[C++] PR 63265

Index: c/c-typeck.c
===================================================================
--- c/c-typeck.c	(revision 217282)
+++ c/c-typeck.c	(working copy)
@@ -10545,7 +10545,8 @@  build_binary_op (location_t location, enum tree_co
 		{
 		  int_const = false;
 		  if (c_inhibit_evaluation_warnings == 0)
-		    warning_at (location, 0, "left shift count is negative");
+		    warning_at (location, OPT_Wshift_count_negative,
+				"left shift count is negative");
 		}
 
 	      else if (compare_tree_int (op1, TYPE_PRECISION (type0)) >= 0)
@@ -10552,8 +10553,8 @@  build_binary_op (location_t location, enum tree_co
 		{
 		  int_const = false;
 		  if (c_inhibit_evaluation_warnings == 0)
-		    warning_at (location, 0, "left shift count >= width of "
-				"type");
+		    warning_at (location, OPT_Wshift_count_overflow,
+				"left shift count >= width of type");
 		}
 	    }
 
Index: c-family/c.opt
===================================================================
--- c-family/c.opt	(revision 217282)
+++ c-family/c.opt	(working copy)
@@ -760,14 +760,22 @@  Wselector
 ObjC ObjC++ Var(warn_selector) Warning
 Warn if a selector has multiple methods
 
+Wsequence-point
+C ObjC C++ ObjC++ Var(warn_sequence_point) Warning LangEnabledBy(C ObjC C++ ObjC++,Wall)
+Warn about possible violations of sequence point rules
+
 Wshadow-ivar
 ObjC ObjC++ Var(warn_shadow_ivar) EnabledBy(Wshadow) Init(1) Warning
 Warn if a local declaration hides an instance variable
 
-Wsequence-point
-C ObjC C++ ObjC++ Var(warn_sequence_point) Warning LangEnabledBy(C ObjC C++ ObjC++,Wall)
-Warn about possible violations of sequence point rules
+Wshift-count-negative
+C ObjC C++ ObjC++ Var(warn_shift_count_negative) Init(1) Warning
+Warn if left shift count is negative
 
+Wshift-count-overflow
+C ObjC C++ ObjC++ Var(warn_shift_count_overflow) Init(1) Warning
+Warn if left shift count >= width of type
+
 Wsign-compare
 C ObjC C++ ObjC++ Var(warn_sign_compare) Warning LangEnabledBy(C++ ObjC++,Wall)
 Warn about signed-unsigned comparisons
Index: cp/pt.c
===================================================================
--- cp/pt.c	(revision 217282)
+++ cp/pt.c	(working copy)
@@ -14680,6 +14680,8 @@  tsubst_copy_and_build (tree t,
       {
 	warning_sentinel s1(warn_type_limits);
 	warning_sentinel s2(warn_div_by_zero);
+	warning_sentinel s3(warn_shift_count_negative);
+	warning_sentinel s4(warn_shift_count_overflow);
 	tree op0 = RECUR (TREE_OPERAND (t, 0));
 	tree op1 = RECUR (TREE_OPERAND (t, 1));
 	tree r = build_x_binary_op
Index: cp/typeck.c
===================================================================
--- cp/typeck.c	(revision 217282)
+++ cp/typeck.c	(working copy)
@@ -4328,7 +4328,8 @@  cp_build_binary_op (location_t location,
 		{
 		  if ((complain & tf_warning)
 		      && c_inhibit_evaluation_warnings == 0)
-		    warning (0, "left shift count is negative");
+		    warning (OPT_Wshift_count_negative,
+			     "left shift count is negative");
 		}
 	      else if (compare_tree_int (const_op1,
 					 TYPE_PRECISION (type0)) >= 0)
@@ -4335,7 +4336,8 @@  cp_build_binary_op (location_t location,
 		{
 		  if ((complain & tf_warning)
 		      && c_inhibit_evaluation_warnings == 0)
-		    warning (0, "left shift count >= width of type");
+		    warning (OPT_Wshift_count_overflow,
+			     "left shift count >= width of type");
 		}
 	    }
 	  /* Convert the shift-count to an integer, regardless of
Index: doc/invoke.texi
===================================================================
--- doc/invoke.texi	(revision 217282)
+++ doc/invoke.texi	(working copy)
@@ -269,6 +269,7 @@  Objective-C and Objective-C++ Dialects}.
 -Wpointer-arith  -Wno-pointer-to-int-cast @gol
 -Wredundant-decls  -Wno-return-local-addr @gol
 -Wreturn-type  -Wsequence-point  -Wshadow  -Wno-shadow-ivar @gol
+-Wshift-count-negative -Wshift-count-overflow @gol
 -Wsign-compare  -Wsign-conversion -Wfloat-conversion @gol
 -Wsizeof-pointer-memaccess  -Wsizeof-array-argument @gol
 -Wstack-protector -Wstack-usage=@var{len} -Wstrict-aliasing @gol
@@ -3825,6 +3826,16 @@  exceptions are @samp{main} and functions defined i
 
 This warning is enabled by @option{-Wall}.
 
+@item -Wshift-count-negative
+@opindex Wshift-count-negative
+@opindex Wno-shift-count-negative
+Warn if left shift count is negative. This warning is enabled by default.
+
+@item -Wshift-count-overflow
+@opindex Wshift-count-overflow
+@opindex Wno-shift-count-overflow
+Warn if left shift count >= width of type. This warning is enabled by default.
+
 @item -Wswitch
 @opindex Wswitch
 @opindex Wno-switch
Index: testsuite/g++.dg/cpp0x/constexpr-63265.C
===================================================================
--- testsuite/g++.dg/cpp0x/constexpr-63265.C	(revision 0)
+++ testsuite/g++.dg/cpp0x/constexpr-63265.C	(working copy)
@@ -0,0 +1,19 @@ 
+// PR c++/63265
+// { dg-do compile { target c++11 } }
+
+#define LSHIFT (sizeof(unsigned int) * __CHAR_BIT__)
+
+template <int lshift>
+struct SpuriouslyWarns1 {
+    static constexpr unsigned int v = lshift < LSHIFT ? 1U << lshift : 0;
+};
+
+static_assert(SpuriouslyWarns1<LSHIFT>::v == 0, "Impossible occurred");
+
+template <int lshift>
+struct SpuriouslyWarns2 {
+    static constexpr bool okay = lshift < LSHIFT;
+    static constexpr unsigned int v = okay ? 1U << lshift : 0;
+};
+
+static_assert(SpuriouslyWarns2<LSHIFT>::v == 0, "Impossible occurred");