From 7afd71e4ff5d13fdea68cd1261a96b19488d39db Mon Sep 17 00:00:00 2001
From: Jordan Rose <jordan_rose@apple.com>
Date: Tue, 20 May 2014 17:31:11 +0000
Subject: Add a check for tautological bitwise comparisons to
 -Wtautological-compare.
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This catches issues like:

if ((x & 8) == 4) { ... }
if ((x | 4) != 3) { ... }

Patch by Anders Rönnholm!

llvm-svn: 209221
---
 clang/lib/Analysis/CFG.cpp | 43 +++++++++++++++++++++++++++++++++++--------
 1 file changed, 35 insertions(+), 8 deletions(-)

(limited to 'clang/lib/Analysis')

diff --git a/clang/lib/Analysis/CFG.cpp b/clang/lib/Analysis/CFG.cpp
index 3139ae4c5d3..5d2926c0f0e 100644
--- a/clang/lib/Analysis/CFG.cpp
+++ b/clang/lib/Analysis/CFG.cpp
@@ -534,9 +534,10 @@ private:
     }
   }
 
-  /// Find a equality comparison with an expression evaluating to a boolean and
-  /// a constant other than 0 and 1.
-  /// e.g. if (!x == 10)
+  /// Find an incorrect equality comparison. Either with an expression
+  /// evaluating to a boolean and a constant other than 0 and 1.
+  /// e.g. if (!x == 10) or a bitwise and/or operation that always evaluates to
+  /// true/false e.q. (x & 8) == 4.
   TryResult checkIncorrectEqualityOperator(const BinaryOperator *B) {
     const Expr *LHSExpr = B->getLHS()->IgnoreParens();
     const Expr *RHSExpr = B->getRHS()->IgnoreParens();
@@ -549,15 +550,41 @@ private:
       BoolExpr = LHSExpr;
     }
 
-    if (!IntLiteral || !BoolExpr->isKnownToHaveBooleanValue())
+    if (!IntLiteral)
       return TryResult();
 
-    llvm::APInt IntValue = IntLiteral->getValue();
-    if ((IntValue == 1) || (IntValue == 0)) {
-      return TryResult();
+    const BinaryOperator *BitOp = dyn_cast<BinaryOperator>(BoolExpr);
+    if (BitOp && (BitOp->getOpcode() == BO_And ||
+                  BitOp->getOpcode() == BO_Or)) {
+      const Expr *LHSExpr2 = BitOp->getLHS()->IgnoreParens();
+      const Expr *RHSExpr2 = BitOp->getRHS()->IgnoreParens();
+
+      const IntegerLiteral *IntLiteral2 = dyn_cast<IntegerLiteral>(LHSExpr2);
+
+      if (!IntLiteral2)
+        IntLiteral2 = dyn_cast<IntegerLiteral>(RHSExpr2);
+
+      if (!IntLiteral2)
+        return TryResult();
+
+      llvm::APInt L1 = IntLiteral->getValue();
+      llvm::APInt L2 = IntLiteral2->getValue();
+      if ((BitOp->getOpcode() == BO_And && (L2 & L1) != L1) ||
+          (BitOp->getOpcode() == BO_Or  && (L2 | L1) != L1)) {
+        if (BuildOpts.Observer)
+          BuildOpts.Observer->compareBitwiseEquality(B,
+                                                     B->getOpcode() != BO_EQ);
+        TryResult(B->getOpcode() != BO_EQ);
+      }
+    } else if (BoolExpr->isKnownToHaveBooleanValue()) {
+      llvm::APInt IntValue = IntLiteral->getValue();
+      if ((IntValue == 1) || (IntValue == 0)) {
+        return TryResult();
+      }
+      return TryResult(B->getOpcode() != BO_EQ);
     }
 
-    return TryResult(B->getOpcode() != BO_EQ);
+    return TryResult();
   }
 
   TryResult analyzeLogicOperatorCondition(BinaryOperatorKind Relation,
-- 
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