Index: gcc/testsuite/g++.dg/conversion/nullptr1.C
===================================================================
--- gcc/testsuite/g++.dg/conversion/nullptr1.C	(revision 120546)
+++ gcc/testsuite/g++.dg/conversion/nullptr1.C	(working copy)
@@ -1,10 +0,0 @@
-/* Test for overflow in NULL pointer constant.  */
-/* { dg-do compile } */
-
-#include <limits.h>
-
-void *p = 0;
-
-void *q = 0 * (INT_MAX + 1);  // { dg-error "invalid conversion" }
-
-
Index: gcc/testsuite/g++.dg/warn/overflow-warn-3.C
===================================================================
--- gcc/testsuite/g++.dg/warn/overflow-warn-3.C	(revision 0)
+++ gcc/testsuite/g++.dg/warn/overflow-warn-3.C	(revision 0)
@@ -0,0 +1,130 @@
+/* Test for diagnostics for constant overflow.  Test with -pedantic.  */
+/* Origin: Joseph Myers <joseph@codesourcery.com> */
+/* { dg-do compile } */
+/* { dg-options "-fpermissive -pedantic" } */
+
+#include <limits.h>
+
+enum e {
+  E0 = INT_MAX,
+  /* Unsigned overflow wraps around.  */
+  E1 = UINT_MAX + 1,
+  /* Overflow in an unevaluated part of an expression is OK (example
+     in the standard).  */
+  E2 = 2 || 1 / 0, /* { dg-bogus "warning: division by zero" "" { xfail *-*-* } 14 } */
+  E3 = 1 / 0, /* { dg-warning "warning: division by zero" } */
+  /* { dg-error "error: enumerator value for 'E3' is not an integer constant" "enum error" { target *-*-* } 15 } */
+  /* But as in DR#031, the 1/0 in an evaluated subexpression means the
+     whole expression violates the constraints.  */
+  E4 = 0 * (1 / 0), /* { dg-warning "warning: division by zero" } */
+  /* { dg-error "error: enumerator value for 'E4' is not an integer constant" "enum error" { xfail *-*-* } 19 } */
+  E5 = INT_MAX + 1, /* { dg-warning "warning: integer overflow in expression" } */
+  /* { dg-warning "warning: overflow in constant expression" "constant" { target *-*-* } 21 } */
+  /* Again, overflow in evaluated subexpression.  */
+  E6 = 0 * (INT_MAX + 1), /* { dg-warning "warning: integer overflow in expression" } */
+  /* { dg-warning "warning: overflow in constant expression" "constant" { target *-*-* } 24 } */
+  /* A cast does not constitute overflow in conversion.  */
+  E7 = (char) INT_MAX
+};
+
+struct s {
+  int a;
+  int : 0 * (1 / 0); /* { dg-warning "warning: division by zero" } */
+  int : 0 * (INT_MAX + 1); /* { dg-warning "warning: integer overflow in expression" } */
+  /* { dg-warning "warning: overflow in constant expression" "constant" { target *-*-* } 33 } */
+};
+
+void
+f (void)
+{
+  /* This expression is not required to be a constant expression, so
+     it should just involve undefined behavior at runtime.  */
+  int c = INT_MAX + 1; /* { dg-warning "warning: integer overflow in expression" } */
+
+}
+
+/* This expression is neither required to be constant.  */
+static int sc = INT_MAX + 1; /* { dg-warning "warning: integer overflow in expression" } */
+
+
+// Test for overflow in null pointer constant.  
+void *n = 0;
+/* The first two of these involve overflow, so are not null pointer
+   constants.  The third has the overflow in an unevaluated
+   subexpression, so is a null pointer constant.  */
+void *p = 0 * (INT_MAX + 1); /* { dg-warning "warning: integer overflow in expression" } */
+/* { dg-error "invalid conversion from 'int' to 'void" "null" { target *-*-* } 55 } */
+
+void *q = 0 * (1 / 0); /* { dg-warning "warning: division by zero" } */
+/* { dg-error "invalid conversion from 'int' to 'void*'" "null" { xfail *-*-* } 58 } */
+void *r = (1 ? 0 : INT_MAX+1); /* { dg-bogus "integer overflow in expression" "" { xfail *-*-* } 60 } */
+
+void
+g (int i)
+{
+  switch (i)
+    {
+    case 0 * (1/0): /* { dg-warning "warning: division by zero" } */
+      ;
+    case 1 + 0 * (INT_MAX + 1): /* { dg-warning "warning: integer overflow in expression" } */
+      /* { dg-warning "warning: overflow in constant expression" "constant" { target *-*-* } 69 } */
+      ;
+    }
+}
+
+int
+h (void)
+{
+  return INT_MAX + 1; /* { dg-warning "warning: integer overflow in expression" } */
+}
+
+int
+h1 (void)
+{
+  return INT_MAX + 1 - INT_MAX; /* { dg-warning "warning: integer overflow in expression" } */
+}
+
+void fuc (unsigned char);
+void fsc (signed char);
+
+void
+h2 (void)
+{
+  fsc (SCHAR_MAX + 1); /* { dg-warning "warning: overflow in implicit constant conversion" } */
+  fsc (SCHAR_MIN - 1); /* { dg-warning "warning: overflow in implicit constant conversion" } */
+  fsc (UCHAR_MAX); /* { dg-warning "warning: overflow in implicit constant conversion" } */
+  fsc (UCHAR_MAX + 1); /* { dg-warning "warning: overflow in implicit constant conversion" } */
+  fuc (-1);
+  fuc (UCHAR_MAX + 1); /* { dg-warning "warning: large integer implicitly truncated to unsigned type" } */
+  fuc (SCHAR_MIN);
+  fuc (SCHAR_MIN - 1); /* { dg-warning "warning: large integer implicitly truncated to unsigned type" } */
+  fuc (-UCHAR_MAX); /* { dg-warning "warning: large integer implicitly truncated to unsigned type" } */
+}
+
+void fui (unsigned int);
+void fsi (signed int);
+
+int si;
+unsigned ui;
+
+void
+h2i (int x)
+{
+  /* For some reason, we only give certain warnings for implicit
+     conversions among values of the same precision with -Wconversion,
+     while we don't give others at all.  */
+  fsi ((unsigned)INT_MAX + 1);
+  si = (unsigned)INT_MAX + 1;
+  si = x ? (unsigned)INT_MAX + 1 : 1;
+  fsi ((unsigned)INT_MAX + 2);
+  si = (unsigned)INT_MAX + 2;
+  si = x ? (unsigned)INT_MAX + 2 : 1;
+  fsi (UINT_MAX);
+  si = UINT_MAX;
+  fui (-1);
+  ui = -1;
+  ui = x ? -1 : 1U;
+  fui (INT_MIN);
+  ui = INT_MIN;
+  ui = x ? INT_MIN : 1U;
+}
Index: gcc/testsuite/g++.dg/warn/Woverflow-2.C
===================================================================
--- gcc/testsuite/g++.dg/warn/Woverflow-2.C	(revision 0)
+++ gcc/testsuite/g++.dg/warn/Woverflow-2.C	(revision 0)
@@ -0,0 +1,7 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -Woverflow" } */
+
+#include <limits.h>
+
+int foo = INT_MAX + 1;  /* { dg-warning "integer overflow" } */
+
Index: gcc/testsuite/g++.dg/warn/overflow-warn-4.C
===================================================================
--- gcc/testsuite/g++.dg/warn/overflow-warn-4.C	(revision 0)
+++ gcc/testsuite/g++.dg/warn/overflow-warn-4.C	(revision 0)
@@ -0,0 +1,130 @@
+/* Test for diagnostics for constant overflow.  Test with -pedantic-errors.  */
+/* Origin: Joseph Myers <joseph@codesourcery.com> */
+/* { dg-do compile } */
+/* { dg-options "-pedantic-errors" } */
+
+#include <limits.h>
+
+enum e {
+  E0 = INT_MAX,
+  /* Unsigned overflow wraps around.  */
+  E1 = UINT_MAX + 1,
+  /* Overflow in an unevaluated part of an expression is OK (example
+     in the standard).  */
+  E2 = 2 || 1 / 0, /* { dg-bogus "warning: division by zero" "" { xfail *-*-* } 14 } */
+  E3 = 1 / 0, /* { dg-warning "warning: division by zero" } */
+  /* { dg-error "error: enumerator value for 'E3' is not an integer constant" "enum error" { target *-*-* } 15 } */
+  /* But as in DR#031, the 1/0 in an evaluated subexpression means the
+     whole expression violates the constraints.  */
+  E4 = 0 * (1 / 0), /* { dg-warning "warning: division by zero" } */
+  /* { dg-error "error: enumerator value for 'E4' is not an integer constant" "enum error" { xfail *-*-* } 19 } */
+  E5 = INT_MAX + 1, /* { dg-warning "warning: integer overflow in expression" } */
+  /* { dg-error "error: overflow in constant expression" "constant" { target *-*-* } 21 } */
+  /* Again, overflow in evaluated subexpression.  */
+  E6 = 0 * (INT_MAX + 1), /* { dg-warning "warning: integer overflow in expression" } */
+  /* { dg-error "error: overflow in constant expression" "constant" { target *-*-* } 24 } */
+  /* A cast does not constitute overflow in conversion.  */
+  E7 = (char) INT_MAX
+};
+
+struct s {
+  int a;
+  int : 0 * (1 / 0); /* { dg-warning "warning: division by zero" } */
+  int : 0 * (INT_MAX + 1); /* { dg-warning "warning: integer overflow in expression" } */
+  /* { dg-error "error: overflow in constant expression" "constant" { target *-*-* } 33 } */
+};
+
+void
+f (void)
+{
+  /* This expression is not required to be a constant expression, so
+     it should just involve undefined behavior at runtime.  */
+  int c = INT_MAX + 1; /* { dg-warning "warning: integer overflow in expression" } */
+
+}
+
+/* This expression is neither required to be constant.  */
+static int sc = INT_MAX + 1; /* { dg-warning "warning: integer overflow in expression" } */
+
+
+// Test for overflow in null pointer constant.  
+void *n = 0;
+/* The first two of these involve overflow, so are not null pointer
+   constants.  The third has the overflow in an unevaluated
+   subexpression, so is a null pointer constant.  */
+void *p = 0 * (INT_MAX + 1); /* { dg-warning "warning: integer overflow in expression" } */
+/* { dg-error "invalid conversion from 'int' to 'void" "null" { target *-*-* } 55 } */
+
+void *q = 0 * (1 / 0); /* { dg-warning "warning: division by zero" } */
+/* { dg-error "invalid conversion from 'int' to 'void*'" "null" { xfail *-*-* } 58 } */
+void *r = (1 ? 0 : INT_MAX+1); /* { dg-bogus "integer overflow in expression" "" { xfail *-*-* } 60 } */
+
+void
+g (int i)
+{
+  switch (i)
+    {
+    case 0 * (1/0): /* { dg-warning "warning: division by zero" } */
+      ;
+    case 1 + 0 * (INT_MAX + 1): /* { dg-warning "warning: integer overflow in expression" } */
+      /* { dg-error "error: overflow in constant expression" "constant" { target *-*-* } 69 } */
+      ;
+    }
+}
+
+int
+h (void)
+{
+  return INT_MAX + 1; /* { dg-warning "warning: integer overflow in expression" } */
+}
+
+int
+h1 (void)
+{
+  return INT_MAX + 1 - INT_MAX; /* { dg-warning "warning: integer overflow in expression" } */
+}
+
+void fuc (unsigned char);
+void fsc (signed char);
+
+void
+h2 (void)
+{
+  fsc (SCHAR_MAX + 1); /* { dg-warning "warning: overflow in implicit constant conversion" } */
+  fsc (SCHAR_MIN - 1); /* { dg-warning "warning: overflow in implicit constant conversion" } */
+  fsc (UCHAR_MAX); /* { dg-warning "warning: overflow in implicit constant conversion" } */
+  fsc (UCHAR_MAX + 1); /* { dg-warning "warning: overflow in implicit constant conversion" } */
+  fuc (-1);
+  fuc (UCHAR_MAX + 1); /* { dg-warning "warning: large integer implicitly truncated to unsigned type" } */
+  fuc (SCHAR_MIN);
+  fuc (SCHAR_MIN - 1); /* { dg-warning "warning: large integer implicitly truncated to unsigned type" } */
+  fuc (-UCHAR_MAX); /* { dg-warning "warning: large integer implicitly truncated to unsigned type" } */
+}
+
+void fui (unsigned int);
+void fsi (signed int);
+
+int si;
+unsigned ui;
+
+void
+h2i (int x)
+{
+  /* For some reason, we only give certain warnings for implicit
+     conversions among values of the same precision with -Wconversion,
+     while we don't give others at all.  */
+  fsi ((unsigned)INT_MAX + 1);
+  si = (unsigned)INT_MAX + 1;
+  si = x ? (unsigned)INT_MAX + 1 : 1;
+  fsi ((unsigned)INT_MAX + 2);
+  si = (unsigned)INT_MAX + 2;
+  si = x ? (unsigned)INT_MAX + 2 : 1;
+  fsi (UINT_MAX);
+  si = UINT_MAX;
+  fui (-1);
+  ui = -1;
+  ui = x ? -1 : 1U;
+  fui (INT_MIN);
+  ui = INT_MIN;
+  ui = x ? INT_MIN : 1U;
+}
Index: gcc/testsuite/g++.dg/warn/Woverflow-3.C
===================================================================
--- gcc/testsuite/g++.dg/warn/Woverflow-3.C	(revision 0)
+++ gcc/testsuite/g++.dg/warn/Woverflow-3.C	(revision 0)
@@ -0,0 +1,7 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -Wno-overflow" } */
+
+#include <limits.h>
+
+int foo = INT_MAX + 1;
+
Index: gcc/testsuite/g++.dg/warn/multiple-overflow-warn-2.C
===================================================================
--- gcc/testsuite/g++.dg/warn/multiple-overflow-warn-2.C	(revision 0)
+++ gcc/testsuite/g++.dg/warn/multiple-overflow-warn-2.C	(revision 0)
@@ -0,0 +1,12 @@
+/* PR c/19978 : Test for duplicated warnings (binary operators).  */
+/* { dg-do compile } */
+/* { dg-options "-Woverflow" } */
+
+#include <limits.h>
+
+int 
+g1 (void)
+{
+  return INT_MAX + 1 - INT_MAX; /* { dg-bogus "integer overflow in expression.*integer overflow in expression" } */
+  /* { dg-warning "integer overflow in expression" "" { target *-*-* } 10 } */
+}
Index: gcc/testsuite/g++.dg/warn/overflow-warn-1.C
===================================================================
--- gcc/testsuite/g++.dg/warn/overflow-warn-1.C	(revision 0)
+++ gcc/testsuite/g++.dg/warn/overflow-warn-1.C	(revision 0)
@@ -0,0 +1,124 @@
+/* Test for diagnostics for constant overflow.  */
+/* Origin: Joseph Myers <joseph@codesourcery.com> */
+/* { dg-do compile } */
+/* { dg-options "" } */
+
+#include <limits.h>
+
+enum e {
+  E0 = INT_MAX,
+  /* Unsigned overflow wraps around.  */
+  E1 = UINT_MAX + 1,
+  /* Overflow in an unevaluated part of an expression is OK (example
+     in the standard).  */
+  E2 = 2 || 1 / 0, /* { dg-bogus "warning: division by zero" "" { xfail *-*-* } 14 } */
+  E3 = 1 / 0, /* { dg-warning "warning: division by zero" } */
+  /* { dg-error "error: enumerator value for 'E3' is not an integer constant" "enum error" { target *-*-* } 15 } */
+  /* But as in DR#031, the 1/0 in an evaluated subexpression means the
+     whole expression violates the constraints.  */
+  E4 = 0 * (1 / 0), /* { dg-warning "warning: division by zero" } */
+  /* { dg-error "error: enumerator value for 'E4' is not an integer constant" "enum error" { xfail *-*-* } 19 } */
+  E5 = INT_MAX + 1, /* { dg-warning "warning: integer overflow in expression" } */
+  /* Again, overflow in evaluated subexpression.  */
+  E6 = 0 * (INT_MAX + 1), /* { dg-warning "warning: integer overflow in expression" } */
+  /* A cast does not constitute overflow in conversion.  */
+  E7 = (char) INT_MAX
+};
+
+struct s {
+  int a;
+  int : 0 * (1 / 0); /* { dg-warning "warning: division by zero" } */
+  int : 0 * (INT_MAX + 1); /* { dg-warning "warning: integer overflow in expression" } */
+};
+
+void
+f (void)
+{
+  /* This expression is not required to be a constant expression, so
+     it should just involve undefined behavior at runtime.  */
+  int c = INT_MAX + 1; /* { dg-warning "warning: integer overflow in expression" } */
+}
+
+/* This expression is neither required to be constant.  */
+static int sc = INT_MAX + 1; /* { dg-warning "warning: integer overflow in expression" } */
+
+
+// Test for overflow in null pointer constant.  
+void *n = 0;
+/* The first two of these involve overflow, so are not null pointer
+   constants.  The third has the overflow in an unevaluated
+   subexpression, so is a null pointer constant.  */
+void *p = 0 * (INT_MAX + 1); /* { dg-warning "warning: integer overflow in expression" } */
+/* { dg-error "invalid conversion from 'int' to 'void" "null" { target *-*-* } 51 } */
+void *q = 0 * (1 / 0); /* { dg-warning "warning: division by zero" } */
+/* { dg-error "invalid conversion from 'int' to 'void*'" "null" { xfail *-*-* } 53 } */
+void *r = (1 ? 0 : INT_MAX+1); /* { dg-bogus "integer overflow in expression" "" { xfail *-*-* } 55 } */
+
+void
+g (int i)
+{
+  switch (i)
+    {
+    case 0 * (1/0): /* { dg-warning "warning: division by zero" } */
+      ;
+    case 1 + 0 * (INT_MAX + 1): /* { dg-warning "warning: integer overflow in expression" } */
+      ;
+    }
+}
+
+int
+h (void)
+{
+  return INT_MAX + 1; /* { dg-warning "warning: integer overflow in expression" } */
+}
+
+int
+h1 (void)
+{
+  return INT_MAX + 1 - INT_MAX; /* { dg-warning "warning: integer overflow in expression" } */
+}
+
+void fuc (unsigned char);
+void fsc (signed char);
+
+void
+h2 (void)
+{
+  fsc (SCHAR_MAX + 1);
+  fsc (SCHAR_MIN - 1); /* { dg-warning "warning: overflow in implicit constant conversion" } */
+  fsc (UCHAR_MAX);
+  fsc (UCHAR_MAX + 1); /* { dg-warning "warning: overflow in implicit constant conversion" } */
+  fuc (-1);
+  fuc (UCHAR_MAX + 1); /* { dg-warning "warning: large integer implicitly truncated to unsigned type" } */
+  fuc (SCHAR_MIN);
+  fuc (SCHAR_MIN - 1); /* { dg-warning "warning: large integer implicitly truncated to unsigned type" } */
+  fuc (-UCHAR_MAX); /* { dg-warning "warning: large integer implicitly truncated to unsigned type" } */
+}
+
+void fui (unsigned int);
+void fsi (signed int);
+
+int si;
+unsigned ui;
+
+void
+h2i (int x)
+{
+  /* For some reason, we only give certain warnings for implicit
+     conversions among values of the same precision with -Wconversion,
+     while we don't give others at all.  */
+  fsi ((unsigned)INT_MAX + 1);
+  si = (unsigned)INT_MAX + 1;
+  si = x ? (unsigned)INT_MAX + 1 : 1;
+  fsi ((unsigned)INT_MAX + 2);
+  si = (unsigned)INT_MAX + 2;
+  si = x ? (unsigned)INT_MAX + 2 : 1;
+  fsi (UINT_MAX);
+  si = UINT_MAX;
+  fui (-1);
+  ui = -1;
+  ui = x ? -1 : 1U;
+  fui (INT_MIN);
+  ui = INT_MIN;
+  ui = x ? INT_MIN : 1U;
+}
Index: gcc/testsuite/g++.dg/warn/overflow-warn-5.C
===================================================================
--- gcc/testsuite/g++.dg/warn/overflow-warn-5.C	(revision 0)
+++ gcc/testsuite/g++.dg/warn/overflow-warn-5.C	(revision 0)
@@ -0,0 +1,7 @@
+/* PR c/27273 */
+/* { dg-do compile } */
+/* { dg-options "-Woverflow" } */
+
+unsigned char rx_async(unsigned char p) {
+    return p & 512; /* { dg-warning "overflow in implicit constant conversion" } */
+}
Index: gcc/testsuite/g++.dg/warn/overflow-warn-6.C
===================================================================
--- gcc/testsuite/g++.dg/warn/overflow-warn-6.C	(revision 0)
+++ gcc/testsuite/g++.dg/warn/overflow-warn-6.C	(revision 0)
@@ -0,0 +1,18 @@
+/* Test non-constant operands in overflowed expressions.  */
+/* { dg-do compile } */
+/* { dg-options "-Woverflow" } */
+
+#include <limits.h>
+
+int 
+h1 (int x)
+{
+  return x * (0 * (INT_MAX + 1)); /* { dg-warning "warning: integer overflow in expression" } */
+}
+
+int 
+h2 (int x)
+{
+  return ((INT_MAX + 1) * 0) * x; /* { dg-warning "warning: integer overflow in expression" } */
+}
+
Index: gcc/testsuite/g++.dg/warn/Woverflow-1.C
===================================================================
--- gcc/testsuite/g++.dg/warn/Woverflow-1.C	(revision 0)
+++ gcc/testsuite/g++.dg/warn/Woverflow-1.C	(revision 0)
@@ -0,0 +1,7 @@
+/* { dg-do compile } */
+/* { dg-options "-O2" } */
+
+#include <limits.h>
+
+int foo = INT_MAX + 1;  /* { dg-warning "integer overflow" } */
+
Index: gcc/cp/typeck.c
===================================================================
--- gcc/cp/typeck.c	(revision 120546)
+++ gcc/cp/typeck.c	(working copy)
@@ -3870,6 +3870,12 @@
   result = fold_if_not_in_template (result);
   if (final_type != 0)
     result = cp_convert (final_type, result);
+
+  if (TREE_OVERFLOW_P (result) 
+      && !TREE_OVERFLOW_P (op0) 
+      && !TREE_OVERFLOW_P (op1))
+    overflow_warning (result);
+
   return result;
 }