg)))
+	  warning_at (location, OPT_Wvolatile,
+		      "%qs expression of %<volatile%>-qualified type is "
+		      "deprecated",
+		      ((code == PREINCREMENT_EXPR
+			|| code == POSTINCREMENT_EXPR)
+		       ? "++" : "--"));
+
 	/* Forbid using -- or ++ in C++17 on `bool'.  */
 	if (TREE_CODE (declared_type) == BOOLEAN_TYPE)
 	  {
@@ -6538,9 +6549,14 @@ tree
 genericize_compound_lvalue (tree lvalue)
 {
   if (TREE_SIDE_EFFECTS (TREE_OPERAND (lvalue, 0)))
-    lvalue = build2 (TREE_CODE (lvalue), TREE_TYPE (lvalue),
-		     cp_stabilize_reference (TREE_OPERAND (lvalue, 0)),
-		     TREE_OPERAND (lvalue, 1));
+    {
+      const bool was_volatile = TREE_THIS_VOLATILE (lvalue);
+      lvalue = build2_loc (EXPR_LOCATION (lvalue), TREE_CODE (lvalue),
+			   TREE_TYPE (lvalue),
+			   cp_stabilize_reference (TREE_OPERAND (lvalue, 0)),
+			   TREE_OPERAND (lvalue, 1));
+      TREE_THIS_VOLATILE (lvalue) = was_volatile;
+    }
   return build2 (COMPOUND_EXPR, TREE_TYPE (TREE_OPERAND (lvalue, 0)),
 		 lvalue, TREE_OPERAND (lvalue, 0));
 }
@@ -8075,6 +8091,7 @@ cp_build_modify_expr (location_t loc, tree lhs, enum tree_code modifycode,
   tree olhstype = lhstype;
   bool plain_assign = (modifycode == NOP_EXPR);
   bool compound_side_effects_p = false;
+  bool lhs_volatile_p = false;
   tree preeval = NULL_TREE;
 
   /* Avoid duplicate error messages from operands that had errors.  */
@@ -8266,6 +8283,14 @@ cp_build_modify_expr (location_t loc, tree lhs, enum tree_code modifycode,
 	      goto ret;
 	    }
 	  lhstype = olhstype;
+
+	  /* [expr.ass] "A simple assignment whose left operand is of
+	     a volatile-qualified type is deprecated unless the assignment
+	     is either a discarded-value expression or appears in an
+	     unevaluated context."  */
+	  if ((TREE_THIS_VOLATILE (lhs) || CP_TYPE_VOLATILE_P (lhstype))
+	      && !cp_unevaluated_operand)
+	    lhs_volatile_p = true;
 	}
       else
 	{
@@ -8278,6 +8303,15 @@ cp_build_modify_expr (location_t loc, tree lhs, enum tree_code modifycode,
 			 && MAYBE_CLASS_TYPE_P (TREE_TYPE (lhstype)))
 			|| MAYBE_CLASS_TYPE_P (lhstype)));
 
+	  /* An expression of the form E1 op= E2.  [expr.ass] says:
+	     "Such expressions are deprecated if E1 has volatile-qualified
+	     type."  We warn here rather than in cp_genericize_r because
+	     for compound assignments we are supposed to warn even if the
+	     assignment is a discarded-value expression.  */
+	  if (TREE_THIS_VOLATILE (lhs) || CP_TYPE_VOLATILE_P (lhstype))
+	    warning_at (loc, OPT_Wvolatile,
+			"assignment with %<volatile%>-qualified left operand "
+			"is deprecated");
 	  /* Preevaluate the RHS to make sure its evaluation is complete
 	     before the lvalue-to-rvalue conversion of the LHS:
 
@@ -8450,10 +8484,11 @@ cp_build_modify_expr (location_t loc, tree lhs, enum tree_code modifycode,
 	goto ret;
     }
 
-  result = build2 (modifycode == NOP_EXPR ? MODIFY_EXPR : INIT_EXPR,
-		   lhstype, lhs, newrhs);
+  result = build2_loc (loc, modifycode == NOP_EXPR ? MODIFY_EXPR : INIT_EXPR,
+		       lhstype, lhs, newrhs);
 
   TREE_SIDE_EFFECTS (result) = 1;
+  TREE_THIS_VOLATILE (result) = (lhs_volatile_p && modifycode == NOP_EXPR);
   if (!plain_assign)
     TREE_NO_WARNING (result) = 1;
 
diff --git gcc/doc/invoke.texi gcc/doc/invoke.texi
index 7a356840d78..7ca86ce8cda 100644
--- gcc/doc/invoke.texi
+++ gcc/doc/invoke.texi
@@ -243,7 +243,7 @@ in the following sections.
 -Wno-non-template-friend  -Wold-style-cast @gol
 -Woverloaded-virtual  -Wno-pmf-conversions @gol
 -Wno-class-conversion  -Wno-terminate @gol
--Wsign-promo  -Wvirtual-inheritance}
+-Wsign-promo  -Wvirtual-inheritance  -Wvolatile}
 
 @item Objective-C and Objective-C++ Language Options
 @xref{Objective-C and Objective-C++ Dialect Options,,Options Controlling
@@ -3515,6 +3515,18 @@ result in a call to @code{terminate}.
 Disable the warning about the case when a conversion function converts an
 object to the same type, to a base class of that type, or to void; such
 a conversion function will never be called.
+
+@item -Wvolatile @r{(C++ and Objective-C++ only)}
+@opindex Wvolatile
+@opindex Wno-volatile
+Warn about certain uses of volatile qualifier.  This includes postfix
+@code{++} and @code{--} expressions, prefix @code{++} and @code{--}
+expressions, certain assignments where the left operand is a
+volatile-qualified non-class type, volatile-qualified function return
+type, volatile-qualified parameter type, and a structured binding
+of a volatile-qualified type.  This usage was deprecated in C++2a.
+
+Enabled by default with @option{-std=c++2a}.
 @end table
 
 @node Objective-C and Objective-C++ Dialect Options
diff --git gcc/testsuite/c-c++-common/Wbool-operation-1.c gcc/testsuite/c-c++-common/Wbool-operation-1.c
index 04891878155..ce87705692a 100644
--- gcc/testsuite/c-c++-common/Wbool-operation-1.c
+++ gcc/testsuite/c-c++-common/Wbool-operation-1.c
@@ -1,6 +1,7 @@
 /* PR c/77490 */
 /* { dg-do compile } */
 /* { dg-options "-Wall -Wno-psabi" } */
+/* { dg-additional-options "-Wno-volatile" { target c++ } } */
 
 #ifndef __cplusplus
 # define bool _Bool
diff --git gcc/testsuite/c-c++-common/gomp/atomic-1.c gcc/testsuite/c-c++-common/gomp/atomic-1.c
index 3e4bc569ba7..1facf4586f5 100644
--- gcc/testsuite/c-c++-common/gomp/atomic-1.c
+++ gcc/testsuite/c-c++-common/gomp/atomic-1.c
@@ -1,4 +1,5 @@
 /* { dg-do compile } */
+/* { dg-additional-options "-Wno-volatile" { target c++ } } */
 
 int x;
 volatile int y;
diff --git gcc/testsuite/c-c++-common/gomp/atomic-9.c gcc/testsuite/c-c++-common/gomp/atomic-9.c
index c07da8fc712..35548395f36 100644
--- gcc/testsuite/c-c++-common/gomp/atomic-9.c
+++ gcc/testsuite/c-c++-common/gomp/atomic-9.c
@@ -1,5 +1,6 @@
 /* { dg-do compile } */
 /* { dg-options "-fopenmp -fdump-tree-ompexp" } */
+/* { dg-additional-options "-Wno-volatile" { target c++ } } */
 /* { dg-require-effective-target cas_int } */
 
 volatile int *bar(void);
diff --git gcc/testsuite/c-c++-common/gomp/depend-iterator-1.c gcc/testsuite/c-c++-common/gomp/depend-iterator-1.c
index 4fb01c174ec..6fa60215f43 100644
--- gcc/testsuite/c-c++-common/gomp/depend-iterator-1.c
+++ gcc/testsuite/c-c++-common/gomp/depend-iterator-1.c
@@ -1,3 +1,5 @@
+/* { dg-additional-options "-Wno-volatile" { target c++ } } */
+
 int arr[64], arr2[64];
 struct S { int a[4]; } k;
 short arr4[4];
diff --git gcc/testsuite/c-c++-common/gomp/loop-1.c gcc/testsuite/c-c++-common/gomp/loop-1.c
index d2f943aea54..4fb995c02a7 100644
--- gcc/testsuite/c-c++-common/gomp/loop-1.c
+++ gcc/testsuite/c-c++-common/gomp/loop-1.c
@@ -100,8 +100,8 @@ f4 (int *a)
   #pragma omp loop order(concurrent) bind(parallel)
   for (i = 0; i < 64; i++)
     {
-      #pragma omp atomic read
-      a[i] = v;				/* { dg-error "OpenMP constructs other than 'parallel', 'loop' or 'simd' may not be nested inside a 'loop' region" } */
+      #pragma omp atomic read		/* { dg-error "OpenMP constructs other than 'parallel', 'loop' or 'simd' may not be nested inside a 'loop' region" "" { target c++ } } */
+      a[i] = v;				/* { dg-error "OpenMP constructs other than 'parallel', 'loop' or 'simd' may not be nested inside a 'loop' region" "" { target c } } */
     }
   #pragma omp loop order(concurrent) bind(parallel)
   for (i = 0; i < 64; i++)
@@ -172,8 +172,8 @@ f5 (int *a)
   #pragma omp loop
   for (i = 0; i < 64; i++)
     {
-      #pragma omp atomic read
-      a[i] = v;				/* { dg-error "OpenMP constructs other than 'parallel', 'loop' or 'simd' may not be nested inside a 'loop' region" } */
+      #pragma omp atomic read		/* { dg-error "OpenMP constructs other than 'parallel', 'loop' or 'simd' may not be nested inside a 'loop' region" "" { target c++ } } */
+      a[i] = v;				/* { dg-error "OpenMP constructs other than 'parallel', 'loop' or 'simd' may not be nested inside a 'loop' region" "" { target c } } */
     }
   #pragma omp loop
   for (i = 0; i < 64; i++)
@@ -245,8 +245,8 @@ f6 (int *a)
   #pragma omp loop
   for (i = 0; i < 64; i++)
     {
-      #pragma omp atomic read
-      a[i] = v;				/* { dg-error "OpenMP constructs other than 'parallel', 'loop' or 'simd' may not be nested inside a 'loop' region" } */
+      #pragma omp atomic read		/* { dg-error "OpenMP constructs other than 'parallel', 'loop' or 'simd' may not be nested inside a 'loop' region" "" { target c++ } } */
+      a[i] = v;				/* { dg-error "OpenMP constructs other than 'parallel', 'loop' or 'simd' may not be nested inside a 'loop' region" "" { target c } } */
     }
   #pragma omp loop
   for (i = 0; i < 64; i++)
diff --git gcc/testsuite/c-c++-common/gomp/order-3.c gcc/testsuite/c-c++-common/gomp/order-3.c
index 2d51bf37749..e33386dd5cc 100644
--- gcc/testsuite/c-c++-common/gomp/order-3.c
+++ gcc/testsuite/c-c++-common/gomp/order-3.c
@@ -50,8 +50,8 @@ f1 (int *a)
   #pragma omp simd order(concurrent)
   for (i = 0; i < 64; i++)
     {
-      #pragma omp atomic read
-      a[i] = v;				/* { dg-error "OpenMP constructs other than 'parallel', 'loop' or 'simd' may not be nested inside a region with the 'order\\(concurrent\\)' clause" } */
+      #pragma omp atomic read		/* { dg-error "OpenMP constructs other than 'parallel', 'loop' or 'simd' may not be nested inside a region with the 'order\\(concurrent\\)' clause" "" { target c++ } } */
+      a[i] = v;				/* { dg-error "OpenMP constructs other than 'parallel', 'loop' or 'simd' may not be nested inside a region with the 'order\\(concurrent\\)' clause" "" { target c } } */
     }
   #pragma omp simd order(concurrent)
   for (i = 0; i < 64; i++)
@@ -112,8 +112,8 @@ f2 (int *a)
   #pragma omp for simd order(concurrent)
   for (i = 0; i < 64; i++)
     {
-      #pragma omp atomic read
-      a[i] = v;				/* { dg-error "OpenMP constructs other than 'parallel', 'loop' or 'simd' may not be nested inside a region with the 'order\\(concurrent\\)' clause" } */
+      #pragma omp atomic read		/* { dg-error "OpenMP constructs other than 'parallel', 'loop' or 'simd' may not be nested inside a region with the 'order\\(concurrent\\)' clause" "" { target c++ } } */
+      a[i] = v;				/* { dg-error "OpenMP constructs other than 'parallel', 'loop' or 'simd' may not be nested inside a region with the 'order\\(concurrent\\)' clause" "" { target c } } */
     }
   #pragma omp for simd order(concurrent)
   for (i = 0; i < 64; i++)
@@ -174,8 +174,8 @@ f3 (int *a)
   #pragma omp for order(concurrent)
   for (i = 0; i < 64; i++)
     {
-      #pragma omp atomic read
-      a[i] = v;				/* { dg-error "OpenMP constructs other than 'parallel', 'loop' or 'simd' may not be nested inside a region with the 'order\\(concurrent\\)' clause" } */
+      #pragma omp atomic read		/* { dg-error "OpenMP constructs other than 'parallel', 'loop' or 'simd' may not be nested inside a region with the 'order\\(concurrent\\)' clause" "" { target c++ } } */
+      a[i] = v;				/* { dg-error "OpenMP constructs other than 'parallel', 'loop' or 'simd' may not be nested inside a region with the 'order\\(concurrent\\)' clause" "" { target c } } */
     }
   #pragma omp for order(concurrent)
   for (i = 0; i < 64; i++)
diff --git gcc/testsuite/c-c++-common/pr69733.c gcc/testsuite/c-c++-common/pr69733.c
index 57ec1eccb9f..ab70f49009c 100644
--- gcc/testsuite/c-c++-common/pr69733.c
+++ gcc/testsuite/c-c++-common/pr69733.c
@@ -1,5 +1,6 @@
 /* { dg-do compile } */
 /* { dg-options "-W -fdiagnostics-show-caret" } */
+/* { dg-additional-options "-Wno-volatile" { target c++ } } */
 
 typedef const double cd;
 double val;
@@ -21,4 +22,3 @@ cd val2() {return val;} /* { dg-warning "qualifiers ignored" } */
  cd val2() {return val;}
  ^~
 { dg-end-multiline-output "" } */
-
diff --git gcc/testsuite/c-c++-common/spec-barrier-2.c gcc/testsuite/c-c++-common/spec-barrier-2.c
index b09567e62a9..a27ec54f0d3 100644
--- gcc/testsuite/c-c++-common/spec-barrier-2.c
+++ gcc/testsuite/c-c++-common/spec-barrier-2.c
@@ -1,4 +1,5 @@
 /* { dg-do run } */
+/* { dg-additional-options "-Wno-volatile" { target c++ } } */
 
 /* Even on targets that don't need the optional failval parameter,
    side-effects on the operand should still be calculated.  */
diff --git gcc/testsuite/c-c++-common/tm/pr54893.c gcc/testsuite/c-c++-common/tm/pr54893.c
index 3766078d31e..266cbe9c652 100644
--- gcc/testsuite/c-c++-common/tm/pr54893.c
+++ gcc/testsuite/c-c++-common/tm/pr54893.c
@@ -1,5 +1,6 @@
 /* { dg-do compile } */
 /* { dg-options "-fgnu-tm -fdump-ipa-tmipa" } */
+/* { dg-additional-options "-Wno-volatile" { target c++ } } */
 
 /* Test that volatiles are allowed inside relaxed transactions.  */
 
diff --git gcc/testsuite/g++.dg/cpp0x/pr65327.C gcc/testsuite/g++.dg/cpp0x/pr65327.C
index 5176b3c3204..6e888ebff2c 100644
--- gcc/testsuite/g++.dg/cpp0x/pr65327.C
+++ gcc/testsuite/g++.dg/cpp0x/pr65327.C
@@ -11,7 +11,7 @@ foo ()
   static constexpr volatile int k = 5;
 }
 
-constexpr volatile int
+constexpr volatile int // { dg-warning "deprecated" "" { target c++2a } }
 bar ()
 {
   return i;
diff --git gcc/testsuite/g++.dg/cpp0x/rv-conv2.C gcc/testsuite/g++.dg/cpp0x/rv-conv2.C
index 9b9b154995b..2f2a1fa702a 100644
--- gcc/testsuite/g++.dg/cpp0x/rv-conv2.C
+++ gcc/testsuite/g++.dg/cpp0x/rv-conv2.C
@@ -1,16 +1,16 @@
 // PR c++/89705
 // { dg-do compile { target c++11 } }
 
-struct W { operator const volatile int(); };
+struct W { operator const volatile int(); }; // { dg-warning "deprecated" "" { target c++2a } }
 const int& rci = W();
 
 struct X { operator const int(); };
 int&& rri = X();
 
-struct Y { operator volatile int(); };
+struct Y { operator volatile int(); }; // { dg-warning "deprecated" "" { target c++2a } }
 int&& rri2 = Y();
 
-struct Z { operator const volatile int(); };
+struct Z { operator const volatile int(); }; // { dg-warning "deprecated" "" { target c++2a } }
 volatile int&& rri3 = Z();
 
 enum E { A };
diff --git gcc/testsuite/g++.dg/cpp0x/rv1n.C gcc/testsuite/g++.dg/cpp0x/rv1n.C
index f5e75681758..a762fc85862 100644
--- gcc/testsuite/g++.dg/cpp0x/rv1n.C
+++ gcc/testsuite/g++.dg/cpp0x/rv1n.C
@@ -26,8 +26,8 @@ struct A
 
                A    source();
 const          A  c_source();
-      volatile A  v_source();
-const volatile A cv_source();
+      volatile A  v_source(); // { dg-warning "deprecated" "" { target c++2a } }
+const volatile A cv_source(); // { dg-warning "deprecated" "" { target c++2a } }
 
 // 1 at a time
 
diff --git gcc/testsuite/g++.dg/cpp0x/rv1p.C gcc/testsuite/g++.dg/cpp0x/rv1p.C
index a9097276d5a..e2a983a7708 100644
--- gcc/testsuite/g++.dg/cpp0x/rv1p.C
+++ gcc/testsuite/g++.dg/cpp0x/rv1p.C
@@ -26,8 +26,8 @@ struct A
 
                A    source();
 const          A  c_source();
-      volatile A  v_source();
-const volatile A cv_source();
+      volatile A  v_source(); // { dg-warning "deprecated" "" { target c++2a } }
+const volatile A cv_source(); // { dg-warning "deprecated" "" { target c++2a } }
 
 // 1 at a time
 
diff --git gcc/testsuite/g++.dg/cpp0x/rv2n.C gcc/testsuite/g++.dg/cpp0x/rv2n.C
index 65eda80fba0..2871ccf9ab3 100644
--- gcc/testsuite/g++.dg/cpp0x/rv2n.C
+++ gcc/testsuite/g++.dg/cpp0x/rv2n.C
@@ -25,8 +25,8 @@ struct A
 
                A    source();
 const          A  c_source();
-      volatile A  v_source();
-const volatile A cv_source();
+      volatile A  v_source(); // { dg-warning "deprecated" "" { target c++2a } }
+const volatile A cv_source(); // { dg-warning "deprecated" "" { target c++2a } }
 
 // 2 at a time
 
diff --git gcc/testsuite/g++.dg/cpp0x/rv2p.C gcc/testsuite/g++.dg/cpp0x/rv2p.C
index 25a42ba2af8..bab0dce3d97 100644
--- gcc/testsuite/g++.dg/cpp0x/rv2p.C
+++ gcc/testsuite/g++.dg/cpp0x/rv2p.C
@@ -25,8 +25,8 @@ struct A
 
                A    source();
 const          A  c_source();
-      volatile A  v_source();
-const volatile A cv_source();
+      volatile A  v_source(); // { dg-warning "deprecated" "" { target c++2a } }
+const volatile A cv_source(); // { dg-warning "deprecated" "" { target c++2a } }
 
 // 2 at a time
 
diff --git gcc/testsuite/g++.dg/cpp0x/rv3n.C gcc/testsuite/g++.dg/cpp0x/rv3n.C
index 4549438f8ef..35cdba95858 100644
--- gcc/testsuite/g++.dg/cpp0x/rv3n.C
+++ gcc/testsuite/g++.dg/cpp0x/rv3n.C
@@ -25,8 +25,8 @@ struct A
 
                A    source();
 const          A  c_source();
-      volatile A  v_source();
-const volatile A cv_source();
+      volatile A  v_source(); // { dg-warning "deprecated" "" { target c++2a } }
+const volatile A cv_source(); // { dg-warning "deprecated" "" { target c++2a } }
 
 // 3 at a time
 
diff --git gcc/testsuite/g++.dg/cpp0x/rv3p.C gcc/testsuite/g++.dg/cpp0x/rv3p.C
index 2d7d78df6be..b25aa26c9b0 100644
--- gcc/testsuite/g++.dg/cpp0x/rv3p.C
+++ gcc/testsuite/g++.dg/cpp0x/rv3p.C
@@ -25,8 +25,8 @@ struct A
 
                A    source();
 const          A  c_source();
-      volatile A  v_source();
-const volatile A cv_source();
+      volatile A  v_source(); // { dg-warning "deprecated" "" { target c++2a } }
+const volatile A cv_source(); // { dg-warning "deprecated" "" { target c++2a } }
 
 // 3 at a time
 
diff --git gcc/testsuite/g++.dg/cpp0x/rv4n.C gcc/testsuite/g++.dg/cpp0x/rv4n.C
index 29deb3fc81b..6941a13de6c 100644
--- gcc/testsuite/g++.dg/cpp0x/rv4n.C
+++ gcc/testsuite/g++.dg/cpp0x/rv4n.C
@@ -25,8 +25,8 @@ struct A
 
                A    source();
 const          A  c_source();
-      volatile A  v_source();
-const volatile A cv_source();
+      volatile A  v_source(); // { dg-warning "deprecated" "" { target c++2a } }
+const volatile A cv_source(); // { dg-warning "deprecated" "" { target c++2a } }
 
 // 4 at a time
 
diff --git gcc/testsuite/g++.dg/cpp0x/rv4p.C gcc/testsuite/g++.dg/cpp0x/rv4p.C
index 0e4903bc291..cd0d631d780 100644
--- gcc/testsuite/g++.dg/cpp0x/rv4p.C
+++ gcc/testsuite/g++.dg/cpp0x/rv4p.C
@@ -25,8 +25,8 @@ struct A
 
                A    source();
 const          A  c_source();
-      volatile A  v_source();
-const volatile A cv_source();
+      volatile A  v_source(); // { dg-warning "deprecated" "" { target c++2a } }
+const volatile A cv_source(); // { dg-warning "deprecated" "" { target c++2a } }
 
 // 4 at a time
 
diff --git gcc/testsuite/g++.dg/cpp0x/rv5n.C gcc/testsuite/g++.dg/cpp0x/rv5n.C
index f11d07a3921..086aa460c68 100644
--- gcc/testsuite/g++.dg/cpp0x/rv5n.C
+++ gcc/testsuite/g++.dg/cpp0x/rv5n.C
@@ -25,8 +25,8 @@ struct A
 
                A    source();
 const          A  c_source();
-      volatile A  v_source();
-const volatile A cv_source();
+      volatile A  v_source(); // { dg-warning "deprecated" "" { target c++2a } }
+const volatile A cv_source(); // { dg-warning "deprecated" "" { target c++2a } }
 
 // 5 at a time
 
diff --git gcc/testsuite/g++.dg/cpp0x/rv5p.C gcc/testsuite/g++.dg/cpp0x/rv5p.C
index 63441a3f0da..34c1017f578 100644
--- gcc/testsuite/g++.dg/cpp0x/rv5p.C
+++ gcc/testsuite/g++.dg/cpp0x/rv5p.C
@@ -25,8 +25,8 @@ struct A
 
                A    source();
 const          A  c_source();
-      volatile A  v_source();
-const volatile A cv_source();
+      volatile A  v_source(); // { dg-warning "deprecated" "" { target c++2a } }
+const volatile A cv_source(); // { dg-warning "deprecated" "" { target c++2a } }
 
 // 5 at a time
 
diff --git gcc/testsuite/g++.dg/cpp0x/rv6n.C gcc/testsuite/g++.dg/cpp0x/rv6n.C
index 0ebbe33e1d1..b21d22a5b87 100644
--- gcc/testsuite/g++.dg/cpp0x/rv6n.C
+++ gcc/testsuite/g++.dg/cpp0x/rv6n.C
@@ -25,8 +25,8 @@ struct A
 
                A    source();
 const          A  c_source();
-      volatile A  v_source();
-const volatile A cv_source();
+      volatile A  v_source(); // { dg-warning "deprecated" "" { target c++2a } }
+const volatile A cv_source(); // { dg-warning "deprecated" "" { target c++2a } }
 
 // 6 at a time
 
diff --git gcc/testsuite/g++.dg/cpp0x/rv6p.C gcc/testsuite/g++.dg/cpp0x/rv6p.C
index 26714f0c9aa..fee692bb08f 100644
--- gcc/testsuite/g++.dg/cpp0x/rv6p.C
+++ gcc/testsuite/g++.dg/cpp0x/rv6p.C
@@ -25,8 +25,8 @@ struct A
 
                A    source();
 const          A  c_source();
-      volatile A  v_source();
-const volatile A cv_source();
+      volatile A  v_source(); // { dg-warning "deprecated" "" { target c++2a } }
+const volatile A cv_source(); // { dg-warning "deprecated" "" { target c++2a } }
 
 // 6 at a time
 
diff --git gcc/testsuite/g++.dg/cpp0x/rv7n.C gcc/testsuite/g++.dg/cpp0x/rv7n.C
index d9e371b8adb..5bc313cc07f 100644
--- gcc/testsuite/g++.dg/cpp0x/rv7n.C
+++ gcc/testsuite/g++.dg/cpp0x/rv7n.C
@@ -25,8 +25,8 @@ struct A
 
                A    source();
 const          A  c_source();
-      volatile A  v_source();
-const volatile A cv_source();
+      volatile A  v_source(); // { dg-warning "deprecated" "" { target c++2a } }
+const volatile A cv_source(); // { dg-warning "deprecated" "" { target c++2a } }
 
 // 7 at a time
 
diff --git gcc/testsuite/g++.dg/cpp0x/rv7p.C gcc/testsuite/g++.dg/cpp0x/rv7p.C
index 60a35835c7d..b0b8f965498 100644
--- gcc/testsuite/g++.dg/cpp0x/rv7p.C
+++ gcc/testsuite/g++.dg/cpp0x/rv7p.C
@@ -25,8 +25,8 @@ struct A
 
                A    source();
 const          A  c_source();
-      volatile A  v_source();
-const volatile A cv_source();
+      volatile A  v_source(); // { dg-warning "deprecated" "" { target c++2a } }
+const volatile A cv_source(); // { dg-warning "deprecated" "" { target c++2a } }
 
 // 7 at a time
 
diff --git gcc/testsuite/g++.dg/cpp0x/rv8p.C gcc/testsuite/g++.dg/cpp0x/rv8p.C
index e12da4b8d79..287fb93b432 100644
--- gcc/testsuite/g++.dg/cpp0x/rv8p.C
+++ gcc/testsuite/g++.dg/cpp0x/rv8p.C
@@ -25,8 +25,8 @@ struct A
 
                A    source();
 const          A  c_source();
-      volatile A  v_source();
-const volatile A cv_source();
+      volatile A  v_source(); // { dg-warning "deprecated" "" { target c++2a } }
+const volatile A cv_source(); // { dg-warning "deprecated" "" { target c++2a } }
 
 // 8 at a time
 
diff --git gcc/testsuite/g++.dg/cpp0x/trailing14.C gcc/testsuite/g++.dg/cpp0x/trailing14.C
index 2544d0bab5e..4ebb37406ad 100644
--- gcc/testsuite/g++.dg/cpp0x/trailing14.C
+++ gcc/testsuite/g++.dg/cpp0x/trailing14.C
@@ -1,6 +1,6 @@
 // PR c++/65775
 // { dg-do compile { target c++11 } }
-// { dg-options "-Wignored-qualifiers" }
+// { dg-options "-Wignored-qualifiers -Wno-volatile" }
 
 using Qi = int const volatile;
 Qi q1();           // { dg-warning "1: type qualifiers ignored" }
diff --git gcc/testsuite/g++.dg/cpp1y/new1.C gcc/testsuite/g++.dg/cpp1y/new1.C
index 5e4f1bf6b0b..b9ad64dfcc0 100644
--- gcc/testsuite/g++.dg/cpp1y/new1.C
+++ gcc/testsuite/g++.dg/cpp1y/new1.C
@@ -65,7 +65,7 @@ void
 test_unused() {
   volatile double d = 0.0;
   double *p = new double ();
-  d += 1.0;
+  d += 1.0; // { dg-warning "deprecated" "" { target c++2a } }
   delete p;
 }
 
diff --git gcc/testsuite/g++.dg/cpp2a/volatile1.C gcc/testsuite/g++.dg/cpp2a/volatile1.C
new file mode 100644
index 00000000000..16c3bb417d3
--- /dev/null
+++ gcc/testsuite/g++.dg/cpp2a/volatile1.C
@@ -0,0 +1,140 @@
+// PR c++/91361 - P1152R4: Deprecating some uses of volatile.
+// { dg-do compile { target c++17 } }
+
+#define ACCESS_ONCE(x) (*(volatile __typeof(x) *)&(x))
+
+struct S {
+  volatile int a : 4;
+  int b : 2;
+};
+
+struct T {
+  int a : 4;
+  int b : 2;
+};
+
+union U {
+  char c;
+  int i;
+};
+
+struct W {
+  W();
+  W(volatile W&);
+  W& operator=(volatile W&) volatile;
+};
+
+volatile int // { dg-warning ".volatile.-qualified return type is deprecated" "" { target c++2a } }
+fn (volatile int i) // { dg-warning ".volatile.-qualified parameter is deprecated" "" { target c++2a } }
+{
+  volatile int v = 10;
+  int *volatile p = nullptr;
+
+  // Pre/post ++/--.
+  v++; // { dg-warning "expression of .volatile.-qualified type is deprecated" "" { target c++2a } }
+  ++v; // { dg-warning "expression of .volatile.-qualified type is deprecated" "" { target c++2a } }
+  v--; // { dg-warning "expression of .volatile.-qualified type is deprecated" "" { target c++2a } }
+  --v; // { dg-warning "expression of .volatile.-qualified type is deprecated" "" { target c++2a } }
+  p++; // { dg-warning "expression of .volatile.-qualified type is deprecated" "" { target c++2a } }
+  ++p; // { dg-warning "expression of .volatile.-qualified type is deprecated" "" { target c++2a } }
+  p--; // { dg-warning "expression of .volatile.-qualified type is deprecated" "" { target c++2a } }
+  --p; // { dg-warning "expression of .volatile.-qualified type is deprecated" "" { target c++2a } }
+  return v + i + *p;
+}
+
+void
+fn2 ()
+{
+  volatile int vi = 42;
+  int i = 24;
+
+  // Discarded-value expression ([expr.context]).
+  // The lvalue-to-rvalue conversion is applied here:
+  vi;
+  // ...but not here.  Otherwise we'd write to VI and then immediately read it.
+  vi = 42;
+  vi = i;
+  vi = i = 42;
+  i = vi = 42; // { dg-warning "assignment with .volatile.-qualified left operand is deprecated" "" { target c++2a } }
+  &(vi = i); // { dg-warning "assignment with .volatile.-qualified left operand is deprecated" "" { target c++2a } }
+  (vi = 42, 45);
+  (i = vi = 42, 10); // { dg-warning "assignment with .volatile.-qualified left operand is deprecated" "" { target c++2a } }
+  i = vi; // LHS not volatile.
+  i = (vi = i, 42);
+  static_cast<void>(vi = i);
+  static_cast<void>(i = vi = 42); // { dg-warning "assignment with .volatile.-qualified left operand is deprecated" "" { target c++2a } }
+  (void)(vi = i);
+  (void)(i = vi = 42); // { dg-warning "assignment with .volatile.-qualified left operand is deprecated" "" { target c++2a } }
+
+  // Unevaluated operand.
+  decltype(vi = 42) x = vi;
+
+  // Compound assignments.
+  vi += i; // { dg-warning "assignment with .volatile.-qualified left operand is deprecated" "" { target c++2a } }
+  vi -= i; // { dg-warning "assignment with .volatile.-qualified left operand is deprecated" "" { target c++2a } }
+  vi %= i; // { dg-warning "assignment with .volatile.-qualified left operand is deprecated" "" { target c++2a } }
+  vi ^= i; // { dg-warning "assignment with .volatile.-qualified left operand is deprecated" "" { target c++2a } }
+  vi |= i; // { dg-warning "assignment with .volatile.-qualified left operand is deprecated" "" { target c++2a } }
+  vi /= i; // { dg-warning "assignment with .volatile.-qualified left operand is deprecated" "" { target c++2a } }
+  vi = vi += 42; // { dg-warning "assignment with .volatile.-qualified left operand is deprecated" "" { target c++2a } }
+  vi += vi = 42; // { dg-warning "assignment with .volatile.-qualified left operand is deprecated" "" { target c++2a } }
+  i *= vi;
+  decltype(vi -= 42) x2 = vi; // { dg-warning "assignment with .volatile.-qualified left operand is deprecated" "" { target c++2a } }
+
+  // Structured bindings.
+  int a[] = { 10, 5 };
+  const auto & [cxr, cyr] = a;
+  const volatile auto & [cvxr, cvyr] = a; // { dg-warning ".volatile.-qualified structured binding is deprecated" "" { target c++2a } }
+  volatile auto & [vxr, vyr] = a; // { dg-warning ".volatile.-qualified structured binding is deprecated" "" { target c++2a } }
+}
+
+void
+fn3 ()
+{
+  volatile int i, j, k = 0;
+  i = j = k; // { dg-warning "assignment with .volatile.-qualified left operand is deprecated" "" { target c++2a } }
+
+  ACCESS_ONCE(j);
+
+  S s;
+  s.b = 1;
+
+  volatile U u;
+  u.c = 42;
+  i = u.c = 42; // { dg-warning "assignment with .volatile.-qualified left operand is deprecated" "" { target c++2a } }
+  u.c += 42; // { dg-warning "assignment with .volatile.-qualified left operand is deprecated" "" { target c++2a } }
+
+  volatile T t;
+  t.a = 3;
+  j = t.a = 3; // { dg-warning "assignment with .volatile.-qualified left operand is deprecated" "" { target c++2a } }
+  t.a += 3; // { dg-warning "assignment with .volatile.-qualified left operand is deprecated" "" { target c++2a } }
+
+  volatile int *src = &i;
+  *src; // No assignment, don't warn.
+}
+
+void
+fn4 ()
+{
+  volatile W vw;
+  W w;
+  // Assignment to objects of a class is defined by the copy/move assignment
+  // operator.
+  vw = w;
+  w = vw;
+}
+
+template<typename T>
+void raccoon ()
+{
+  volatile T t, u;
+  t = 42;
+  u = t = 42; // { dg-warning "assignment with .volatile.-qualified left operand is deprecated" "" { target c++2a } }
+  t &= 42; // { dg-warning "assignment with .volatile.-qualified left operand is deprecated" "" { target c++2a } }
+}
+
+void
+fn5 ()
+{
+  raccoon<int>();
+}
diff --git gcc/testsuite/g++.dg/cpp2a/volatile2.C gcc/testsuite/g++.dg/cpp2a/volatile2.C
new file mode 100644
index 00000000000..31035e22d8f
--- /dev/null
+++ gcc/testsuite/g++.dg/cpp2a/volatile2.C
@@ -0,0 +1,141 @@
+// PR c++/91361 - P1152R4: Deprecating some uses of volatile.
+// { dg-do compile { target c++2a } }
+// { dg-options "-Wno-volatile" }
+
+#define ACCESS_ONCE(x) (*(volatile __typeof(x) *)&(x))
+
+struct S {
+  volatile int a : 4;
+  int b : 2;
+};
+
+struct T {
+  int a : 4;
+  int b : 2;
+};
+
+union U {
+  char c;
+  int i;
+};
+
+struct W {
+  W();
+  W(volatile W&);
+  W& operator=(volatile W&) volatile;
+};
+
+volatile int
+fn (volatile int i)
+{
+  volatile int v = 10;
+  int *volatile p = nullptr;
+
+  // Pre/post ++/--.
+  v++;
+  ++v;
+  v--;
+  --v;
+  p++;
+  ++p;
+  p--;
+  --p;
+  return v + i + *p;
+}
+
+void
+fn2 ()
+{
+  volatile int vi = 42;
+  int i = 24;
+
+  // Discarded-value expression ([expr.context]).
+  // The lvalue-to-rvalue conversion is applied here:
+  vi;
+  // ...but not here.  Otherwise we'd write to VI and then immediately read it.
+  vi = 42;
+  vi = i;
+  vi = i = 42;
+  i = vi = 42;
+  &(vi = i);
+  (vi = 42, 45);
+  (i = vi = 42, 10);
+  i = vi; // LHS not volatile.
+  i = (vi = i, 42);
+  static_cast<void>(vi = i);
+  static_cast<void>(i = vi = 42);
+  (void)(vi = i);
+  (void)(i = vi = 42);
+
+  // Unevaluated operand.
+  decltype(vi = 42) x = vi;
+
+  // Compound assignments.
+  vi += i;
+  vi -= i;
+  vi %= i;
+  vi ^= i;
+  vi |= i;
+  vi /= i;
+  vi = vi += 42;
+  vi += vi = 42;
+  i *= vi;
+  decltype(vi -= 42) x2 = vi;
+
+  // Structured bindings.
+  int a[] = { 10, 5 };
+  const auto & [cxr, cyr] = a;
+  const volatile auto & [cvxr, cvyr] = a;
+  volatile auto & [vxr, vyr] = a;
+}
+
+void
+fn3 ()
+{
+  volatile int i, j, k = 0;
+  i = j = k;
+
+  ACCESS_ONCE(j);
+
+  S s;
+  s.b = 1;
+
+  volatile U u;
+  u.c = 42;
+  i = u.c = 42;
+  u.c += 42;
+
+  volatile T t;
+  t.a = 3;
+  j = t.a = 3;
+  t.a += 3;
+
+  volatile int *src = &i;
+  *src; // No assignment, don't warn.
+}
+
+void
+fn4 ()
+{
+  volatile W vw;
+  W w;
+  // Assignment to objects of a class is defined by the copy/move assignment
+  // operator.
+  vw = w;
+  w = vw;
+}
+
+template<typename T>
+void raccoon ()
+{
+  volatile T t, u;
+  t = 42;
+  u = t = 42;
+  t &= 42;
+}
+
+void
+fn5 ()
+{
+  raccoon<int>();
+}
diff --git gcc/testsuite/g++.dg/cpp2a/volatile3.C gcc/testsuite/g++.dg/cpp2a/volatile3.C
new file mode 100644
index 00000000000..731c9aec99f
--- /dev/null
+++ gcc/testsuite/g++.dg/cpp2a/volatile3.C
@@ -0,0 +1,141 @@
+// PR c++/91361 - P1152R4: Deprecating some uses of volatile.
+// { dg-do compile { target c++17 } }
+// { dg-options "-Wvolatile" }
+
+#define ACCESS_ONCE(x) (*(volatile __typeof(x) *)&(x))
+
+struct S {
+  volatile int a : 4;
+  int b : 2;
+};
+
+struct T {
+  int a : 4;
+  int b : 2;
+};
+
+union U {
+  char c;
+  int i;
+};
+
+struct W {
+  W();
+  W(volatile W&);
+  W& operator=(volatile W&) volatile;
+};
+
+volatile int // { dg-warning ".volatile.-qualified return type is deprecated" }
+fn (volatile int i) // { dg-warning ".volatile.-qualified parameter is deprecated" }
+{
+  volatile int v = 10;
+  int *volatile p = nullptr;
+
+  // Pre/post ++/--.
+  v++; // { dg-warning "expression of .volatile.-qualified type is deprecated" }
+  ++v; // { dg-warning "expression of .volatile.-qualified type is deprecated" }
+  v--; // { dg-warning "expression of .volatile.-qualified type is deprecated" }
+  --v; // { dg-warning "expression of .volatile.-qualified type is deprecated" }
+  p++; // { dg-warning "expression of .volatile.-qualified type is deprecated" }
+  ++p; // { dg-warning "expression of .volatile.-qualified type is deprecated" }
+  p--; // { dg-warning "expression of .volatile.-qualified type is deprecated" }
+  --p; // { dg-warning "expression of .volatile.-qualified type is deprecated" }
+  return v + i + *p;
+}
+
+void
+fn2 ()
+{
+  volatile int vi = 42;
+  int i = 24;
+
+  // Discarded-value expression ([expr.context]).
+  // The lvalue-to-rvalue conversion is applied here:
+  vi;
+  // ...but not here.  Otherwise we'd write to VI and then immediately read it.
+  vi = 42;
+  vi = i;
+  vi = i = 42;
+  i = vi = 42; // { dg-warning "assignment with .volatile.-qualified left operand is deprecated" }
+  &(vi = i); // { dg-warning "assignment with .volatile.-qualified left operand is deprecated" }
+  (vi = 42, 45);
+  (i = vi = 42, 10); // { dg-warning "assignment with .volatile.-qualified left operand is deprecated" }
+  i = vi; // LHS not volatile.
+  i = (vi = i, 42);
+  static_cast<void>(vi = i);
+  static_cast<void>(i = vi = 42); // { dg-warning "assignment with .volatile.-qualified left operand is deprecated" }
+  (void)(vi = i);
+  (void)(i = vi = 42); // { dg-warning "assignment with .volatile.-qualified left operand is deprecated" }
+
+  // Unevaluated operand.
+  decltype(vi = 42) x = vi;
+
+  // Compound assignments.
+  vi += i; // { dg-warning "assignment with .volatile.-qualified left operand is deprecated" }
+  vi -= i; // { dg-warning "assignment with .volatile.-qualified left operand is deprecated" }
+  vi %= i; // { dg-warning "assignment with .volatile.-qualified left operand is deprecated" }
+  vi ^= i; // { dg-warning "assignment with .volatile.-qualified left operand is deprecated" }
+  vi |= i; // { dg-warning "assignment with .volatile.-qualified left operand is deprecated" }
+  vi /= i; // { dg-warning "assignment with .volatile.-qualified left operand is deprecated" }
+  vi = vi += 42; // { dg-warning "assignment with .volatile.-qualified left operand is deprecated" }
+  vi += vi = 42; // { dg-warning "assignment with .volatile.-qualified left operand is deprecated" }
+  i *= vi;
+  decltype(vi -= 42) x2 = vi; // { dg-warning "assignment with .volatile.-qualified left operand is deprecated" }
+
+  // Structured bindings.
+  int a[] = { 10, 5 };
+  const auto & [cxr, cyr] = a;
+  const volatile auto & [cvxr, cvyr] = a; // { dg-warning ".volatile.-qualified structured binding is deprecated" }
+  volatile auto & [vxr, vyr] = a; // { dg-warning ".volatile.-qualified structured binding is deprecated" }
+}
+
+void
+fn3 ()
+{
+  volatile int i, j, k = 0;
+  i = j = k; // { dg-warning "assignment with .volatile.-qualified left operand is deprecated" }
+
+  ACCESS_ONCE(j);
+
+  S s;
+  s.b = 1;
+
+  volatile U u;
+  u.c = 42;
+  i = u.c = 42; // { dg-warning "assignment with .volatile.-qualified left operand is deprecated" }
+  u.c += 42; // { dg-warning "assignment with .volatile.-qualified left operand is deprecated" }
+
+  volatile T t;
+  t.a = 3;
+  j = t.a = 3; // { dg-warning "assignment with .volatile.-qualified left operand is deprecated" }
+  t.a += 3; // { dg-warning "assignment with .volatile.-qualified left operand is deprecated" }
+
+  volatile int *src = &i;
+  *src; // No assignment, don't warn.
+}
+
+void
+fn4 ()
+{
+  volatile W vw;
+  W w;
+  // Assignment to objects of a class is defined by the copy/move assignment
+  // operator.
+  vw = w;
+  w = vw;
+}
+
+template<typename T>
+void raccoon ()
+{
+  volatile T t, u;
+  t = 42;
+  u = t = 42; // { dg-warning "assignment with .volatile.-qualified left operand is deprecated" }
+  t &= 42; // { dg-warning "assignment with .volatile.-qualified left operand is deprecated" }
+}
+
+void
+fn5 ()
+{
+  raccoon<int>();
+}
diff --git gcc/testsuite/g++.dg/cpp2a/volatile4.C gcc/testsuite/g++.dg/cpp2a/volatile4.C
new file mode 100644
index 00000000000..4d039545ac9
--- /dev/null
+++ gcc/testsuite/g++.dg/cpp2a/volatile4.C
@@ -0,0 +1,141 @@
+// PR c++/91361 - P1152R4: Deprecating some uses of volatile.
+// { dg-do compile { target c++2a } }
+// { dg-options "-Wno-deprecated" }
+
+#define ACCESS_ONCE(x) (*(volatile __typeof(x) *)&(x))
+
+struct S {
+  volatile int a : 4;
+  int b : 2;
+};
+
+struct T {
+  int a : 4;
+  int b : 2;
+};
+
+union U {
+  char c;
+  int i;
+};
+
+struct W {
+  W();
+  W(volatile W&);
+  W& operator=(volatile W&) volatile;
+};
+
+volatile int
+fn (volatile int i)
+{
+  volatile int v = 10;
+  int *volatile p = nullptr;
+
+  // Pre/post ++/--.
+  v++;
+  ++v;
+  v--;
+  --v;
+  p++;
+  ++p;
+  p--;
+  --p;
+  return v + i + *p;
+}
+
+void
+fn2 ()
+{
+  volatile int vi = 42;
+  int i = 24;
+
+  // Discarded-value expression ([expr.context]).
+  // The lvalue-to-rvalue conversion is applied here:
+  vi;
+  // ...but not here.  Otherwise we'd write to VI and then immediately read it.
+  vi = 42;
+  vi = i;
+  vi = i = 42;
+  i = vi = 42;
+  &(vi = i);
+  (vi = 42, 45);
+  (i = vi = 42, 10);
+  i = vi; // LHS not volatile.
+  i = (vi = i, 42);
+  static_cast<void>(vi = i);
+  static_cast<void>(i = vi = 42);
+  (void)(vi = i);
+  (void)(i = vi = 42);
+
+  // Unevaluated operand.
+  decltype(vi = 42) x = vi;
+
+  // Compound assignments.
+  vi += i;
+  vi -= i;
+  vi %= i;
+  vi ^= i;
+  vi |= i;
+  vi /= i;
+  vi = vi += 42;
+  vi += vi = 42;
+  i *= vi;
+  decltype(vi -= 42) x2 = vi;
+
+  // Structured bindings.
+  int a[] = { 10, 5 };
+  const auto & [cxr, cyr] = a;
+  const volatile auto & [cvxr, cvyr] = a;
+  volatile auto & [vxr, vyr] = a;
+}
+
+void
+fn3 ()
+{
+  volatile int i, j, k = 0;
+  i = j = k;
+
+  ACCESS_ONCE(j);
+
+  S s;
+  s.b = 1;
+
+  volatile U u;
+  u.c = 42;
+  i = u.c = 42;
+  u.c += 42;
+
+  volatile T t;
+  t.a = 3;
+  j = t.a = 3;
+  t.a += 3;
+
+  volatile int *src = &i;
+  *src; // No assignment, don't warn.
+}
+
+void
+fn4 ()
+{
+  volatile W vw;
+  W w;
+  // Assignment to objects of a class is defined by the copy/move assignment
+  // operator.
+  vw = w;
+  w = vw;
+}
+
+template<typename T>
+void raccoon ()
+{
+  volatile T t, u;
+  t = 42;
+  u = t = 42;
+  t &= 42;
+}
+
+void
+fn5 ()
+{
+  raccoon<int>();
+}
diff --git gcc/testsuite/g++.dg/expr/bool3.C gcc/testsuite/g++.dg/expr/bool3.C
index 373c202b800..f27399cfc8a 100644
--- gcc/testsuite/g++.dg/expr/bool3.C
+++ gcc/testsuite/g++.dg/expr/bool3.C
@@ -13,8 +13,10 @@ int main()
 
   b++; // { dg-warning "deprecated" "" { target { ! c++17 } } }
   // { dg-error "forbidden" "" { target c++17 } .-1 }
+  // { dg-warning ".volatile.-qualified type is deprecated" "" { target c++2a } .-2 }
   b++; // { dg-warning "deprecated" "" { target { ! c++17 } } }
   // { dg-error "forbidden" "" { target c++17 } .-1 }
+  // { dg-warning ".volatile.-qualified type is deprecated" "" { target c++2a } .-2 }
   i = b;
   if (i != 1)
     abort ();
diff --git gcc/testsuite/g++.dg/expr/bool4.C gcc/testsuite/g++.dg/expr/bool4.C
index dce51ec332e..5891bc311bd 100644
--- gcc/testsuite/g++.dg/expr/bool4.C
+++ gcc/testsuite/g++.dg/expr/bool4.C
@@ -8,6 +8,6 @@ int main()
 {
   my_bool b = false;
   b--; // { dg-error "" }
+  // { dg-warning ".volatile.-qualified type is deprecated" "" { target c++2a } .-1 }
   return 0;
 }
-
diff --git gcc/testsuite/g++.dg/expr/cond9.C gcc/testsuite/g++.dg/expr/cond9.C
index b344c1f683a..f7e092e1445 100644
--- gcc/testsuite/g++.dg/expr/cond9.C
+++ gcc/testsuite/g++.dg/expr/cond9.C
@@ -4,7 +4,7 @@ struct A { // { dg-message "A" }
   A(int);
 };
 
-void foo(volatile A a) { 
+void foo(volatile A a) {  // { dg-warning "deprecated" "" { target c++2a } }
   1 ? a : 0; // { dg-error "qualifiers|lvalue|no match" }
   1 ? 0 : a; // { dg-error "qualifiers|lvalue|no match" }
 } 
diff --git gcc/testsuite/g++.dg/ext/vector25.C gcc/testsuite/g++.dg/ext/vector25.C
index 6c1f5d09878..339865d6942 100644
--- gcc/testsuite/g++.dg/ext/vector25.C
+++ gcc/testsuite/g++.dg/ext/vector25.C
@@ -2,5 +2,5 @@ volatile int i __attribute__((vector_size(8)));
 
 void foo()
 {
-  i += i;
+  i += i; // { dg-warning "deprecated" "" { target c++2a } }
 }
diff --git gcc/testsuite/g++.dg/gomp/depend-iterator-1.C gcc/testsuite/g++.dg/gomp/depend-iterator-1.C
index 6f4aa97ee44..d12670c5159 100644
--- gcc/testsuite/g++.dg/gomp/depend-iterator-1.C
+++ gcc/testsuite/g++.dg/gomp/depend-iterator-1.C
@@ -1,3 +1,5 @@
+// { dg-additional-options "-Wno-volatile" }
+
 int arr[64], arr2[64];
 struct S { int a[4]; } k;
 short arr4[4];
diff --git gcc/testsuite/g++.dg/inherit/covariant21.C gcc/testsuite/g++.dg/inherit/covariant21.C
index 42cdf870081..769cb14ecbc 100644
--- gcc/testsuite/g++.dg/inherit/covariant21.C
+++ gcc/testsuite/g++.dg/inherit/covariant21.C
@@ -6,12 +6,12 @@ struct C : A, B {};
 
 struct X
 {
-  virtual B* foo(volatile int);
+  virtual B* foo(volatile int); // { dg-warning "deprecated" "" { target c++2a } }
 };
 
 struct Y : X
 {
-  virtual C* foo(volatile int);
+  virtual C* foo(volatile int); // { dg-warning "deprecated" "" { target c++2a } }
 };
 
-C* Y::foo(volatile int) { return 0; }
+C* Y::foo(volatile int) { return 0; } // { dg-warning "deprecated" "" { target c++2a } }
diff --git gcc/testsuite/g++.dg/init/ref18.C gcc/testsuite/g++.dg/init/ref18.C
index e704077c26b..81ac76a40d3 100644
--- gcc/testsuite/g++.dg/init/ref18.C
+++ gcc/testsuite/g++.dg/init/ref18.C
@@ -1,6 +1,6 @@
 // PR c++/49395
 
-volatile int foo();
+volatile int foo(); // { dg-warning "deprecated" "" { target c++2a } }
 struct A { volatile int i; };
 typedef volatile int vi;
 
diff --git gcc/testsuite/g++.dg/ipa/pr63838.C gcc/testsuite/g++.dg/ipa/pr63838.C
index d23b3133748..5b6b11d70e5 100644
--- gcc/testsuite/g++.dg/ipa/pr63838.C
+++ gcc/testsuite/g++.dg/ipa/pr63838.C
@@ -7,12 +7,12 @@
 __attribute__((noinline, noclone)) static void bar (int);
 volatile int v;
 void (*fn) ();
-struct S { S () { v++; } ~S () { v++; } };
+struct S { S () { v++; } ~S () { v++; } }; // { dg-warning "deprecated" "" { target c++2a } }
 
 __attribute__((noinline, noclone)) static void
 foo (int x)
 {
-  v++;
+  v++; // { dg-warning "deprecated" "" { target c++2a } }
   if (x == 5)
     bar (x);
 }
@@ -20,7 +20,7 @@ foo (int x)
 __attribute__((noinline, noclone)) static void
 bar (int x)
 {
-  v++;
+  v++; // { dg-warning "deprecated" "" { target c++2a } }
   if (x == 6)
     foo (x);
   else if (x == 5)
diff --git gcc/testsuite/g++.dg/overload/rvalue2.C gcc/testsuite/g++.dg/overload/rvalue2.C
index 8a2290dc293..a829fb5e8cc 100644
--- gcc/testsuite/g++.dg/overload/rvalue2.C
+++ gcc/testsuite/g++.dg/overload/rvalue2.C
@@ -7,5 +7,5 @@ template <class T> void f(const T&);
 int main()
 {
   volatile int i = 0;
-  f(i++);
+  f(i++); // { dg-warning "deprecated" "" { target c++2a } }
 }
diff --git gcc/testsuite/g++.dg/parse/semicolon4.C gcc/testsuite/g++.dg/parse/semicolon4.C
index 5135ec14b1f..bdd1c845187 100644
--- gcc/testsuite/g++.dg/parse/semicolon4.C
+++ gcc/testsuite/g++.dg/parse/semicolon4.C
@@ -25,7 +25,7 @@ struct E1
 } const;			// { dg-error "'const' can only be specified for objects and functions" }
 
 void foo (
-struct E2
+struct E2			// { dg-warning "deprecated" "" { target c++2a } }
 {				// { dg-error "types may not be defined in parameter types" }
   int i;
 } volatile);
diff --git gcc/testsuite/g++.dg/warn/Wreturn-type-4.C gcc/testsuite/g++.dg/warn/Wreturn-type-4.C
index 4f02678e7f9..24a6b41cbd8 100644
--- gcc/testsuite/g++.dg/warn/Wreturn-type-4.C
+++ gcc/testsuite/g++.dg/warn/Wreturn-type-4.C
@@ -3,6 +3,7 @@
 /* { dg-options "-Wignored-qualifiers" } */
 
 volatile void bar(); /* { dg-warning "type qualifiers ignored" } */
+// { dg-warning ".volatile.-qualified return type is deprecated" "" { target c++2a } .-1 }
 
 struct A
 {
diff --git gcc/testsuite/g++.dg/warn/pr36069.C gcc/testsuite/g++.dg/warn/pr36069.C
index efb35c25716..7b166351a4b 100644
--- gcc/testsuite/g++.dg/warn/pr36069.C
+++ gcc/testsuite/g++.dg/warn/pr36069.C
@@ -6,11 +6,13 @@ struct foo {
   bool a;
   volatile bool b,c;  
   foo() { a = b = c = false; } // { dg-bogus "parentheses" }
+  // { dg-warning "deprecated" "" { target c++2a } .-1 }
 };
 
 int main() {
   bool a;
   volatile bool b,c;
   a = b = c = false; // { dg-bogus "parentheses" }
+  // { dg-warning "deprecated" "" { target c++2a } .-1 }
   foo A;
 }
diff --git gcc/testsuite/g++.old-deja/g++.mike/p9506.C gcc/testsuite/g++.old-deja/g++.mike/p9506.C
index db16e3738e2..97594640f96 100644
--- gcc/testsuite/g++.old-deja/g++.mike/p9506.C
+++ gcc/testsuite/g++.old-deja/g++.mike/p9506.C
@@ -3,5 +3,5 @@
 
 char * volatile p;
 void foo() {
-  --p = 0;
+  --p = 0; // { dg-warning "deprecated" "" { target c++2a } }
 }
diff --git gcc/testsuite/g++.old-deja/g++.other/volatile1.C gcc/testsuite/g++.old-deja/g++.other/volatile1.C
index 7d818fbe9e1..a93ef58aa9f 100644
--- gcc/testsuite/g++.old-deja/g++.other/volatile1.C
+++ gcc/testsuite/g++.old-deja/g++.other/volatile1.C
@@ -5,7 +5,7 @@
 class f_class		       // { dg-message "note" "candidates" }
 { };
 
-volatile f_class
+volatile f_class	      // { dg-warning "deprecated" "" { target c++2a } }
 ret_v_f_class()
 {
   f_class t;


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