Index: gcc/doc/invoke.texi
===================================================================
--- gcc/doc/invoke.texi	(revision 163924)
+++ gcc/doc/invoke.texi	(working copy)
@@ -3053,7 +3053,7 @@ This warning is enabled by @option{-Wall
 
 Suppress warning messages emitted by @code{#warning} directives.
 
-@item -Wdouble-promotion @r{(C and Objective-C only)}
+@item -Wdouble-promotion @r{(C, C++, Objective-C and Objective-C++ only)}
 @opindex Wdouble-promotion
 @opindex Wno-double-promotion
 Give a warning when a value of type @code{float} is implicitly
Index: gcc/c-family/c-common.c
===================================================================
--- gcc/c-family/c-common.c	(revision 163924)
+++ gcc/c-family/c-common.c	(working copy)
@@ -9128,6 +9128,40 @@ warn_for_sign_compare (location_t locati
     }
 }
 
+/* RESULT_TYPE is the result of converting TYPE1 and TYPE2 to a common
+   type via c_common_type.  If -Wdouble-promotion is in use, and the
+   conditions for warning have been met, issue a warning.  GMSGID is
+   the warning message.  It must have two %T specifiers for the type
+   that was converted (generally "float") and the type to which it was
+   converted (generally "double), respectively.  LOC is the location
+   to which the awrning should refer.  */
+
+void
+do_warn_double_promotion (tree result_type, tree type1, tree type2,
+			 const char *gmsgid, location_t loc)
+{
+  tree source_type;
+
+  if (!warn_double_promotion)
+    return;
+  /* If the conversion will not occur at run-time, there is no need to
+     warn about it.  */
+  if (c_inhibit_evaluation_warnings)
+    return;
+  if (TYPE_MAIN_VARIANT (result_type) != double_type_node
+      && TYPE_MAIN_VARIANT (result_type) != complex_double_type_node)
+    return;
+  if (TYPE_MAIN_VARIANT (type1) == float_type_node
+      || TYPE_MAIN_VARIANT (type1) == complex_float_type_node)
+    source_type = type1;
+  else if (TYPE_MAIN_VARIANT (type2) == float_type_node
+	   || TYPE_MAIN_VARIANT (type2) == complex_float_type_node)
+    source_type = type2;
+  else
+    return;
+  warning_at (loc, OPT_Wdouble_promotion, gmsgid, source_type, result_type);
+}
+
 /* Setup a TYPE_DECL node as a typedef representation.
 
    X is a TYPE_DECL for a typedef statement.  Create a brand new
Index: gcc/c-family/c-common.h
===================================================================
--- gcc/c-family/c-common.h	(revision 163924)
+++ gcc/c-family/c-common.h	(working copy)
@@ -900,6 +900,8 @@ extern void warn_for_sign_compare (locat
 				   tree op0, tree op1,
 				   tree result_type,
 				   enum tree_code resultcode);
+extern void do_warn_double_promotion (tree, tree, tree, const char *, 
+				      location_t);
 extern void set_underlying_type (tree x);
 extern VEC(tree,gc) *make_tree_vector (void);
 extern void release_tree_vector (VEC(tree,gc) *);
Index: gcc/testsuite/g++.dg/warn/Wdouble-promotion.C
===================================================================
--- gcc/testsuite/g++.dg/warn/Wdouble-promotion.C	(revision 0)
+++ gcc/testsuite/g++.dg/warn/Wdouble-promotion.C	(revision 0)
@@ -0,0 +1,99 @@
+/* { dg-do compile } */
+/* { dg-options "-Wdouble-promotion" } */
+
+#include <stddef.h>
+
+/* Some targets do not provide <complex.h> so we define I ourselves.  */
+#define I 1.0iF
+#define ID ((_Complex double)I)
+
+float f;
+double d;
+int i;
+long double ld;
+_Complex float cf;
+_Complex double cd;
+_Complex long double cld;
+size_t s;
+
+extern void varargs_fn (int, ...);
+extern void double_fn (double);
+extern float float_fn (void);
+
+void 
+usual_arithmetic_conversions(void) 
+{
+  float local_f;
+  _Complex float local_cf;
+
+  /* Values of type "float" are implicitly converted to "double" or
+     "long double" due to use in arithmetic with "double" or "long
+     double" operands.  */
+  local_f = f + 1.0;         /* { dg-warning "implicit" } */
+  local_f = f - d;           /* { dg-warning "implicit" } */
+  local_f = 1.0f * 1.0;      /* { dg-warning "implicit" } */
+  local_f = 1.0f / d;        /* { dg-warning "implicit" } */
+
+  local_cf = cf + 1.0;       /* { dg-warning "implicit" } */
+  local_cf = cf - d;         /* { dg-warning "implicit" } */
+  local_cf = cf + 1.0 * ID;  /* { dg-warning "implicit" } */
+  local_cf = cf - cd;        /* { dg-warning "implicit" } */
+  
+  local_f = i ? f : d;       /* { dg-warning "implicit" } */
+  i = f == d;                /* { dg-warning "implicit" } */
+  i = d != f;                /* { dg-warning "implicit" } */
+}
+
+void 
+default_argument_promotion (void) 
+{
+  /* Because "f" is part of the variable argument list, it is promoted
+     to "double".  */
+  varargs_fn (1, f);   /* { dg-warning "implicit" } */
+}
+
+/* There is no warning when an explicit cast is used to perform the
+   conversion.  */
+
+void
+casts (void) 
+{
+  float local_f;
+  _Complex float local_cf;
+
+  local_f = (double)f + 1.0;                 /* { dg-bogus "implicit" } */
+  local_f = (double)f - d;                   /* { dg-bogus "implicit" } */
+  local_f = (double)1.0f + 1.0;              /* { dg-bogus "implicit" } */
+  local_f = (double)1.0f - d;                /* { dg-bogus "implicit" } */
+
+  local_cf = (_Complex double)cf + 1.0;      /* { dg-bogus "implicit" } */
+  local_cf = (_Complex double)cf - d;        /* { dg-bogus "implicit" } */
+  local_cf = (_Complex double)cf + 1.0 * ID; /* { dg-bogus "implicit" } */
+  local_cf = (_Complex double)cf - cd;       /* { dg-bogus "implicit" } */
+
+  local_f = i ? (double)f : d;               /* { dg-bogus "implicit" } */
+  i = (double)f == d;                        /* { dg-bogus "implicit" } */
+  i = d != (double)f;                        /* { dg-bogus "implicit" } */
+}
+
+/* There is no warning on conversions that occur in assignment (and
+   assignment-like) contexts.  */
+
+void 
+assignments (void)
+{
+  d = f;           /* { dg-bogus "implicit" } */
+  double_fn (f);   /* { dg-bogus "implicit" } */
+  d = float_fn (); /* { dg-bogus "implicit" } */
+}
+
+/* There is no warning in non-evaluated contexts.  */
+
+void
+non_evaluated (void)
+{
+  s = sizeof (f + 1.0);             /* { dg-bogus "implicit" } */
+  s = __alignof__ (f + 1.0);        /* { dg-bogus "implicit" } */
+  d = (__typeof__(f + 1.0))f;       /* { dg-bogus "implicit" } */
+  s = sizeof (i ? f : d);           /* { dg-bogus "implicit" } */
+}
Index: gcc/cp/typeck.c
===================================================================
--- gcc/cp/typeck.c	(revision 163924)
+++ gcc/cp/typeck.c	(working copy)
@@ -265,6 +265,7 @@ cp_common_type (tree t1, tree t2)
   enum tree_code code2 = TREE_CODE (t2);
   tree attributes;
 
+
   /* In what follows, we slightly generalize the rules given in [expr] so
      as to deal with `long long' and `complex'.  First, merge the
      attributes.  */
@@ -4362,7 +4363,14 @@ cp_build_binary_op (location_t location,
   if (!result_type
       && arithmetic_types_p
       && (shorten || common || short_compare))
-    result_type = cp_common_type (type0, type1);
+    {
+      result_type = cp_common_type (type0, type1);
+      do_warn_double_promotion (result_type, type0, type1,
+				"implicit conversion from %qT to %qT "
+				"to match other operand of binary "
+				"expression",
+				location);
+    }
 
   if (!result_type)
     {
Index: gcc/cp/call.c
===================================================================
--- gcc/cp/call.c	(revision 163924)
+++ gcc/cp/call.c	(working copy)
@@ -4009,6 +4009,10 @@ build_conditional_expr (tree arg1, tree 
       /* In this case, there is always a common type.  */
       result_type = type_after_usual_arithmetic_conversions (arg2_type,
 							     arg3_type);
+      do_warn_double_promotion (result_type, arg2_type, arg3_type,
+				"implicit conversion from %qT to %qT to "
+				"match other result of conditional",
+				input_location);
 
       if (TREE_CODE (arg2_type) == ENUMERAL_TYPE
 	  && TREE_CODE (arg3_type) == ENUMERAL_TYPE)
@@ -5301,11 +5305,14 @@ convert_like_real (conversion *convs, tr
 tree
 convert_arg_to_ellipsis (tree arg)
 {
+  tree arg_type;
+
   /* [expr.call]
 
      The lvalue-to-rvalue, array-to-pointer, and function-to-pointer
      standard conversions are performed.  */
   arg = decay_conversion (arg);
+  arg_type = TREE_TYPE (arg);
   /* [expr.call]
 
      If the argument has integral or enumeration type that is subject
@@ -5313,21 +5320,29 @@ convert_arg_to_ellipsis (tree arg)
      type that is subject to the floating point promotion
      (_conv.fpprom_), the value of the argument is converted to the
      promoted type before the call.  */
-  if (TREE_CODE (TREE_TYPE (arg)) == REAL_TYPE
-      && (TYPE_PRECISION (TREE_TYPE (arg))
+  if (TREE_CODE (arg_type) == REAL_TYPE
+      && (TYPE_PRECISION (arg_type)
 	  < TYPE_PRECISION (double_type_node))
-      && !DECIMAL_FLOAT_MODE_P (TYPE_MODE (TREE_TYPE (arg))))
-    arg = convert_to_real (double_type_node, arg);
-  else if (NULLPTR_TYPE_P (TREE_TYPE (arg)))
+      && !DECIMAL_FLOAT_MODE_P (TYPE_MODE (arg_type)))
+    {
+      if (warn_double_promotion && !c_inhibit_evaluation_warnings)
+	warning (OPT_Wdouble_promotion,
+		 "implicit conversion from %qT to %qT when passing "
+		 "argument to function",
+		 arg_type, double_type_node);
+      arg = convert_to_real (double_type_node, arg);
+    }
+  else if (NULLPTR_TYPE_P (arg_type))
     arg = null_pointer_node;
-  else if (INTEGRAL_OR_ENUMERATION_TYPE_P (TREE_TYPE (arg)))
+  else if (INTEGRAL_OR_ENUMERATION_TYPE_P (arg_type))
     arg = perform_integral_promotions (arg);
 
   arg = require_complete_type (arg);
+  arg_type = TREE_TYPE (arg);
 
   if (arg != error_mark_node
-      && (type_has_nontrivial_copy_init (TREE_TYPE (arg))
-	  || TYPE_HAS_NONTRIVIAL_DESTRUCTOR (TREE_TYPE (arg))))
+      && (type_has_nontrivial_copy_init (arg_type)
+	  || TYPE_HAS_NONTRIVIAL_DESTRUCTOR (arg_type)))
     {
       /* [expr.call] 5.2.2/7:
 	 Passing a potentially-evaluated argument of class type (Clause 9)
@@ -5342,7 +5357,7 @@ convert_arg_to_ellipsis (tree arg)
 	 it is not potentially-evaluated.  */
       if (cp_unevaluated_operand == 0)
 	error ("cannot pass objects of non-trivially-copyable "
-	       "type %q#T through %<...%>", TREE_TYPE (arg));
+	       "type %q#T through %<...%>", arg_type);
     }
 
   return arg;
Index: gcc/c-typeck.c
===================================================================
--- gcc/c-typeck.c	(revision 163924)
+++ gcc/c-typeck.c	(working copy)
@@ -4036,40 +4036,6 @@ ep_convert_and_check (tree type, tree ex
   return convert (type, expr);
 }
 
-/* RESULT_TYPE is the result of converting TYPE1 and TYPE2 to a common
-   type via c_common_type.  If -Wdouble-promotion is in use, and the
-   conditions for warning have been met, issue a warning.  GMSGID is
-   the warning message.  It must have two %T specifiers for the type
-   that was converted (generally "float") and the type to which it was
-   converted (generally "double), respectively.  LOC is the location
-   to which the awrning should refer.  */
-
-static void
-do_warn_double_promotion (tree result_type, tree type1, tree type2,
-			 const char *gmsgid, location_t loc)
-{
-  tree source_type;
-
-  if (!warn_double_promotion)
-    return;
-  /* If the conversion will not occur at run-time, there is no need to
-     warn about it.  */
-  if (c_inhibit_evaluation_warnings)
-    return;
-  if (TYPE_MAIN_VARIANT (result_type) != double_type_node
-      && TYPE_MAIN_VARIANT (result_type) != complex_double_type_node)
-    return;
-  if (TYPE_MAIN_VARIANT (type1) == float_type_node
-      || TYPE_MAIN_VARIANT (type1) == complex_float_type_node)
-    source_type = type1;
-  else if (TYPE_MAIN_VARIANT (type2) == float_type_node
-	   || TYPE_MAIN_VARIANT (type2) == complex_float_type_node)
-    source_type = type2;
-  else
-    return;
-  warning_at (loc, OPT_Wdouble_promotion, gmsgid, source_type, result_type);
-}
-
 /* Build and return a conditional expression IFEXP ? OP1 : OP2.  If
    IFEXP_BCP then the condition is a call to __builtin_constant_p, and
    if folded to an integer constant then the unselected half may
