c++: Implement CWG 2654 - Un-deprecation of compound volatile assignments

--- gcc/cp/typeck.cc.jj	2022-11-09 11:22:42.617628059 +0100
+++ gcc/cp/typeck.cc	2022-11-10 23:19:00.394228067 +0100
@@ -9513,19 +9513,6 @@  cp_build_modify_expr (location_t loc, tr
 			 && 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 and op is not one of the bitwise operators |, &, ^."
-	     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 (modifycode != BIT_AND_EXPR
-	      && modifycode != BIT_IOR_EXPR
-	      && modifycode != BIT_XOR_EXPR
-	      && (TREE_THIS_VOLATILE (lhs) || CP_TYPE_VOLATILE_P (lhstype)))
-	    warning_at (loc, OPT_Wvolatile,
-			"compound 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:
 
--- gcc/testsuite/g++.dg/cpp2a/volatile1.C.jj	2022-08-16 13:15:22.739043862 +0200
+++ gcc/testsuite/g++.dg/cpp2a/volatile1.C	2022-11-10 23:23:18.949717772 +0100
@@ -74,17 +74,17 @@  fn2 ()
   decltype(i = vi = 42) x3 = i;
 
   // Compound assignments.
-  vi += i; // { dg-warning "assignment with .volatile.-qualified left operand is deprecated" "" { target c++20 } }
-  vi -= i; // { dg-warning "assignment with .volatile.-qualified left operand is deprecated" "" { target c++20 } }
-  vi %= i; // { dg-warning "assignment with .volatile.-qualified left operand is deprecated" "" { target c++20 } }
+  vi += i; // { dg-bogus "assignment with .volatile.-qualified left operand is deprecated" }
+  vi -= i; // { dg-bogus "assignment with .volatile.-qualified left operand is deprecated" }
+  vi %= i; // { dg-bogus "assignment with .volatile.-qualified left operand is deprecated" }
   vi ^= i; // { dg-bogus "assignment with .volatile.-qualified left operand is deprecated" }
   vi |= i; // { dg-bogus "assignment with .volatile.-qualified left operand is deprecated" }
   vi &= i; // { dg-bogus "assignment with .volatile.-qualified left operand is deprecated" }
-  vi /= i; // { dg-warning "assignment with .volatile.-qualified left operand is deprecated" "" { target c++20 } }
+  vi /= i; // { dg-bogus "assignment with .volatile.-qualified left operand is deprecated" }
   vi = vi += 42; // { dg-warning "assignment with .volatile.-qualified left operand is deprecated" "" { target c++20 } }
   vi += vi = 42; // { dg-warning "assignment with .volatile.-qualified left operand is deprecated" "" { target c++20 } }
   i *= vi;
-  decltype(vi -= 42) x2 = vi; // { dg-warning "assignment with .volatile.-qualified left operand is deprecated" "" { target c++20 } }
+  decltype(vi -= 42) x2 = vi; // { dg-bogus "assignment with .volatile.-qualified left operand is deprecated" }
 
   // Structured bindings.
   int a[] = { 10, 5 };
@@ -107,12 +107,12 @@  fn3 ()
   volatile U u;
   u.c = 42;
   i = u.c = 42; // { dg-warning "assignment with .volatile.-qualified left operand is deprecated" "" { target c++20 } }
-  u.c += 42; // { dg-warning "assignment with .volatile.-qualified left operand is deprecated" "" { target c++20 } }
+  u.c += 42; // { dg-bogus "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" "" { target c++20 } }
-  t.a += 3; // { dg-warning "assignment with .volatile.-qualified left operand is deprecated" "" { target c++20 } }
+  t.a += 3; // { dg-bogus "assignment with .volatile.-qualified left operand is deprecated" }
 
   volatile int *src = &i;
   *src; // No assignment, don't warn.
@@ -135,7 +135,7 @@  void raccoon ()
   volatile T t, u;
   t = 42;
   u = t = 42; // { dg-warning "assignment with .volatile.-qualified left operand is deprecated" "" { target c++20 } }
-  t += 42; // { dg-warning "assignment with .volatile.-qualified left operand is deprecated" "" { target c++20 } }
+  t += 42; // { dg-bogus "assignment with .volatile.-qualified left operand is deprecated" }
   t &= 42; // { dg-bogus "assignment with .volatile.-qualified left operand is deprecated" }
 }
 
--- gcc/testsuite/g++.dg/cpp2a/volatile3.C.jj	2022-08-16 13:15:22.753043682 +0200
+++ gcc/testsuite/g++.dg/cpp2a/volatile3.C	2022-11-10 23:24:24.781823998 +0100
@@ -75,17 +75,17 @@  fn2 ()
   decltype(i = vi = 42) x3 = i;
 
   // 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-bogus "assignment with .volatile.-qualified left operand is deprecated" }
+  vi -= i; // { dg-bogus "assignment with .volatile.-qualified left operand is deprecated" }
+  vi %= i; // { dg-bogus "assignment with .volatile.-qualified left operand is deprecated" }
   vi ^= i; // { dg-bogus "assignment with .volatile.-qualified left operand is deprecated" }
   vi |= i; // { dg-bogus "assignment with .volatile.-qualified left operand is deprecated" }
   vi &= i; // { dg-bogus "assignment with .volatile.-qualified left operand is deprecated" }
-  vi /= i; // { dg-warning "assignment with .volatile.-qualified left operand is deprecated" }
+  vi /= i; // { dg-bogus "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" }
+  decltype(vi -= 42) x2 = vi; // { dg-bogus "assignment with .volatile.-qualified left operand is deprecated" }
 
   // Structured bindings.
   int a[] = { 10, 5 };
@@ -108,12 +108,12 @@  fn3 ()
   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" }
+  u.c += 42; // { dg-bogus "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" }
+  t.a += 3; // { dg-bogus "assignment with .volatile.-qualified left operand is deprecated" }
 
   volatile int *src = &i;
   *src; // No assignment, don't warn.
@@ -136,7 +136,7 @@  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" }
+  t += 42; // { dg-bogus "assignment with .volatile.-qualified left operand is deprecated" }
   t &= 42; // { dg-bogus "assignment with .volatile.-qualified left operand is deprecated" }
 }
 
--- gcc/testsuite/g++.dg/cpp2a/volatile5.C.jj	2022-08-16 13:15:22.778043359 +0200
+++ gcc/testsuite/g++.dg/cpp2a/volatile5.C	2022-11-10 23:25:07.445244776 +0100
@@ -7,7 +7,7 @@  void
 f (bool b)
 {
   (b ? x : y) = 1;
-  (b ? x : y) += 1; // { dg-warning "compound assignment" "" { target c++20 } }
+  (b ? x : y) += 1; // { dg-bogus "compound assignment" }
   z = (b ? x : y) = 1; // { dg-warning "using value of assignment" "" { target c++20 } }
   ((z = 2) ? x : y) = 1; // { dg-warning "using value of assignment" "" { target c++20 } }
   (b ? (x = 2) : y) = 1; // { dg-warning "using value of assignment" "" { target c++20 } }