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

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: #63096

Reviewed By: Izaron

Differential Revision: https://reviews.llvm.org/D152713

Author: PiotrZSL

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

@@ -144,8 +144,9 @@ static bool areEquivalentExpr(const Expr *Left, const Expr *Right) {
     const auto *RightUnaryExpr =
         cast<UnaryExprOrTypeTraitExpr>(Right);
     if (LeftUnaryExpr->isArgumentType() && RightUnaryExpr->isArgumentType())
-      return LeftUnaryExpr->getArgumentType() ==
-             RightUnaryExpr->getArgumentType();
+      return LeftUnaryExpr->getKind() == RightUnaryExpr->getKind() &&
+             LeftUnaryExpr->getArgumentType() ==
+                 RightUnaryExpr->getArgumentType();
     if (!LeftUnaryExpr->isArgumentType() && !RightUnaryExpr->isArgumentType())
       return areEquivalentExpr(LeftUnaryExpr->getArgumentExpr(),
                                RightUnaryExpr->getArgumentExpr());

clang-tools-extra/docs/ReleaseNotes.rst

@@ -360,6 +360,10 @@ Changes in existing checks
   <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.

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

@@ -843,3 +843,15 @@ int TestAssignSideEffect(int i) {
 
   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
+
+}