Move the warning about unused relational comparison from -Wunused-value to

-Wunused-comparison.  Also, newly warn on unused result from overloaded
relational comparisons, now also in -Wunused-comparison.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@203535 91177308-0d34-0410-b5e6-96231b3b80d8

include/clang/Basic/DiagnosticSemaKinds.td

@@ -5813,7 +5813,7 @@ def warn_unused_volatile : Warning<
   InGroup<DiagGroup<"unused-volatile-lvalue">>;
 
 def warn_unused_comparison : Warning<
-  "%select{equality|inequality}0 comparison result unused">,
+  "%select{%select{|in}1equality|relational}0 comparison result unused">,
   InGroup<UnusedComparison>;
 def note_inequality_comparison_to_or_assign : Note<
   "use '|=' to turn this inequality comparison into an or-assignment">;

lib/AST/Expr.cpp

@@ -2064,15 +2064,22 @@ bool Expr::isUnusedResultAWarning(const Expr *&WarnE, SourceLocation &Loc,
     return true;
 
   case CXXOperatorCallExprClass: {
-    // We warn about operator== and operator!= even when user-defined operator
+    // Warn about operator ==,!=,<,>,<=, and >= even when user-defined operator
     // overloads as there is no reasonable way to define these such that they
     // have non-trivial, desirable side-effects. See the -Wunused-comparison
-    // warning: these operators are commonly typo'ed, and so warning on them
+    // warning: operators == and != are commonly typo'ed, and so warning on them
     // provides additional value as well. If this list is updated,
     // DiagnoseUnusedComparison should be as well.
     const CXXOperatorCallExpr *Op = cast<CXXOperatorCallExpr>(this);
-    if (Op->getOperator() == OO_EqualEqual ||
-        Op->getOperator() == OO_ExclaimEqual) {
+    switch (Op->getOperator()) {
+    default:
+      break;
+    case OO_EqualEqual:
+    case OO_ExclaimEqual:
+    case OO_Less:
+    case OO_Greater:
+    case OO_GreaterEqual:
+    case OO_LessEqual:
       WarnE = this;
       Loc = Op->getOperatorLoc();
       R1 = Op->getSourceRange();

lib/Sema/SemaStmt.cpp

@@ -114,25 +114,38 @@ void Sema::ActOnForEachDeclStmt(DeclGroupPtrTy dg) {
   }
 }
 
-/// \brief Diagnose unused '==' and '!=' as likely typos for '=' or '|='.
+/// \brief Diagnose unused comparisons, both builtin and overloaded operators.
+/// For '==' and '!=', suggest fixits for '=' or '|='.
 ///
 /// Adding a cast to void (or other expression wrappers) will prevent the
 /// warning from firing.
 static bool DiagnoseUnusedComparison(Sema &S, const Expr *E) {
   SourceLocation Loc;
-  bool IsNotEqual, CanAssign;
+  bool IsNotEqual, CanAssign, IsRelational;
 
   if (const BinaryOperator *Op = dyn_cast<BinaryOperator>(E)) {
-    if (Op->getOpcode() != BO_EQ && Op->getOpcode() != BO_NE)
+    if (!Op->isComparisonOp())
       return false;
 
+    IsRelational = Op->isRelationalOp();
     Loc = Op->getOperatorLoc();
     IsNotEqual = Op->getOpcode() == BO_NE;
     CanAssign = Op->getLHS()->IgnoreParenImpCasts()->isLValue();
   } else if (const CXXOperatorCallExpr *Op = dyn_cast<CXXOperatorCallExpr>(E)) {
-    if (Op->getOperator() != OO_EqualEqual &&
-        Op->getOperator() != OO_ExclaimEqual)
+    switch (Op->getOperator()) {
+    default:
       return false;
+    case OO_EqualEqual:
+    case OO_ExclaimEqual:
+      IsRelational = false;
+      break;
+    case OO_Less:
+    case OO_Greater:
+    case OO_GreaterEqual:
+    case OO_LessEqual:
+      IsRelational = true;
+      break;
+    }
 
     Loc = Op->getOperatorLoc();
     IsNotEqual = Op->getOperator() == OO_ExclaimEqual;
@@ -148,11 +161,11 @@ static bool DiagnoseUnusedComparison(Sema &S, const Expr *E) {
     return false;
 
   S.Diag(Loc, diag::warn_unused_comparison)
-    << (unsigned)IsNotEqual << E->getSourceRange();
+    << (unsigned)IsRelational << (unsigned)IsNotEqual << E->getSourceRange();
 
   // If the LHS is a plausible entity to assign to, provide a fixit hint to
   // correct common typos.
-  if (CanAssign) {
+  if (!IsRelational && CanAssign) {
     if (IsNotEqual)
       S.Diag(Loc, diag::note_inequality_comparison_to_or_assign)
         << FixItHint::CreateReplacement(Loc, "|=");

test/Sema/unused-expr.c

@@ -7,11 +7,11 @@ double sqrt(double X);  // implicitly const because of no -fmath-errno!
 void bar(volatile int *VP, int *P, int A,
          _Complex double C, volatile _Complex double VC) {
   
-  VP < P;              // expected-warning {{expression result unused}}
+  VP < P;              // expected-warning {{relational comparison result unused}}
   (void)A;
   (void)foo(1,2);      // no warning.
   
-  A < foo(1, 2);       // expected-warning {{expression result unused}}
+  A < foo(1, 2);       // expected-warning {{relational comparison result unused}}
 
   foo(1,2)+foo(4,3);   // expected-warning {{expression result unused}}
 
@@ -54,23 +54,23 @@ void t4(int a) {
   int b = 0;
 
   if (a)
-    b < 1; // expected-warning{{expression result unused}}
+    b < 1; // expected-warning{{relational comparison result unused}}
   else
-    b < 2; // expected-warning{{expression result unused}}
+    b < 2; // expected-warning{{relational comparison result unused}}
     
   while (1)
-    b < 3; // expected-warning{{expression result unused}}
+    b < 3; // expected-warning{{relational comparison result unused}}
 
   do
-    b < 4; // expected-warning{{expression result unused}}
+    b < 4; // expected-warning{{relational comparison result unused}}
   while (1);
   
   for (;;)
-    b < 5; // expected-warning{{expression result unused}}
+    b < 5; // expected-warning{{relational comparison result unused}}
     
-  for (b < 1;;) {} // expected-warning{{expression result unused}}
+  for (b < 1;;) {} // expected-warning{{relational comparison result unused}}
   for (;b < 1;) {}
-  for (;;b < 1) {} // expected-warning{{expression result unused}}
+  for (;;b < 1) {} // expected-warning{{relational comparison result unused}}
 }
 
 // rdar://7186119

test/SemaCXX/MicrosoftExtensions.cpp

@@ -303,7 +303,7 @@ struct SP9 {
   __declspec(property(get=GetV, put=SetV)) T V;
   T GetV() { return 0; }
   void SetV(T v) {}
-  void f() { V = this->V; V < this->V; }
+  bool f() { V = this->V; return V < this->V; }
   void g() { V++; }
   void h() { V*=2; }
 };

test/SemaCXX/warn-unused-comparison.cpp

@@ -3,6 +3,10 @@
 struct A {
   bool operator==(const A&);
   bool operator!=(const A&);
+  bool operator<(const A&);
+  bool operator>(const A&);
+  bool operator<=(const A&);
+  bool operator>=(const A&);
   A operator|=(const A&);
   operator bool();
 };
@@ -15,6 +19,11 @@ void test() {
           // expected-note {{use '=' to turn this equality comparison into an assignment}}
   x != 7; // expected-warning {{inequality comparison result unused}} \
           // expected-note {{use '|=' to turn this inequality comparison into an or-assignment}}
+  x < 7;  // expected-warning {{relational comparison result unused}}
+  x > 7;  // expected-warning {{relational comparison result unused}}
+  x <= 7; // expected-warning {{relational comparison result unused}}
+  x >= 7; // expected-warning {{relational comparison result unused}}
+
   7 == x; // expected-warning {{equality comparison result unused}}
   p == p; // expected-warning {{equality comparison result unused}} \
           // expected-note {{use '=' to turn this equality comparison into an assignment}} \
@@ -25,6 +34,11 @@ void test() {
           // expected-note {{use '=' to turn this equality comparison into an assignment}}
   a != b; // expected-warning {{inequality comparison result unused}} \
           // expected-note {{use '|=' to turn this inequality comparison into an or-assignment}}
+  a < b;  // expected-warning {{relational comparison result unused}}
+  a > b;  // expected-warning {{relational comparison result unused}}
+  a <= b; // expected-warning {{relational comparison result unused}}
+  a >= b; // expected-warning {{relational comparison result unused}}
+
   A() == b; // expected-warning {{equality comparison result unused}}
   if (42) x == 7; // expected-warning {{equality comparison result unused}} \
                   // expected-note {{use '=' to turn this equality comparison into an assignment}}

test/SemaTemplate/resolve-single-template-id.cpp

@@ -67,10 +67,10 @@ int main()
   b = (void (*)()) twoT<int>;
   
   one < one; //expected-warning {{self-comparison always evaluates to false}} \
-             //expected-warning {{expression result unused}}         
+             //expected-warning {{relational comparison result unused}}         
 
   oneT<int> < oneT<int>;  //expected-warning {{self-comparison always evaluates to false}} \
-                          //expected-warning {{expression result unused}}
+                          //expected-warning {{relational comparison result unused}}
 
   two < two; //expected-error 2 {{reference to overloaded function could not be resolved; did you mean to call it with no arguments?}} expected-error {{invalid operands to binary expression ('void' and 'void')}}
   twoT<int> < twoT<int>; //expected-error {{reference to overloaded function could not be resolved; did you mean to call it?}} {{cannot resolve overloaded function 'twoT' from context}}