diff --git a/gcc/cp/semantics.cc b/gcc/cp/semantics.cc
index 0f7f4e87ae4..b57c1ac868b 100644
--- a/gcc/cp/semantics.cc
+++ b/gcc/cp/semantics.cc
@@ -881,13 +881,17 @@ maybe_convert_cond (tree cond)
   /* Do the conversion.  */
   cond = convert_from_reference (cond);
 
-  if ((TREE_CODE (cond) == MODIFY_EXPR || is_assignment_op_expr_p (cond))
+  tree inner = REFERENCE_REF_P (cond) ? TREE_OPERAND (cond, 0) : cond;
+  if ((TREE_CODE (inner) == MODIFY_EXPR
+       || (TREE_CODE (inner) == MODOP_EXPR
+	   && TREE_CODE (TREE_OPERAND (inner, 1)) == NOP_EXPR)
+       || is_assignment_op_expr_p (inner))
       && warn_parentheses
-      && !warning_suppressed_p (cond, OPT_Wparentheses)
-      && warning_at (cp_expr_loc_or_input_loc (cond),
+      && !warning_suppressed_p (inner, OPT_Wparentheses)
+      && warning_at (cp_expr_loc_or_input_loc (inner),
 		     OPT_Wparentheses, "suggest parentheses around "
 				       "assignment used as truth value"))
-    suppress_warning (cond, OPT_Wparentheses);
+    suppress_warning (inner, OPT_Wparentheses);
 
   return condition_conversion (cond);
 }
@@ -2155,8 +2159,11 @@ cp_expr
 finish_parenthesized_expr (cp_expr expr)
 {
   if (EXPR_P (expr))
+    {
+      tree inner = REFERENCE_REF_P (expr) ? TREE_OPERAND (expr, 0) : *expr;
       /* This inhibits warnings in c_common_truthvalue_conversion.  */
-    suppress_warning (expr, OPT_Wparentheses);
+      suppress_warning (inner, OPT_Wparentheses);
+    }
 
   if (TREE_CODE (expr) == OFFSET_REF
       || TREE_CODE (expr) == SCOPE_REF)
diff --git a/gcc/cp/typeck.cc b/gcc/cp/typeck.cc
index 459739d5866..74f5fced060 100644
--- a/gcc/cp/typeck.cc
+++ b/gcc/cp/typeck.cc
@@ -9721,13 +9721,13 @@ build_x_modify_expr (location_t loc, tree lhs, enum tree_code modifycode,
   if (lhs == error_mark_node || rhs == error_mark_node)
     return cp_expr (error_mark_node, loc);
 
+  tree op = build_min (modifycode, void_type_node, NULL_TREE, NULL_TREE);
+
   if (processing_template_decl)
     {
-      if (modifycode == NOP_EXPR
-	  || type_dependent_expression_p (lhs)
+      if (type_dependent_expression_p (lhs)
 	  || type_dependent_expression_p (rhs))
 	{
-	  tree op = build_min_nt_loc (loc, modifycode, NULL_TREE, NULL_TREE);
 	  tree rval = build_min_nt_loc (loc, MODOP_EXPR, lhs, op, rhs);
 	  if (modifycode != NOP_EXPR)
 	    TREE_TYPE (rval)
@@ -9739,15 +9739,15 @@ build_x_modify_expr (location_t loc, tree lhs, enum tree_code modifycode,
       rhs = build_non_dependent_expr (rhs);
     }
 
-  if (modifycode != NOP_EXPR)
-    {
-      tree op = build_nt (modifycode, NULL_TREE, NULL_TREE);
-      tree rval = build_new_op (loc, MODIFY_EXPR, LOOKUP_NORMAL,
+  tree rval;
+  if (modifycode == NOP_EXPR)
+    rval = cp_build_modify_expr (loc, lhs, modifycode, rhs, complain);
+  else
+    rval = build_new_op (loc, MODIFY_EXPR, LOOKUP_NORMAL,
 			 lhs, rhs, op, lookups, &overload, complain);
-      if (rval)
-	{
   if (rval == error_mark_node)
-	    return rval;
+    return error_mark_node;
+  if (modifycode != NOP_EXPR)
     suppress_warning (rval /* What warning? */);
   if (processing_template_decl)
     {
@@ -9760,9 +9760,6 @@ build_x_modify_expr (location_t loc, tree lhs, enum tree_code modifycode,
     }
   return rval;
 }
-    }
-  return cp_build_modify_expr (loc, lhs, modifycode, rhs, complain);
-}
 
 /* Helper function for get_delta_difference which assumes FROM is a base
    class of TO.  Returns a delta for the conversion of pointer-to-member
diff --git a/gcc/testsuite/g++.dg/cpp0x/static_assert15.C b/gcc/testsuite/g++.dg/cpp0x/static_assert15.C
index a740f73fd4a..d5f50d07c91 100644
--- a/gcc/testsuite/g++.dg/cpp0x/static_assert15.C
+++ b/gcc/testsuite/g++.dg/cpp0x/static_assert15.C
@@ -5,6 +5,6 @@ template<int x>
 struct a {
   constexpr void b() {
     int c;
-    static_assert(c %= 1, "");
+    static_assert(c %= 1, ""); // { dg-error "constant" }
   }
 };
diff --git a/gcc/testsuite/g++.dg/expr/unary2.C b/gcc/testsuite/g++.dg/expr/unary2.C
index 5962bfe19c9..4db68375944 100644
--- a/gcc/testsuite/g++.dg/expr/unary2.C
+++ b/gcc/testsuite/g++.dg/expr/unary2.C
@@ -1,9 +1,7 @@
+// PR c++/18474
 // { dg-do compile }
 // Unary plus/minus are not lvalues.
 
-// In templates we require an instantiation to emit the diagnostic. This
-//  is wrong and it is PR 18474.
-
 int n;
 
 void f(void)
@@ -15,6 +13,6 @@ void f(void)
 template <int>
 void g(void)
 {
-  -n = 0;        // { dg-error "lvalue" "" { xfail *-*-* } }
-  +n = 0;        // { dg-error "lvalue" "" { xfail *-*-* } }
+  -n = 0;        // { dg-error "lvalue" "" }
+  +n = 0;        // { dg-error "lvalue" "" }
 }
diff --git a/gcc/testsuite/g++.dg/template/init7.C b/gcc/testsuite/g++.dg/template/init7.C
index bb26c8f92b5..94fc22f578c 100644
--- a/gcc/testsuite/g++.dg/template/init7.C
+++ b/gcc/testsuite/g++.dg/template/init7.C
@@ -6,4 +6,4 @@ template<typename> struct A
   static const int i=0;
 };
 
-template<typename T> const int A<T>::i = 0=0; /* { dg-error "duplicate initialization" } */
+template<typename T> const int A<T>::i = T()=0; /* { dg-error "duplicate initialization" } */
diff --git a/gcc/testsuite/g++.dg/template/non-dependent26.C b/gcc/testsuite/g++.dg/template/non-dependent26.C
new file mode 100644
index 00000000000..1faa39a4b1a
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/non-dependent26.C
@@ -0,0 +1,25 @@
+// Verify non-dependent assignment expressions are recognized as such
+// and are checked ahead of time.
+// PR c++/63198
+// { dg-do compile { target c++11 } }
+
+struct X { using t1 = int; };
+struct Y { X operator=(const Y&); } y;
+template<class T> void f1(decltype(y = y)::t1);
+
+int n;
+template<class T> void f2(decltype(n = n)::t1); // { dg-error "not a class" }
+template<class T> void f3(decltype(n += n)::t1); // { dg-error "not a class" }
+
+template<class T>
+void g() {
+  const int n;
+  n = 42; // { dg-error "read-only" }
+
+  const X x;
+  x = {}; // { dg-error "no match" }
+
+  const Y y;
+  y = {}; // { dg-error "no match" }
+  Y{} = X{}; // { dg-error "no match" }
+}
diff --git a/gcc/testsuite/g++.dg/template/recurse3.C b/gcc/testsuite/g++.dg/template/recurse3.C
index f1db7c5cbca..70c6152d063 100644
--- a/gcc/testsuite/g++.dg/template/recurse3.C
+++ b/gcc/testsuite/g++.dg/template/recurse3.C
@@ -1,14 +1,14 @@
 // PR c++/44609
 // { dg-options -ftemplate-depth=10 }
 
-template<int N>
+template<class T, int N>
 void f()
 {
-  0 = 0;			// { dg-error "lvalue required" }
-  f<N+1>();			// { dg-bogus "instantiation depth" }
+  T(0) = 0;			// { dg-error "lvalue required" }
+  f<T, N+1>();			// { dg-bogus "instantiation depth" }
 }
 
 int main()
 {
-  f<0>();
+  f<int, 0>();
 }
diff --git a/gcc/testsuite/g++.dg/warn/Wparentheses-32.C b/gcc/testsuite/g++.dg/warn/Wparentheses-32.C
new file mode 100644
index 00000000000..719a9d9e73a
--- /dev/null
+++ b/gcc/testsuite/g++.dg/warn/Wparentheses-32.C
@@ -0,0 +1,28 @@
+// Verify we issue -Wparentheses warnings at template definition time
+// (for suitable non-dependent expressions).
+// { dg-additional-options "-Wparentheses" }
+
+struct X { operator bool(); };
+struct Y { Y& operator=(const Y&); operator bool(); };
+struct Z { int m; operator bool(); };
+
+template<class T>
+void f() {
+  int n, m;
+  if (n = m) { } // { dg-warning "parentheses" }
+
+  X x1, x2;
+  if (x1 = x2) { } // { dg-warning "parentheses" }
+
+  Y y1, y2;
+  if (y1 = y2) { } // { dg-warning "parentheses" }
+
+  Z z1, z2;
+  if (z1 = z2) { } // { dg-warning "parentheses" }
+
+  bool b;
+  b = m = n; // { dg-warning "parentheses" "" { xfail *-*-* } }
+  b = x1 = x2; // { dg-warning "parentheses" "" { xfail *-*-* } }
+  b = y1 = y2; // { dg-warning "parentheses" "" { xfail *-*-* } }
+  b = z1 = z2; // { dg-warning "parentheses" "" { xfail *-*-* } }
+}
diff --git a/libstdc++-v3/testsuite/26_numerics/random/discard_block_engine/cons/seed_seq2.cc b/libstdc++-v3/testsuite/26_numerics/random/discard_block_engine/cons/seed_seq2.cc
index 720ce96dc28..0d7e667382d 100644
--- a/libstdc++-v3/testsuite/26_numerics/random/discard_block_engine/cons/seed_seq2.cc
+++ b/libstdc++-v3/testsuite/26_numerics/random/discard_block_engine/cons/seed_seq2.cc
@@ -51,7 +51,7 @@ struct seed_seq
   // T is convertible to the engine's result_type:
   operator T() const noexcept { return T(); }
 
-  bool called = false;
+  mutable bool called = false;
 };
 
 using engine_type
diff --git a/libstdc++-v3/testsuite/26_numerics/random/independent_bits_engine/cons/seed_seq2.cc b/libstdc++-v3/testsuite/26_numerics/random/independent_bits_engine/cons/seed_seq2.cc
index f378621805f..2ef563038cc 100644
--- a/libstdc++-v3/testsuite/26_numerics/random/independent_bits_engine/cons/seed_seq2.cc
+++ b/libstdc++-v3/testsuite/26_numerics/random/independent_bits_engine/cons/seed_seq2.cc
@@ -51,7 +51,7 @@ struct seed_seq
   // T is convertible to the engine's result_type:
   operator T() const noexcept { return T(); }
 
-  bool called = false;
+  mutable bool called = false;
 };
 
 using engine_type
diff --git a/libstdc++-v3/testsuite/26_numerics/random/linear_congruential_engine/cons/seed_seq2.cc b/libstdc++-v3/testsuite/26_numerics/random/linear_congruential_engine/cons/seed_seq2.cc
index c1cfe9da7fb..071ed75d8d8 100644
--- a/libstdc++-v3/testsuite/26_numerics/random/linear_congruential_engine/cons/seed_seq2.cc
+++ b/libstdc++-v3/testsuite/26_numerics/random/linear_congruential_engine/cons/seed_seq2.cc
@@ -51,7 +51,7 @@ struct seed_seq
   // T is convertible to the engine's result_type:
   operator T() const noexcept { return T(); }
 
-  bool called = false;
+  mutable bool called = false;
 };
 
 using engine_type
diff --git a/libstdc++-v3/testsuite/26_numerics/random/mersenne_twister_engine/cons/seed_seq2.cc b/libstdc++-v3/testsuite/26_numerics/random/mersenne_twister_engine/cons/seed_seq2.cc
index 52476026533..2fb9622fda0 100644
--- a/libstdc++-v3/testsuite/26_numerics/random/mersenne_twister_engine/cons/seed_seq2.cc
+++ b/libstdc++-v3/testsuite/26_numerics/random/mersenne_twister_engine/cons/seed_seq2.cc
@@ -51,7 +51,7 @@ struct seed_seq
   // T is convertible to the engine's result_type:
   operator T() const noexcept { return T(); }
 
-  bool called = false;
+  mutable bool called = false;
 };
 
 using engine_type
diff --git a/libstdc++-v3/testsuite/26_numerics/random/shuffle_order_engine/cons/seed_seq2.cc b/libstdc++-v3/testsuite/26_numerics/random/shuffle_order_engine/cons/seed_seq2.cc
index 1ca783e3044..3fa9c9ad8d3 100644
--- a/libstdc++-v3/testsuite/26_numerics/random/shuffle_order_engine/cons/seed_seq2.cc
+++ b/libstdc++-v3/testsuite/26_numerics/random/shuffle_order_engine/cons/seed_seq2.cc
@@ -51,7 +51,7 @@ struct seed_seq
   // T is convertible to the engine's result_type:
   operator T() const noexcept { return T(); }
 
-  bool called = false;
+  mutable bool called = false;
 };
 
 using engine_type
diff --git a/libstdc++-v3/testsuite/26_numerics/random/subtract_with_carry_engine/cons/seed_seq2.cc b/libstdc++-v3/testsuite/26_numerics/random/subtract_with_carry_engine/cons/seed_seq2.cc
index 08beb3bcf93..25d19a0ba66 100644
--- a/libstdc++-v3/testsuite/26_numerics/random/subtract_with_carry_engine/cons/seed_seq2.cc
+++ b/libstdc++-v3/testsuite/26_numerics/random/subtract_with_carry_engine/cons/seed_seq2.cc
@@ -51,7 +51,7 @@ struct seed_seq
   // T is convertible to the engine's result_type:
   operator T() const noexcept { return T(); }
 
-  bool called = false;
+  mutable bool called = false;
 };
 
 using engine_type
diff --git a/libstdc++-v3/testsuite/ext/random/simd_fast_mersenne_twister_engine/cons/seed_seq2.cc b/libstdc++-v3/testsuite/ext/random/simd_fast_mersenne_twister_engine/cons/seed_seq2.cc
index b629053585e..fe798f2f05b 100644
--- a/libstdc++-v3/testsuite/ext/random/simd_fast_mersenne_twister_engine/cons/seed_seq2.cc
+++ b/libstdc++-v3/testsuite/ext/random/simd_fast_mersenne_twister_engine/cons/seed_seq2.cc
@@ -52,7 +52,7 @@ struct seed_seq
   // T is convertible to the engine's result_type:
   operator T() const noexcept { return T(); }
 
-  bool called = false;
+  mutable bool called = false;
 };
 
 using engine_type
