Index: lib/Sema/SemaExpr.cpp
===================================================================
--- lib/Sema/SemaExpr.cpp
+++ lib/Sema/SemaExpr.cpp
@@ -15409,7 +15409,10 @@
 
 ExprResult Sema::CheckBooleanCondition(SourceLocation Loc, Expr *E,
                                        bool IsConstexpr) {
-  DiagnoseAssignmentAsCondition(E);
+  // an assignment always produces an lvalue, and we now check this inside
+  // PerformImplicitConversion, as conditions will always be implicitly
+  // converted to an rvalue
+  // DiagnoseAssignmentAsCondition(E);
   if (ParenExpr *parenE = dyn_cast<ParenExpr>(E))
     DiagnoseEqualityWithExtraParens(parenE);
 
Index: lib/Sema/SemaExprCXX.cpp
===================================================================
--- lib/Sema/SemaExprCXX.cpp
+++ lib/Sema/SemaExprCXX.cpp
@@ -3839,6 +3839,11 @@
     FromType = From->getType();
   }
 
+  // implicit boolean conversions should have their assignments checked
+  if (SCS.Second == ICK_Boolean_Conversion || FromType == Context.BoolTy) {
+    DiagnoseAssignmentAsCondition(From->IgnoreImpCasts());
+  }
+
   // If we're converting to an atomic type, first convert to the corresponding
   // non-atomic type.
   QualType ToAtomicType;