[Sema] Move some stuff into -Wtautological-unsigned-enum-zero-compare

Summary:
As requested by Sam McCall:
> Enums (not new I guess). Typical case: if (enum < 0 || enum > MAX)
> The warning strongly suggests that the enum < 0 check has no effect
> (for enums with nonnegative ranges).
> Clang doesn't seem to optimize such checks out though, and they seem
> likely to catch bugs in some cases. Yes, only if there's UB elsewhere,
> but I assume not optimizing out these checks indicates a deliberate
> decision to stay somewhat compatible with a technically-incorrect
> mental model.
> If this is the case, should we move these to a
> -Wtautological-compare-enum subcategory?

Reviewers: rjmccall, rsmith, aaron.ballman, sammccall, bkramer, djasper

Reviewed By: aaron.ballman

Subscribers: jroelofs, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D37629

llvm-svn: 313677

clang/include/clang/Basic/DiagnosticGroups.td

@@ -429,12 +429,14 @@ def StringPlusInt : DiagGroup<"string-plus-int">;
 def StringPlusChar : DiagGroup<"string-plus-char">;
 def StrncatSize : DiagGroup<"strncat-size">;
 def TautologicalUnsignedZeroCompare : DiagGroup<"tautological-unsigned-zero-compare">;
+def TautologicalUnsignedEnumZeroCompare : DiagGroup<"tautological-unsigned-enum-zero-compare">;
 def TautologicalOutOfRangeCompare : DiagGroup<"tautological-constant-out-of-range-compare">;
 def TautologicalPointerCompare : DiagGroup<"tautological-pointer-compare">;
 def TautologicalOverlapCompare : DiagGroup<"tautological-overlap-compare">;
 def TautologicalUndefinedCompare : DiagGroup<"tautological-undefined-compare">;
 def TautologicalCompare : DiagGroup<"tautological-compare",
                                     [TautologicalUnsignedZeroCompare,
+                                     TautologicalUnsignedEnumZeroCompare,
                                      TautologicalOutOfRangeCompare,
                                      TautologicalPointerCompare,
                                      TautologicalOverlapCompare,

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -5906,19 +5906,26 @@ def note_typecheck_assign_const : Note<
   "member function %q1 is declared const here|"
   "%select{|nested }1data member %2 declared const here}0">;
 
+def warn_lunsigned_always_true_comparison : Warning<
+  "comparison of unsigned expression %0 is always %select{false|true}1">,
+  InGroup<TautologicalUnsignedZeroCompare>;
+def warn_runsigned_always_true_comparison : Warning<
+  "comparison of %0 unsigned expression is always %select{false|true}1">,
+  InGroup<TautologicalUnsignedZeroCompare>;
+def warn_lunsigned_enum_always_true_comparison : Warning<
+  "comparison of unsigned enum expression %0 is always %select{false|true}1">,
+  InGroup<TautologicalUnsignedEnumZeroCompare>;
+def warn_runsigned_enum_always_true_comparison : Warning<
+  "comparison of %0 unsigned enum expression is always %select{false|true}1">,
+  InGroup<TautologicalUnsignedEnumZeroCompare>;
+
 def warn_mixed_sign_comparison : Warning<
   "comparison of integers of different signs: %0 and %1">,
   InGroup<SignCompare>, DefaultIgnore;
-def warn_lunsigned_always_true_comparison : Warning<
-  "comparison of unsigned%select{| enum}2 expression %0 is always %1">,
-  InGroup<TautologicalUnsignedZeroCompare>;
 def warn_out_of_range_compare : Warning<
   "comparison of %select{constant %0|true|false}1 with " 
   "%select{expression of type %2|boolean expression}3 is always "
   "%select{false|true}4">, InGroup<TautologicalOutOfRangeCompare>;
-def warn_runsigned_always_true_comparison : Warning<
-  "comparison of %0 unsigned%select{| enum}2 expression is always %1">,
-  InGroup<TautologicalUnsignedZeroCompare>;
 def warn_comparison_of_mixed_enum_types : Warning<
   "comparison of two values with different enumeration types"
   "%diff{ ($ and $)|}0,1">,

clang/lib/Sema/SemaChecking.cpp

@@ -8583,7 +8583,7 @@ bool CheckTautologicalComparisonWithZero(Sema &S, BinaryOperator *E) {
 
   // bool values are handled by DiagnoseOutOfRangeComparison().
 
-  BinaryOperatorKind op = E->getOpcode();
+  BinaryOperatorKind Op = E->getOpcode();
   if (E->isValueDependent())
     return false;
 
@@ -8592,22 +8592,30 @@ bool CheckTautologicalComparisonWithZero(Sema &S, BinaryOperator *E) {
 
   bool Match = true;
 
-  if (op == BO_LT && isNonBooleanUnsignedValue(LHS) && IsZero(S, RHS)) {
+  if (Op == BO_LT && isNonBooleanUnsignedValue(LHS) && IsZero(S, RHS)) {
-    S.Diag(E->getOperatorLoc(), diag::warn_lunsigned_always_true_comparison)
+    S.Diag(E->getOperatorLoc(),
-      << "< 0" << "false" << HasEnumType(LHS)
+           HasEnumType(LHS) ? diag::warn_lunsigned_enum_always_true_comparison
-      << LHS->getSourceRange() << RHS->getSourceRange();
+                            : diag::warn_lunsigned_always_true_comparison)
-  } else if (op == BO_GE && isNonBooleanUnsignedValue(LHS) && IsZero(S, RHS)) {
+        << "< 0"
-    S.Diag(E->getOperatorLoc(), diag::warn_lunsigned_always_true_comparison)
+        << "false" << LHS->getSourceRange() << RHS->getSourceRange();
-      << ">= 0" << "true" << HasEnumType(LHS)
+  } else if (Op == BO_GE && isNonBooleanUnsignedValue(LHS) && IsZero(S, RHS)) {
-      << LHS->getSourceRange() << RHS->getSourceRange();
+    S.Diag(E->getOperatorLoc(),
-  } else if (op == BO_GT && isNonBooleanUnsignedValue(RHS) && IsZero(S, LHS)) {
+           HasEnumType(LHS) ? diag::warn_lunsigned_enum_always_true_comparison
-    S.Diag(E->getOperatorLoc(), diag::warn_runsigned_always_true_comparison)
+                            : diag::warn_lunsigned_always_true_comparison)
-      << "0 >" << "false" << HasEnumType(RHS)
+        << ">= 0"
-      << LHS->getSourceRange() << RHS->getSourceRange();
+        << "true" << LHS->getSourceRange() << RHS->getSourceRange();
-  } else if (op == BO_LE && isNonBooleanUnsignedValue(RHS) && IsZero(S, LHS)) {
+  } else if (Op == BO_GT && isNonBooleanUnsignedValue(RHS) && IsZero(S, LHS)) {
-    S.Diag(E->getOperatorLoc(), diag::warn_runsigned_always_true_comparison)
+    S.Diag(E->getOperatorLoc(),
-      << "0 <=" << "true" << HasEnumType(RHS)
+           HasEnumType(RHS) ? diag::warn_runsigned_enum_always_true_comparison
-      << LHS->getSourceRange() << RHS->getSourceRange();
+                            : diag::warn_runsigned_always_true_comparison)
+        << "0 >"
+        << "false" << LHS->getSourceRange() << RHS->getSourceRange();
+  } else if (Op == BO_LE && isNonBooleanUnsignedValue(RHS) && IsZero(S, LHS)) {
+    S.Diag(E->getOperatorLoc(),
+           HasEnumType(RHS) ? diag::warn_runsigned_enum_always_true_comparison
+                            : diag::warn_runsigned_always_true_comparison)
+        << "0 <="
+        << "true" << LHS->getSourceRange() << RHS->getSourceRange();
   } else
     Match = false;
 

clang/test/Sema/compare.c

@@ -308,8 +308,59 @@ int rdar8414119_bar(unsigned x) {
 int rdar8511238() {
   enum A { A_foo, A_bar };
   enum A a;
+
+  if (a == 0)
+      return 0;
+  if (a != 0)
+      return 0;
   if (a < 0) // expected-warning {{comparison of unsigned enum expression < 0 is always false}}
-    return 0;
+      return 0;
+  if (a <= 0)
+      return 0;
+  if (a > 0)
+      return 0;
+  if (a >= 0) // expected-warning {{comparison of unsigned enum expression >= 0 is always true}}
+      return 0;
+
+  if (0 == a)
+      return 0;
+  if (0 != a)
+      return 0;
+  if (0 < a)
+      return 0;
+  if (0 <= a) // expected-warning {{comparison of 0 <= unsigned enum expression is always true}}
+      return 0;
+  if (0 > a) // expected-warning {{comparison of 0 > unsigned enum expression is always false}}
+      return 0;
+  if (0 >= a)
+      return 0;
+
+  if (a == 0U)
+      return 0;
+  if (a != 0U)
+      return 0;
+  if (a < 0U) // expected-warning {{comparison of unsigned enum expression < 0 is always false}}
+      return 0;
+  if (a <= 0U)
+      return 0;
+  if (a > 0U)
+      return 0;
+  if (a >= 0U) // expected-warning {{comparison of unsigned enum expression >= 0 is always true}}
+      return 0;
+
+  if (0U == a)
+      return 0;
+  if (0U != a)
+      return 0;
+  if (0U < a)
+      return 0;
+  if (0U <= a) // expected-warning {{comparison of 0 <= unsigned enum expression is always true}}
+      return 0;
+  if (0U > a) // expected-warning {{comparison of 0 > unsigned enum expression is always false}}
+      return 0;
+  if (0U >= a)
+      return 0;
+
   return 20;
 }
 

clang/test/Sema/tautological-unsigned-enum-zero-compare.c

@@ -0,0 +1,46 @@
+// RUN: %clang_cc1 -fsyntax-only -DTEST -verify %s
+// RUN: %clang_cc1 -fsyntax-only -Wno-tautological-unsigned-enum-zero-compare -verify %s
+
+int main() {
+  enum A { A_foo, A_bar };
+  enum A a;
+
+#ifdef TEST
+  if (a < 0) // expected-warning {{comparison of unsigned enum expression < 0 is always false}}
+    return 0;
+  if (a >= 0) // expected-warning {{comparison of unsigned enum expression >= 0 is always true}}
+    return 0;
+  if (0 <= a) // expected-warning {{comparison of 0 <= unsigned enum expression is always true}}
+    return 0;
+  if (0 > a) // expected-warning {{comparison of 0 > unsigned enum expression is always false}}
+    return 0;
+  if (a < 0U) // expected-warning {{comparison of unsigned enum expression < 0 is always false}}
+    return 0;
+  if (a >= 0U) // expected-warning {{comparison of unsigned enum expression >= 0 is always true}}
+    return 0;
+  if (0U <= a) // expected-warning {{comparison of 0 <= unsigned enum expression is always true}}
+    return 0;
+  if (0U > a) // expected-warning {{comparison of 0 > unsigned enum expression is always false}}
+    return 0;
+#else
+  // expected-no-diagnostics
+  if (a < 0)
+    return 0;
+  if (a >= 0)
+    return 0;
+  if (0 <= a)
+    return 0;
+  if (0 > a)
+    return 0;
+  if (a < 0U)
+    return 0;
+  if (a >= 0U)
+    return 0;
+  if (0U <= a)
+    return 0;
+  if (0U > a)
+    return 0;
+#endif
+
+  return 1;
+}