[PATCH] D152713: [clang-tidy] Correct sizeof/alignas handling in misc-redundant-expression

[Piotr Zegar via Phabricator via cfe-commits]

PiotrZSL created this revision.
PiotrZSL added reviewers: njames93, carlosgalvezp, Izaron, fwolff.
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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


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D152713

Files:
  clang-tools-extra/clang-tidy/misc/RedundantExpressionCheck.cpp
  clang-tools-extra/docs/ReleaseNotes.rst
  clang-tools-extra/test/clang-tidy/checkers/misc/redundant-expression.cpp


Index: clang-tools-extra/test/clang-tidy/checkers/misc/redundant-expression.cpp
===================================================================
--- clang-tools-extra/test/clang-tidy/checkers/misc/redundant-expression.cpp
+++ clang-tools-extra/test/clang-tidy/checkers/misc/redundant-expression.cpp
@@ -843,3 +843,15 @@
 
   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
+
+}
Index: clang-tools-extra/docs/ReleaseNotes.rst
===================================================================
--- clang-tools-extra/docs/ReleaseNotes.rst
+++ clang-tools-extra/docs/ReleaseNotes.rst
@@ -306,6 +306,10 @@
   <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.
Index: clang-tools-extra/clang-tidy/misc/RedundantExpressionCheck.cpp
===================================================================
--- clang-tools-extra/clang-tidy/misc/RedundantExpressionCheck.cpp
+++ clang-tools-extra/clang-tidy/misc/RedundantExpressionCheck.cpp
@@ -144,8 +144,9 @@
     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());


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