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


On 8/26/19 1:46 PM, Marek Polacek wrote:
On Fri, Aug 23, 2019 at 07:39:57PM -0400, Marek Polacek wrote:
On Fri, Aug 23, 2019 at 02:43:42PM -0700, Jason Merrill wrote:
On 8/23/19 9:32 AM, Marek Polacek wrote:
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.

It wouldn't work to warn in mark_[lr]value_use?

My worry is that we might be calling those too often and generate redundant
diagnostics but I'll have to play with that a bit before I can say for sure.

So indeed we call mark_use multiple times on the same expr, but that is not an
unsurmountable problem, I just need to use TREE_THIS_VOLATILE to prevent that.
FWIW, using TREE_NO_WARNING didn't work for

   &(vi = i);

because finish_parenthesized_expr sets TREE_NO_WARNING and so we wouldn't warn
at all.  But warning in mark_use did simplify things a bit, thanks for the
suggestion.

One nit is that we emit two warnings for

   vi = vi += 10;

which could be fixed but I'm not entirely sure it's even worth it.

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

2019-08-26  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_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_use) <case MODIFY_EXPR>: Emit a -Wvolatile warning.
	* 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.  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.

Maybe "deprecated uses"?

+
  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..49fa47ac3af 100644
--- gcc/cp/cp-gimplify.c
+++ gcc/cp/cp-gimplify.c
@@ -2507,6 +2507,9 @@ 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 9f7923871db..de312c47c21 100644
--- gcc/cp/decl.c
+++ gcc/cp/decl.c
@@ -11189,6 +11189,10 @@ 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:
@@ -11579,6 +11583,13 @@ 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;
@@ -13320,6 +13331,13 @@ 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..bb5097c988d 100644
--- gcc/cp/expr.c
+++ gcc/cp/expr.c
@@ -207,6 +207,27 @@ mark_use (tree expr, bool rvalue_p, bool read_p,
        recurse_op[0] = true;
        break;
+ case MODIFY_EXPR:
+	{
+	  tree lhs = TREE_OPERAND (expr, 0);
+	  /* [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 (read_p
+	      && (TREE_THIS_VOLATILE (lhs)
+		  || CP_TYPE_VOLATILE_P (TREE_TYPE (lhs)))
+	      && !TREE_THIS_VOLATILE (expr))
+	    {
+	      warning_at (location_of (expr), OPT_Wvolatile,
+			  "assignment with %<volatile%>-qualified left "
+			  "operand is deprecated");

This should be more specific; the assignment itself isn't deprecated, but rather using the assignment as an lvalue or rvalue.

+	      /* Make sure not to warn about this assignment again.  */
+	      TREE_THIS_VOLATILE (expr) = true;
+	    }
+	  break;
+	}
+
      default:
        break;
      }
diff --git gcc/cp/typeck.c gcc/cp/typeck.c
index e2a4f285a72..0acdf4e3426 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)
  	  {
@@ -8278,6 +8289,15 @@ 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");

And this should say "compound assignment ..."

  	  /* Preevaluate the RHS to make sure its evaluation is complete
  	     before the lvalue-to-rvalue conversion of the LHS:
@@ -8450,8 +8470,8 @@ 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;
    if (!plain_assign)
diff --git gcc/doc/invoke.texi gcc/doc/invoke.texi
index 549e043c67c..0ea2ae284ca 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

This should also be more specific.

, 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;

I guess we should also test that there's no warning for

decltype(i = vi = 42)

since this is also an unevaluated context. It's a bit odd the proposal uses "unevaluated context" rather than "unevaluated operand".

+
+  // 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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