New tautological warning for bitwise-or with non-zero constant always true.

Taking a value and the bitwise-or it with a non-zero constant will always
result in a non-zero value. In a boolean context, this is always true.

if (x | 0x4) {}  // always true, intended '&'

This patch creates a new warning group -Wtautological-bitwise-compare for this
warning. It also moves in the existing tautological bitwise comparisons into
this group. A few other changes were needed to the CFGBuilder so that all bool
contexts would be checked. The warnings in -Wtautological-bitwise-compare will
be off by default due to using the CFG.

Fixes: https://bugs.llvm.org/show_bug.cgi?id=42666
Differential Revision: https://reviews.llvm.org/D66046



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@375318 91177308-0d34-0410-b5e6-96231b3b80d8

3 files changed, 7 insertions, 1 deletions

diff --git a/include/clang/Analysis/CFG.h b/include/clang/Analysis/CFG.h
index b24e32c966..a8301a0e00 100644
--- a/include/clang/Analysis/CFG.h
+++ b/include/clang/Analysis/CFG.h
@@ -1213,6 +1213,7 @@ public:
   virtual void compareAlwaysTrue(const BinaryOperator *B, bool isAlwaysTrue) {}
   virtual void compareBitwiseEquality(const BinaryOperator *B,
                                       bool isAlwaysTrue) {}
+  virtual void compareBitwiseOr(const BinaryOperator *B) {}
 };
 
 /// Represents a source-level, intra-procedural CFG that represents the
diff --git a/include/clang/Basic/DiagnosticGroups.td b/include/clang/Basic/DiagnosticGroups.td
index 396f297881..3573ebdfc6 100644
--- a/include/clang/Basic/DiagnosticGroups.td
+++ b/include/clang/Basic/DiagnosticGroups.td
@@ -516,12 +516,14 @@ def TautologicalConstantCompare : DiagGroup<"tautological-constant-compare",
                                             [TautologicalOutOfRangeCompare]>;
 def TautologicalPointerCompare : DiagGroup<"tautological-pointer-compare">;
 def TautologicalOverlapCompare : DiagGroup<"tautological-overlap-compare">;
+def TautologicalBitwiseCompare : DiagGroup<"tautological-bitwise-compare">;
 def TautologicalUndefinedCompare : DiagGroup<"tautological-undefined-compare">;
 def TautologicalObjCBoolCompare : DiagGroup<"tautological-objc-bool-compare">;
 def TautologicalCompare : DiagGroup<"tautological-compare",
                                     [TautologicalConstantCompare,
                                      TautologicalPointerCompare,
                                      TautologicalOverlapCompare,
+                                     TautologicalBitwiseCompare,
                                      TautologicalUndefinedCompare,
                                      TautologicalObjCBoolCompare]>;
 def HeaderHygiene : DiagGroup<"header-hygiene">;
diff --git a/include/clang/Basic/DiagnosticSemaKinds.td b/include/clang/Basic/DiagnosticSemaKinds.td
index e41cfe2fe7..98fce04e66 100644
--- a/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/include/clang/Basic/DiagnosticSemaKinds.td
@@ -8332,7 +8332,10 @@ def warn_comparison_always : Warning<
   InGroup<TautologicalCompare>;
 def warn_comparison_bitwise_always : Warning<
   "bitwise comparison always evaluates to %select{false|true}0">,
-  InGroup<TautologicalCompare>;
+  InGroup<TautologicalBitwiseCompare>, DefaultIgnore;
+def warn_comparison_bitwise_or : Warning<
+  "bitwise or with non-zero value always evaluates to true">,
+  InGroup<TautologicalBitwiseCompare>, DefaultIgnore;
 def warn_tautological_overlap_comparison : Warning<
   "overlapping comparisons always evaluate to %select{false|true}0">,
   InGroup<TautologicalOverlapCompare>, DefaultIgnore;