[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

1 files changed, 25 insertions, 17 deletions

diff --git a/clang/lib/Sema/SemaChecking.cpp b/clang/lib/Sema/SemaChecking.cpp
index 212fe65c76f..6544cb923b1 100644
--- a/clang/lib/Sema/SemaChecking.cpp
+++ b/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)) {
-    S.Diag(E->getOperatorLoc(), diag::warn_lunsigned_always_true_comparison)
-      << "< 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(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(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(RHS)
-      << LHS->getSourceRange() << RHS->getSourceRange();
+  if (Op == BO_LT && isNonBooleanUnsignedValue(LHS) && IsZero(S, RHS)) {
+    S.Diag(E->getOperatorLoc(),
+           HasEnumType(LHS) ? diag::warn_lunsigned_enum_always_true_comparison
+                            : diag::warn_lunsigned_always_true_comparison)
+        << "< 0"
+        << "false" << LHS->getSourceRange() << RHS->getSourceRange();
+  } else if (Op == BO_GE && isNonBooleanUnsignedValue(LHS) && IsZero(S, RHS)) {
+    S.Diag(E->getOperatorLoc(),
+           HasEnumType(LHS) ? diag::warn_lunsigned_enum_always_true_comparison
+                            : diag::warn_lunsigned_always_true_comparison)
+        << ">= 0"
+        << "true" << LHS->getSourceRange() << RHS->getSourceRange();
+  } else if (Op == BO_GT && 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 >"
+        << "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;