c++: Implement P2327R1 - De-deprecating volatile compound operations

From what I can see, this has been voted in as a DR and as it means
we warn less often than before in -std={gnu,c}++2{0,3} modes or with
-Wvolatile, I wonder if it shouldn't be backported to affected release
branches as well.

2022-08-16  Jakub Jelinek  <jakub@redhat.com>

	* typeck.cc (cp_build_modify_expr): Implement
	P2327R1 - De-deprecating volatile compound operations.  Don't warn
	for |=, &= or ^= with volatile lhs.
	* expr.cc (mark_use) <case MODIFY_EXPR>: Adjust warning wording,
	leave out simple.

	* g++.dg/cpp2a/volatile1.C: Adjust for de-deprecation of volatile
	compound |=, &= and ^= operations.
	* g++.dg/cpp2a/volatile3.C: Likewise.
	* g++.dg/cpp2a/volatile5.C: Likewise.

1 files changed, 6 insertions, 2 deletions

diff --git a/gcc/cp/typeck.cc b/gcc/cp/typeck.cc
index 15548e5..6b38c8c 100644
--- a/gcc/cp/typeck.cc
+++ b/gcc/cp/typeck.cc
@@ -9136,10 +9136,14 @@ cp_build_modify_expr (location_t loc, tree lhs, enum tree_code modifycode,
 
 	  /* 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
+	     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 (TREE_THIS_VOLATILE (lhs) || CP_TYPE_VOLATILE_P (lhstype))
+	  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");