Fix conversions for built-in operator overloading candidates.

While working on C++20 operator<=>, I noticed that build_new_op_1 was doing
too much conversion when a built-in candidate was selected; the standard
says it should only perform user-defined conversions, and then leave the
normal operator semantics to handle any standard conversions.  This is
important for operator<=> because a comparison of two different unscoped
enums is ill-formed; if we promote the enums to int here, cp_build_binary_op
never gets to see the original operand types, so we can't give the error.

I'm also disabling -Wmaybe-uninitialized for expmed.c to avoid the bootstrap
failure from the last time I applied this patch.

	* call.c (build_new_op_1): Don't apply any standard conversions to
	the operands of a built-in operator.  Don't suppress conversions in
	cp_build_unary_op.
	* typeck.c (cp_build_unary_op): Do integral promotions for enums.

	PR tree-optimization/91825
	* expmed.c: Reduce -Wmaybe-uninitialized to warning.

From-SVN: r277864

gcc/ChangeLog

+2019-10-26  Jason Merrill  <jason@redhat.com>
+
+	PR tree-optimization/91825
+	* expmed.c: Reduce -Wmaybe-uninitialized to warning.
+
 2019-11-05  Jim Wilson  <jimw@sifive.com>
 
 	PR middle-end/92263

gcc/cp/ChangeLog

+2019-09-15  Jason Merrill  <jason@redhat.com>
+
+	* call.c (build_new_op_1): Don't apply any standard conversions to
+	the operands of a built-in operator.  Don't suppress conversions in
+	cp_build_unary_op.
+	* typeck.c (cp_build_unary_op): Do integral promotions for enums.
+
 2019-11-04  Jason Merrill  <jason@redhat.com>
 
 	Use vec instead of raw array for built-in candidates.

gcc/cp/call.c

@@ -6156,41 +6156,40 @@ build_new_op_1 (const op_location_t &loc, enum tree_code code, int flags,
 	      break;
 	    }
 
-	  /* We need to strip any leading REF_BIND so that bitfields
-	     don't cause errors.  This should not remove any important
-	     conversions, because builtins don't apply to class
-	     objects directly.  */
+	  /* "If a built-in candidate is selected by overload resolution, the
+	     operands of class type are converted to the types of the
+	     corresponding parameters of the selected operation function,
+	     except that the second standard conversion sequence of a
+	     user-defined conversion sequence (12.3.3.1.2) is not applied."  */
 	  conv = cand->convs[0];
-	  if (conv->kind == ck_ref_bind)
-	    conv = next_conversion (conv);
-	  arg1 = convert_like (conv, arg1, complain);
+	  if (conv->user_conv_p)
+	    {
+	      while (conv->kind != ck_user)
+		conv = next_conversion (conv);
+	      arg1 = convert_like (conv, arg1, complain);
+	    }
 
 	  if (arg2)
 	    {
 	      conv = cand->convs[1];
-	      if (conv->kind == ck_ref_bind)
-		conv = next_conversion (conv);
-	      else
-		arg2 = decay_conversion (arg2, complain);
-
-	      /* We need to call warn_logical_operator before
-		 converting arg2 to a boolean_type, but after
-		 decaying an enumerator to its value.  */
-	      if (complain & tf_warning)
-		warn_logical_operator (loc, code, boolean_type_node,
-				       code_orig_arg1, arg1,
-				       code_orig_arg2, arg2);
-
-	      arg2 = convert_like (conv, arg2, complain);
+	      if (conv->user_conv_p)
+		{
+		  while (conv->kind != ck_user)
+		    conv = next_conversion (conv);
+		  arg2 = convert_like (conv, arg2, complain);
+		}
 	    }
+
 	  if (arg3)
 	    {
 	      conv = cand->convs[2];
-	      if (conv->kind == ck_ref_bind)
-		conv = next_conversion (conv);
-	      convert_like (conv, arg3, complain);
+	      if (conv->user_conv_p)
+		{
+		  while (conv->kind != ck_user)
+		    conv = next_conversion (conv);
+		  arg3 = convert_like (conv, arg3, complain);
+		}
 	    }
-
 	}
     }
 
@@ -6258,7 +6257,7 @@ build_new_op_1 (const op_location_t &loc, enum tree_code code, int flags,
     case REALPART_EXPR:
     case IMAGPART_EXPR:
     case ABS_EXPR:
-      return cp_build_unary_op (code, arg1, candidates != 0, complain);
+      return cp_build_unary_op (code, arg1, false, complain);
 
     case ARRAY_REF:
       return cp_build_array_ref (input_location, arg1, arg2, complain);

gcc/cp/typeck.c

@@ -6298,7 +6298,7 @@ cp_build_unary_op (enum tree_code code, tree xarg, bool noconvert,
 		       : _("wrong type argument to unary plus"));
 	else
 	  {
-	    if (!noconvert && CP_INTEGRAL_TYPE_P (TREE_TYPE (arg)))
+	    if (!noconvert && INTEGRAL_OR_ENUMERATION_TYPE_P (TREE_TYPE (arg)))
 	      arg = cp_perform_integral_promotions (arg, complain);
 
 	    /* Make sure the result is not an lvalue: a unary plus or minus
@@ -6323,7 +6323,7 @@ cp_build_unary_op (enum tree_code code, tree xarg, bool noconvert,
 						   | WANT_VECTOR_OR_COMPLEX,
 						   arg, true)))
 	errstring = _("wrong type argument to bit-complement");
-      else if (!noconvert && CP_INTEGRAL_TYPE_P (TREE_TYPE (arg)))
+      else if (!noconvert && INTEGRAL_OR_ENUMERATION_TYPE_P (TREE_TYPE (arg)))
 	{
 	  /* Warn if the expression has boolean value.  */
 	  if (TREE_CODE (TREE_TYPE (arg)) == BOOLEAN_TYPE

gcc/expmed.c

@@ -18,6 +18,8 @@ You should have received a copy of the GNU General Public License
 along with GCC; see the file COPYING3.  If not see
 <http://www.gnu.org/licenses/>.  */
 
+/* Work around tree-optimization/91825.  */
+#pragma GCC diagnostic warning "-Wmaybe-uninitialized"
 
 #include "config.h"
 #include "system.h"