Index: docs/ReleaseNotes.rst
===================================================================
--- docs/ReleaseNotes.rst
+++ docs/ReleaseNotes.rst
@@ -71,6 +71,17 @@
   errors/warnings, as the system frameworks might add a method with the same
   selector which could make the message send to ``id`` ambiguous.
 
+- ``-Wtautological-compare`` warning on comparison of unsigned integer and
+  ``0`` constant was adjusted to warn regardless of whether the constant is
+  signed or unsigned.
+
+- ``-Wtautological-compare`` now warns about comparison of signed integer and
+  ``0U`` constant when appropriate.
+
+- ``-Wsign-compare`` was adjusted not to warn if ``-Wtautological-compare`` has
+  already warned about comparison of signed integer (which is automatically
+  promoted to an unsigned integer) and ``0U`` constant.
+
 Non-comprehensive list of changes in this release
 -------------------------------------------------
 
Index: lib/Sema/SemaChecking.cpp
===================================================================
--- lib/Sema/SemaChecking.cpp
+++ lib/Sema/SemaChecking.cpp
@@ -8567,32 +8567,51 @@
   return E->getType()->isEnumeralType();
 }
 
-void CheckTrivialUnsignedComparison(Sema &S, BinaryOperator *E) {
+bool isNonBooleanUnsignedValue(Expr *E) {
+  // We are checking that the expression is not known to have boolean value,
+  // is an integer type; and is either unsigned after implicit casts,
+  // or was unsigned before implicit casts.
+  return !E->isKnownToHaveBooleanValue() && E->getType()->isIntegerType() &&
+         (!E->getType()->isSignedIntegerType() ||
+          !E->IgnoreParenImpCasts()->getType()->isSignedIntegerType());
+}
+
+bool CheckTautologicalComparisonWithZero(Sema &S, BinaryOperator *E) {
   // Disable warning in template instantiations.
   if (S.inTemplateInstantiation())
-    return;
+    return false;
+
+  // bool values are handled by DiagnoseOutOfRangeComparison().
 
   BinaryOperatorKind op = E->getOpcode();
   if (E->isValueDependent())
-    return;
+    return false;
 
-  if (op == BO_LT && IsZero(S, E->getRHS())) {
+  Expr *LHS = E->getLHS();
+  Expr *RHS = E->getRHS();
+
+  bool Match = true;
+
+  if (op == BO_LT && isNonBooleanUnsignedValue(LHS) && IsZero(S, RHS)) {
     S.Diag(E->getOperatorLoc(), diag::warn_lunsigned_always_true_comparison)
-      << "< 0" << "false" << HasEnumType(E->getLHS())
-      << E->getLHS()->getSourceRange() << E->getRHS()->getSourceRange();
-  } else if (op == BO_GE && IsZero(S, E->getRHS())) {
+      << "< 0" << "false" << HasEnumType(LHS)
+      << LHS->getSourceRange() << RHS->getSourceRange();
+  } else if (op == BO_GE && isNonBooleanUnsignedValue(LHS) && IsZero(S, RHS)) {
     S.Diag(E->getOperatorLoc(), diag::warn_lunsigned_always_true_comparison)
-      << ">= 0" << "true" << HasEnumType(E->getLHS())
-      << E->getLHS()->getSourceRange() << E->getRHS()->getSourceRange();
-  } else if (op == BO_GT && IsZero(S, E->getLHS())) {
+      << ">= 0" << "true" << HasEnumType(LHS)
+      << LHS->getSourceRange() << RHS->getSourceRange();
+  } else if (op == BO_GT && isNonBooleanUnsignedValue(RHS) && IsZero(S, LHS)) {
     S.Diag(E->getOperatorLoc(), diag::warn_runsigned_always_true_comparison)
-      << "0 >" << "false" << HasEnumType(E->getRHS())
-      << E->getLHS()->getSourceRange() << E->getRHS()->getSourceRange();
-  } else if (op == BO_LE && IsZero(S, E->getLHS())) {
+      << "0 >" << "false" << HasEnumType(RHS)
+      << LHS->getSourceRange() << RHS->getSourceRange();
+  } else if (op == BO_LE && isNonBooleanUnsignedValue(RHS) && IsZero(S, LHS)) {
     S.Diag(E->getOperatorLoc(), diag::warn_runsigned_always_true_comparison)
-      << "0 <=" << "true" << HasEnumType(E->getRHS())
-      << E->getLHS()->getSourceRange() << E->getRHS()->getSourceRange();
-  }
+      << "0 <=" << "true" << HasEnumType(RHS)
+      << LHS->getSourceRange() << RHS->getSourceRange();
+  } else
+    Match = false;
+
+  return Match;
 }
 
 void DiagnoseOutOfRangeComparison(Sema &S, BinaryOperator *E, Expr *Constant,
@@ -8612,7 +8631,7 @@
 
   bool OtherIsBooleanType = Other->isKnownToHaveBooleanValue();
 
-  // 0 values are handled later by CheckTrivialUnsignedComparison().
+  // 0 values are handled later by CheckTautologicalComparisonWithZero().
   if ((Value == 0) && (!OtherIsBooleanType))
     return;
 
@@ -8849,16 +8868,23 @@
         (IsRHSIntegralLiteral && IsLHSIntegralLiteral);
   } else if (!T->hasUnsignedIntegerRepresentation())
       IsComparisonConstant = E->isIntegerConstantExpr(S.Context);
-  
+
+  // We don't care about value-dependent expressions or expressions
+  // whose result is a constant.
+  if (IsComparisonConstant)
+    return AnalyzeImpConvsInComparison(S, E);
+
+  // If this is a tautological comparison, bail out, do not potentially warn
+  // on -Wsign-compare
+  if(CheckTautologicalComparisonWithZero(S, E))
+    return AnalyzeImpConvsInComparison(S, E);
+
   // We don't do anything special if this isn't an unsigned integral
   // comparison:  we're only interested in integral comparisons, and
   // signed comparisons only happen in cases we don't care to warn about.
-  //
-  // We also don't care about value-dependent expressions or expressions
-  // whose result is a constant.
-  if (!T->hasUnsignedIntegerRepresentation() || IsComparisonConstant)
+  if (!T->hasUnsignedIntegerRepresentation())
     return AnalyzeImpConvsInComparison(S, E);
-  
+
   // Check to see if one of the (unmodified) operands is of different
   // signedness.
   Expr *signedOperand, *unsignedOperand;
@@ -8871,7 +8897,6 @@
     signedOperand = RHS;
     unsignedOperand = LHS;
   } else {
-    CheckTrivialUnsignedComparison(S, E);
     return AnalyzeImpConvsInComparison(S, E);
   }
 
@@ -8883,11 +8908,9 @@
   AnalyzeImplicitConversions(S, LHS, E->getOperatorLoc());
   AnalyzeImplicitConversions(S, RHS, E->getOperatorLoc());
 
-  // If the signed range is non-negative, -Wsign-compare won't fire,
-  // but we should still check for comparisons which are always true
-  // or false.
+  // If the signed range is non-negative, -Wsign-compare won't fire.
   if (signedRange.NonNegative)
-    return CheckTrivialUnsignedComparison(S, E);
+    return;
 
   // For (in)equality comparisons, if the unsigned operand is a
   // constant which cannot collide with a overflowed signed operand,
Index: test/Sema/compare.c
===================================================================
--- test/Sema/compare.c
+++ test/Sema/compare.c
@@ -77,7 +77,7 @@
          ((int) a == (unsigned int) B) +
          ((short) a == (unsigned short) B) +
          ((signed char) a == (unsigned char) B) +
-         (a < (unsigned long) B) +  // expected-warning {{comparison of integers of different signs}}
+         (a < (unsigned long) B) +  // expected-warning {{comparison of unsigned expression < 0 is always false}}
          (a < (unsigned int) B) +
          (a < (unsigned short) B) +
          (a < (unsigned char) B) +
@@ -85,8 +85,8 @@
          ((int) a < B) +
          ((short) a < B) +
          ((signed char) a < B) +
-         ((long) a < (unsigned long) B) +  // expected-warning {{comparison of integers of different signs}}
-         ((int) a < (unsigned int) B) +  // expected-warning {{comparison of integers of different signs}}
+         ((long) a < (unsigned long) B) +  // expected-warning {{comparison of unsigned expression < 0 is always false}}
+         ((int) a < (unsigned int) B) +  // expected-warning {{comparison of unsigned expression < 0 is always false}}
          ((short) a < (unsigned short) B) +
          ((signed char) a < (unsigned char) B) +
 
Index: test/Sema/outof-range-constant-compare.c
===================================================================
--- test/Sema/outof-range-constant-compare.c
+++ test/Sema/outof-range-constant-compare.c
@@ -6,6 +6,59 @@
 int main()
 {
     int a = value();
+
+    if (a == 0x0000000000000000L)
+        return 0;
+    if (a != 0x0000000000000000L)
+        return 0;
+    if (a < 0x0000000000000000L)
+        return 0;
+    if (a <= 0x0000000000000000L)
+        return 0;
+    if (a > 0x0000000000000000L)
+        return 0;
+    if (a >= 0x0000000000000000L)
+        return 0;
+
+    if (0x0000000000000000L == a)
+        return 0;
+    if (0x0000000000000000L != a)
+        return 0;
+    if (0x0000000000000000L < a)
+        return 0;
+    if (0x0000000000000000L <= a)
+        return 0;
+    if (0x0000000000000000L > a)
+        return 0;
+    if (0x0000000000000000L >= a)
+        return 0;
+
+    if (a == 0x0000000000000000UL)
+        return 0;
+    if (a != 0x0000000000000000UL)
+        return 0;
+    if (a < 0x0000000000000000UL) // expected-warning {{comparison of unsigned expression < 0 is always false}}
+        return 0;
+    if (a <= 0x0000000000000000UL)
+        return 0;
+    if (a > 0x0000000000000000UL)
+        return 0;
+    if (a >= 0x0000000000000000UL) // expected-warning {{comparison of unsigned expression >= 0 is always true}}
+        return 0;
+
+    if (0x0000000000000000UL == a)
+        return 0;
+    if (0x0000000000000000UL != a)
+        return 0;
+    if (0x0000000000000000UL < a)
+        return 0;
+    if (0x0000000000000000UL <= a) // expected-warning {{comparison of 0 <= unsigned expression is always true}}
+        return 0;
+    if (0x0000000000000000UL > a) // expected-warning {{comparison of 0 > unsigned expression is always false}}
+        return 0;
+    if (0x0000000000000000UL >= a)
+        return 0;
+
     if (a == 0x1234567812345678L) // expected-warning {{comparison of constant 1311768465173141112 with expression of type 'int' is always false}}
         return 0;
     if (a != 0x1234567812345678L) // expected-warning {{comparison of constant 1311768465173141112 with expression of type 'int' is always true}}
@@ -74,6 +127,7 @@
         return 0;
     if (0x1234567812345678L >= s) // expected-warning {{comparison of constant 1311768465173141112 with expression of type 'short' is always true}}
         return 0;
+
     long l = value();
     if (l == 0x1234567812345678L)
         return 0;
@@ -106,13 +160,13 @@
         return 0;
     if (un != 0x0000000000000000L)
         return 0;
-    if (un < 0x0000000000000000L)
+    if (un < 0x0000000000000000L) // expected-warning {{comparison of unsigned expression < 0 is always false}}
         return 0;
     if (un <= 0x0000000000000000L)
         return 0;
     if (un > 0x0000000000000000L)
         return 0;
-    if (un >= 0x0000000000000000L)
+    if (un >= 0x0000000000000000L) // expected-warning {{comparison of unsigned expression >= 0 is always true}}
         return 0;
 
     if (0x0000000000000000L == un)
@@ -121,19 +175,92 @@
         return 0;
     if (0x0000000000000000L < un)
         return 0;
-    if (0x0000000000000000L <= un)
+    if (0x0000000000000000L <= un) // expected-warning {{comparison of 0 <= unsigned expression is always true}}
         return 0;
-    if (0x0000000000000000L > un)
+    if (0x0000000000000000L > un) // expected-warning {{comparison of 0 > unsigned expression is always false}}
         return 0;
     if (0x0000000000000000L >= un)
         return 0;
-    float fl = 0;
-    if (fl == 0x0000000000000000L) // no warning
-      return 0;
 
-    float dl = 0;
-    if (dl == 0x0000000000000000L) // no warning
-      return 0;
+    if (un == 0x0000000000000000UL)
+        return 0;
+    if (un != 0x0000000000000000UL)
+        return 0;
+    if (un < 0x0000000000000000UL) // expected-warning {{comparison of unsigned expression < 0 is always false}}
+        return 0;
+    if (un <= 0x0000000000000000UL)
+        return 0;
+    if (un > 0x0000000000000000UL)
+        return 0;
+    if (un >= 0x0000000000000000UL) // expected-warning {{comparison of unsigned expression >= 0 is always true}}
+        return 0;
+
+    if (0x0000000000000000UL == un)
+        return 0;
+    if (0x0000000000000000UL != un)
+        return 0;
+    if (0x0000000000000000UL < un)
+        return 0;
+    if (0x0000000000000000UL <= un) // expected-warning {{comparison of 0 <= unsigned expression is always true}}
+        return 0;
+    if (0x0000000000000000UL > un) // expected-warning {{comparison of 0 > unsigned expression is always false}}
+        return 0;
+    if (0x0000000000000000UL >= un)
+        return 0;
+
+    float fl = 0;
+    if (fl == 0x0000000000000000L)
+        return 0;
+    if (fl != 0x0000000000000000L)
+        return 0;
+    if (fl < 0x0000000000000000L)
+        return 0;
+    if (fl <= 0x0000000000000000L)
+        return 0;
+    if (fl > 0x0000000000000000L)
+        return 0;
+    if (fl >= 0x0000000000000000L)
+        return 0;
+
+    if (0x0000000000000000L == fl)
+        return 0;
+    if (0x0000000000000000L != fl)
+        return 0;
+    if (0x0000000000000000L < fl)
+        return 0;
+    if (0x0000000000000000L <= fl)
+        return 0;
+    if (0x0000000000000000L > fl)
+        return 0;
+    if (0x0000000000000000L >= fl)
+        return 0;
+
+    double dl = 0;
+    if (dl == 0x0000000000000000L)
+        return 0;
+    if (dl != 0x0000000000000000L)
+        return 0;
+    if (dl < 0x0000000000000000L)
+        return 0;
+    if (dl <= 0x0000000000000000L)
+        return 0;
+    if (dl > 0x0000000000000000L)
+        return 0;
+    if (dl >= 0x0000000000000000L)
+        return 0;
+
+    if (0x0000000000000000L == dl)
+        return 0;
+    if (0x0000000000000000L != dl)
+        return 0;
+    if (0x0000000000000000L < dl)
+        return 0;
+    if (0x0000000000000000L <= dl)
+        return 0;
+    if (0x0000000000000000L > dl)
+        return 0;
+    if (0x0000000000000000L >= dl)
+        return 0;
 
     enum E {
     yes,
Index: test/SemaCXX/compare.cpp
===================================================================
--- test/SemaCXX/compare.cpp
+++ test/SemaCXX/compare.cpp
@@ -73,7 +73,7 @@
          ((int) a == (unsigned int) B) +
          ((short) a == (unsigned short) B) +
          ((signed char) a == (unsigned char) B) +
-         (a < (unsigned long) B) +  // expected-warning {{comparison of integers of different signs}}
+         (a < (unsigned long) B) +  // expected-warning {{comparison of unsigned expression < 0 is always false}}
          (a < (unsigned int) B) +
          (a < (unsigned short) B) +
          (a < (unsigned char) B) +
@@ -81,8 +81,8 @@
          ((int) a < B) +
          ((short) a < B) +
          ((signed char) a < B) +
-         ((long) a < (unsigned long) B) +  // expected-warning {{comparison of integers of different signs}}
-         ((int) a < (unsigned int) B) +  // expected-warning {{comparison of integers of different signs}}
+         ((long) a < (unsigned long) B) +  // expected-warning {{comparison of unsigned expression < 0 is always false}}
+         ((int) a < (unsigned int) B) +  // expected-warning {{comparison of unsigned expression < 0 is always false}}
          ((short) a < (unsigned short) B) +
          ((signed char) a < (unsigned char) B) +