[clang-tools-extra] [clang-tidy] avoid 64-bit truncation in redundant bitwise checks (PR #201363)

[Daniil Dudkin via cfe-commits]

https://github.com/unterumarmung updated https://github.com/llvm/llvm-project/pull/201363

>From c201e710c4b75832e35f921347c1985f4e834c8f Mon Sep 17 00:00:00 2001
From: Daniil Dudkin <unterumarmung at yandex.ru>
Date: Wed, 3 Jun 2026 16:52:07 +0300
Subject: [PATCH 1/2] [clang-tidy] avoid 64-bit truncation in redundant bitwise
 checks

Fixes #201115
---
 .../misc/RedundantExpressionCheck.cpp         |  6 ++-
 .../checkers/misc/redundant-expression.cpp    | 45 +++++++++++++++++++
 2 files changed, 49 insertions(+), 2 deletions(-)

diff --git a/clang-tools-extra/clang-tidy/misc/RedundantExpressionCheck.cpp b/clang-tools-extra/clang-tidy/misc/RedundantExpressionCheck.cpp
index 9db297990b274..de489da96de3b 100644
--- a/clang-tools-extra/clang-tidy/misc/RedundantExpressionCheck.cpp
+++ b/clang-tools-extra/clang-tidy/misc/RedundantExpressionCheck.cpp
@@ -1178,8 +1178,10 @@ void RedundantExpressionCheck::checkBitwiseExpr(
         !retrieveIntegerConstantExpr(Result, "rhs", RhsValue))
       return;
 
-    const uint64_t LhsConstant = LhsValue.getZExtValue();
-    const uint64_t RhsConstant = RhsValue.getZExtValue();
+    const unsigned ConstantWidth =
+        std::max(LhsValue.getBitWidth(), RhsValue.getBitWidth());
+    const llvm::APInt LhsConstant = LhsValue.extOrTrunc(ConstantWidth);
+    const llvm::APInt RhsConstant = RhsValue.extOrTrunc(ConstantWidth);
     const SourceLocation Loc = ComparisonOperator->getOperatorLoc();
 
     // Check expression: x & k1 == k2  (i.e. x & 0xFF == 0xF00)
diff --git a/clang-tools-extra/test/clang-tidy/checkers/misc/redundant-expression.cpp b/clang-tools-extra/test/clang-tidy/checkers/misc/redundant-expression.cpp
index 4ff0ba867ebb9..4bd2d2df343dc 100644
--- a/clang-tools-extra/test/clang-tidy/checkers/misc/redundant-expression.cpp
+++ b/clang-tools-extra/test/clang-tidy/checkers/misc/redundant-expression.cpp
@@ -572,6 +572,51 @@ int TestBitwise(int X, int Y) {
   return 0;
 }
 
+bool TestBitwiseUInt128(unsigned __int128 Value) {
+  constexpr unsigned __int128 BigBit =
+      static_cast<unsigned __int128>(1) << 100;
+
+  if ((Value & BigBit) == BigBit) return true;
+
+  constexpr unsigned __int128 LowMask = static_cast<unsigned __int128>(0xFF);
+
+  if ((Value & LowMask) == BigBit) return true;
+  // CHECK-MESSAGES: :[[@LINE-1]]:25: warning: logical expression is always false
+  if ((Value & LowMask) != BigBit) return true;
+  // CHECK-MESSAGES: :[[@LINE-1]]:25: warning: logical expression is always true
+  if ((Value | BigBit) == LowMask) return true;
+  // CHECK-MESSAGES: :[[@LINE-1]]:24: warning: logical expression is always false
+  if ((Value | BigBit) != LowMask) return true;
+  // CHECK-MESSAGES: :[[@LINE-1]]:24: warning: logical expression is always true
+
+  return false;
+}
+
+#define UINT128_BIG_BIT (static_cast<unsigned __int128>(1) << 100)
+
+bool TestBitwiseUInt128Macro(unsigned __int128 Value) {
+  return (Value & UINT128_BIG_BIT) == UINT128_BIG_BIT;
+}
+
+template <int N>
+bool TestBitwiseUInt128Template(unsigned __int128 Value) {
+  constexpr unsigned __int128 Mask = static_cast<unsigned __int128>(1) << N;
+  return (Value & Mask) == Mask;
+}
+
+bool UseBitwiseUInt128Template(unsigned __int128 Value) {
+  return TestBitwiseUInt128Template<100>(Value);
+}
+
+using RedundantExpressionU128 = unsigned __int128;
+typedef unsigned __int128 RedundantExpressionTypedefU128;
+
+bool TestBitwiseUInt128AliasCvRef(const RedundantExpressionU128 &Value) {
+  constexpr RedundantExpressionTypedefU128 Mask =
+      static_cast<RedundantExpressionU128>(1) << 100;
+  return (Value & Mask) == Mask;
+}
+
 // Overloaded operators that compare an instance of a struct and an integer
 // constant.
 struct S {

>From ebdf0cdf31eb6909f82ee1ae0e90145ce2bec12c Mon Sep 17 00:00:00 2001
From: Daniil Dudkin <unterumarmung at yandex.ru>
Date: Wed, 3 Jun 2026 16:56:48 +0300
Subject: [PATCH 2/2] add release note

---
 clang-tools-extra/docs/ReleaseNotes.rst | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/clang-tools-extra/docs/ReleaseNotes.rst b/clang-tools-extra/docs/ReleaseNotes.rst
index e6897ebb4cf9f..0617121cb0623 100644
--- a/clang-tools-extra/docs/ReleaseNotes.rst
+++ b/clang-tools-extra/docs/ReleaseNotes.rst
@@ -539,6 +539,10 @@ Changes in existing checks
   <clang-tidy/checks/misc/multiple-inheritance>` by avoiding false positives when
   virtual inheritance causes concrete bases to be counted more than once.
 
+- Improved :doc:`misc-redundant-expression
+  <clang-tidy/checks/misc/redundant-expression>` check by fixing a crash when
+  evaluating bitwise comparisons against integer constants wider than 64 bits.
+
 - Improved :doc:`misc-throw-by-value-catch-by-reference
   <clang-tidy/checks/misc/throw-by-value-catch-by-reference>` check: