[clang-tidy] Correct sizeof/alignas handling in misc-redundant-expression

[PiotrZSL]

Summary

Fixed issue with the comparison of UnaryExprOrTypeTraitExpr
objects in which only the argument type was checked, without
considering the kind of expression. This led to false positives when
using sizeof(x) and alignof(x) expressions, as only the
comparison x = x was performed without checking if sizeof
was equal to alignof.

Fixes: https://github.com/llvm/llvm-project/issues/63096

[PiotrZSL]

Ping

[Izaron]

LGTM! Thank you for the fix!

clang-tools-extra/clang-tidy/misc/RedundantExpressionCheck.cpp

case Stmt::BinaryOperatorClass:
     return cast<BinaryOperator>(Left)->getOpcode() ==
            cast<BinaryOperator>(Right)->getOpcode();
   case Stmt::UnaryExprOrTypeTraitExprClass:
     const auto *LeftUnaryExpr =
         cast<UnaryExprOrTypeTraitExpr>(Left);
     const auto *RightUnaryExpr =
         cast<UnaryExprOrTypeTraitExpr>(Right);
     if (LeftUnaryExpr->isArgumentType() && RightUnaryExpr->isArgumentType())
-      return LeftUnaryExpr->getArgumentType() ==
+      return LeftUnaryExpr->getKind() == RightUnaryExpr->getKind() &&
+             LeftUnaryExpr->getArgumentType() ==
                  RightUnaryExpr->getArgumentType();
     if (!LeftUnaryExpr->isArgumentType() && !RightUnaryExpr->isArgumentType())
       return areEquivalentExpr(LeftUnaryExpr->getArgumentExpr(),
                                RightUnaryExpr->getArgumentExpr());
 
     return false;
   }
 }
 

clang-tools-extra/docs/ReleaseNotes.rst

- Deprecated check-local options `HeaderFileExtensions`
   in :doc:`misc-definitions-in-headers
   <clang-tidy/checks/misc/definitions-in-headers>` check.
   Global options of the same name should be used instead.
 
 - Fixed false positive in :doc:`misc-definitions-in-headers
   <clang-tidy/checks/misc/definitions-in-headers>` to avoid warning on
   declarations inside anonymous namespaces.
 
+- Fixed false-positive in :doc:`misc-redundant-expression
+  <clang-tidy/checks/misc/redundant-expression>` check where expressions like
+  ``alignof`` or ``sizeof`` were incorrectly flagged as identical.
+
 - Improved :doc:`misc-unused-parameters
   <clang-tidy/checks/misc/unused-parameters>` check with new `IgnoreVirtual`
   option to optionally ignore virtual methods.
 
 - Deprecated check-local options `HeaderFileExtensions`
   in :doc:`misc-unused-using-decls
   <clang-tidy/checks/misc/unused-using-decls>` check.
   Global options of the same name should be used instead.

clang-tools-extra/test/clang-tidy/checkers/misc/redundant-expression.cpp

int TestAssignSideEffect(int i) {
   if ((k = k + 1) != 1 || (k = k + 1) != 2)
     return 0;
 
   if ((k = foo(0)) != 1 || (k = foo(0)) != 2)
     return 1;
 
   return 2;
 }
+
+namespace PR63096 {
+
+struct alignas(sizeof(int)) X {
+  int x;
+};
+
+static_assert(alignof(X) == sizeof(X));
+static_assert(sizeof(X) == sizeof(X));
+// CHECK-MESSAGES: :[[@LINE-1]]:25: warning: both sides of operator are equivalent
+
+}