Index: clang-tools-extra/clang-tidy/bugprone/BugproneTidyModule.cpp
===================================================================
--- clang-tools-extra/clang-tidy/bugprone/BugproneTidyModule.cpp
+++ clang-tools-extra/clang-tidy/bugprone/BugproneTidyModule.cpp
@@ -42,6 +42,7 @@
 #include "StringIntegerAssignmentCheck.h"
 #include "StringLiteralWithEmbeddedNulCheck.h"
 #include "SuspiciousEnumUsageCheck.h"
+#include "SuspiciousMemoryComparisonCheck.h"
 #include "SuspiciousMemsetUsageCheck.h"
 #include "SuspiciousMissingCommaCheck.h"
 #include "SuspiciousSemicolonCheck.h"
@@ -131,6 +132,8 @@
         "bugprone-string-literal-with-embedded-nul");
     CheckFactories.registerCheck<SuspiciousEnumUsageCheck>(
         "bugprone-suspicious-enum-usage");
+    CheckFactories.registerCheck<SuspiciousMemoryComparisonCheck>(
+        "bugprone-suspicious-memory-comparison");
     CheckFactories.registerCheck<SuspiciousMemsetUsageCheck>(
         "bugprone-suspicious-memset-usage");
     CheckFactories.registerCheck<SuspiciousMissingCommaCheck>(
Index: clang-tools-extra/clang-tidy/bugprone/CMakeLists.txt
===================================================================
--- clang-tools-extra/clang-tidy/bugprone/CMakeLists.txt
+++ clang-tools-extra/clang-tidy/bugprone/CMakeLists.txt
@@ -34,6 +34,7 @@
   StringIntegerAssignmentCheck.cpp
   StringLiteralWithEmbeddedNulCheck.cpp
   SuspiciousEnumUsageCheck.cpp
+  SuspiciousMemoryComparisonCheck.cpp
   SuspiciousMemsetUsageCheck.cpp
   SuspiciousMissingCommaCheck.cpp
   SuspiciousSemicolonCheck.cpp
Index: clang-tools-extra/clang-tidy/bugprone/SuspiciousMemoryComparisonCheck.h
===================================================================
--- /dev/null
+++ clang-tools-extra/clang-tidy/bugprone/SuspiciousMemoryComparisonCheck.h
@@ -0,0 +1,35 @@
+//===--- SuspiciousMemoryComparisonCheck.h - clang-tidy ---------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_BUGPRONE_SUSPICIOUSMEMORYCOMPARISONCHECK_H
+#define LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_BUGPRONE_SUSPICIOUSMEMORYCOMPARISONCHECK_H
+
+#include "../ClangTidyCheck.h"
+
+namespace clang {
+namespace tidy {
+namespace bugprone {
+
+/// Finds potentially incorrect calls to ``memcmp()`` that compare padding or
+/// non-standard-layout classes.
+///
+/// For the user-facing documentation see:
+/// http://clang.llvm.org/extra/clang-tidy/checks/bugprone-suspicious-memory-comparison.html
+class SuspiciousMemoryComparisonCheck : public ClangTidyCheck {
+public:
+  SuspiciousMemoryComparisonCheck(StringRef Name, ClangTidyContext *Context)
+      : ClangTidyCheck(Name, Context) {}
+  void registerMatchers(ast_matchers::MatchFinder *Finder) override;
+  void check(const ast_matchers::MatchFinder::MatchResult &Result) override;
+};
+
+} // namespace bugprone
+} // namespace tidy
+} // namespace clang
+
+#endif // LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_BUGPRONE_SUSPICIOUSMEMORYCOMPARISONCHECK_H
Index: clang-tools-extra/clang-tidy/bugprone/SuspiciousMemoryComparisonCheck.cpp
===================================================================
--- /dev/null
+++ clang-tools-extra/clang-tidy/bugprone/SuspiciousMemoryComparisonCheck.cpp
@@ -0,0 +1,158 @@
+//===--- SuspiciousMemoryComparisonCheck.cpp - clang-tidy -----------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "SuspiciousMemoryComparisonCheck.h"
+#include "clang/AST/ASTContext.h"
+#include "clang/ASTMatchers/ASTMatchFinder.h"
+
+using namespace clang::ast_matchers;
+
+namespace clang {
+namespace tidy {
+namespace bugprone {
+
+static bool hasPadding(const ASTContext &Ctx, const RecordDecl *RD,
+                       uint64_t ComparedBits);
+
+static uint64_t getFieldSize(const FieldDecl &FD, QualType FieldType,
+                             const ASTContext &Ctx) {
+  return FD.isBitField() ? FD.getBitWidthValue(Ctx)
+                         : Ctx.getTypeSize(FieldType);
+}
+
+static bool hasPaddingInBase(const ASTContext &Ctx, const RecordDecl *RD,
+                             uint64_t ComparedBits, uint64_t &TotalSize) {
+  auto IsNotEmptyBase = [](const CXXBaseSpecifier &Base) {
+    return !Base.getType()->getAsCXXRecordDecl()->isEmpty();
+  };
+
+  if (const auto *CXXRD = dyn_cast<CXXRecordDecl>(RD)) {
+    auto NonEmptyBaseIt = llvm::find_if(CXXRD->bases(), IsNotEmptyBase);
+    if (NonEmptyBaseIt != CXXRD->bases().end()) {
+      assert(llvm::count_if(CXXRD->bases(), IsNotEmptyBase) == 1 &&
+             "RD is expected to be a standard layout type");
+
+      const CXXRecordDecl *BaseRD =
+          NonEmptyBaseIt->getType()->getAsCXXRecordDecl();
+      uint64_t SizeOfBase = Ctx.getTypeSize(BaseRD->getTypeForDecl());
+      TotalSize += SizeOfBase;
+
+      // Check if comparing padding in base.
+      if (hasPadding(Ctx, BaseRD, ComparedBits))
+        return true;
+    }
+  }
+
+  return false;
+}
+
+static bool hasPaddingBetweenFields(const ASTContext &Ctx, const RecordDecl *RD,
+                                    uint64_t ComparedBits,
+                                    uint64_t &TotalSize) {
+  for (const auto &Field : RD->fields()) {
+    uint64_t FieldOffset = Ctx.getFieldOffset(Field);
+
+    // Check if comparing padding before this field.
+    if (FieldOffset > TotalSize && TotalSize < ComparedBits)
+      return true;
+
+    if (FieldOffset >= ComparedBits)
+      return false;
+
+    if (!Field->isZeroSize(Ctx)) {
+      uint64_t SizeOfField = getFieldSize(*Field, Field->getType(), Ctx);
+      TotalSize += SizeOfField;
+
+      // Check if comparing padding in nested record.
+      if (Field->getType()->isRecordType() &&
+          hasPadding(Ctx, Field->getType()->getAsRecordDecl()->getDefinition(),
+                     ComparedBits - FieldOffset))
+        return true;
+    }
+  }
+
+  return false;
+}
+
+static bool hasPadding(const ASTContext &Ctx, const RecordDecl *RD,
+                       uint64_t ComparedBits) {
+  assert(RD && RD->isCompleteDefinition() &&
+         "Expected the complete record definition.");
+  if (RD->isUnion())
+    return false;
+
+  uint64_t TotalSize = 0;
+
+  if (hasPaddingInBase(Ctx, RD, ComparedBits, TotalSize) ||
+      hasPaddingBetweenFields(Ctx, RD, ComparedBits, TotalSize))
+    return true;
+
+  // Check if comparing trailing padding.
+  return TotalSize < Ctx.getTypeSize(RD->getTypeForDecl()) &&
+         ComparedBits > TotalSize;
+}
+
+static llvm::Optional<int64_t> tryEvaluateSizeExpr(const Expr *SizeExpr,
+                                                   const ASTContext &Ctx) {
+  Expr::EvalResult Result;
+  if (SizeExpr->EvaluateAsRValue(Result, Ctx))
+    return Ctx.toBits(
+        CharUnits::fromQuantity(Result.Val.getInt().getExtValue()));
+  return None;
+}
+
+void SuspiciousMemoryComparisonCheck::registerMatchers(MatchFinder *Finder) {
+  Finder->addMatcher(
+      callExpr(callee(namedDecl(
+                   anyOf(hasName("::memcmp"), hasName("::std::memcmp")))))
+          .bind("call"),
+      this);
+}
+
+void SuspiciousMemoryComparisonCheck::check(
+    const MatchFinder::MatchResult &Result) {
+  const ASTContext &Ctx = *Result.Context;
+  const auto *CE = Result.Nodes.getNodeAs<CallExpr>("call");
+
+  const Expr *SizeExpr = CE->getArg(2);
+  assert(SizeExpr != nullptr && "Third argument of memcmp is mandatory.");
+  llvm::Optional<int64_t> ComparedBits = tryEvaluateSizeExpr(SizeExpr, Ctx);
+
+  for (unsigned int i = 0; i < 2; ++i) {
+    const Expr *ArgExpr = CE->getArg(i);
+    QualType ArgType = ArgExpr->IgnoreImplicit()->getType();
+    const Type *PointeeType = ArgType->getPointeeOrArrayElementType();
+    assert(PointeeType != nullptr && "PointeeType should always be available.");
+
+    if (PointeeType->isRecordType()) {
+      if (const RecordDecl *RD =
+              PointeeType->getAsRecordDecl()->getDefinition()) {
+        if (const auto *CXXDecl = dyn_cast<CXXRecordDecl>(RD)) {
+          if (!CXXDecl->isStandardLayout()) {
+            diag(CE->getBeginLoc(),
+                 "comparing object representation of non-standard-layout "
+                 "type %0; consider using a comparison operator instead")
+                << PointeeType->getAsTagDecl();
+            break;
+          }
+        }
+
+        if (ComparedBits && hasPadding(Ctx, RD, *ComparedBits)) {
+          diag(CE->getBeginLoc(), "comparing padding data in type %0; "
+                                  "consider comparing the fields manually")
+              << PointeeType->getAsTagDecl();
+          break;
+        }
+      }
+    }
+  }
+}
+
+} // namespace bugprone
+} // namespace tidy
+} // namespace clang
Index: clang-tools-extra/clang-tidy/cert/CERTTidyModule.cpp
===================================================================
--- clang-tools-extra/clang-tidy/cert/CERTTidyModule.cpp
+++ clang-tools-extra/clang-tidy/cert/CERTTidyModule.cpp
@@ -11,6 +11,7 @@
 #include "../ClangTidyModuleRegistry.h"
 #include "../bugprone/UnhandledSelfAssignmentCheck.h"
 #include "../bugprone/BadSignalToKillThreadCheck.h"
+#include "../bugprone/SuspiciousMemoryComparisonCheck.h"
 #include "../google/UnnamedNamespaceInHeaderCheck.h"
 #include "../misc/NewDeleteOverloadsCheck.h"
 #include "../misc/NonCopyableObjects.h"
@@ -80,6 +81,9 @@
         "cert-dcl16-c");
     // ENV
     CheckFactories.registerCheck<CommandProcessorCheck>("cert-env33-c");
+    // EXP
+    CheckFactories.registerCheck<bugprone::SuspiciousMemoryComparisonCheck>(
+        "cert-exp42-c");
     // FLP
     CheckFactories.registerCheck<FloatLoopCounter>("cert-flp30-c");
     // FIO
Index: clang-tools-extra/docs/ReleaseNotes.rst
===================================================================
--- clang-tools-extra/docs/ReleaseNotes.rst
+++ clang-tools-extra/docs/ReleaseNotes.rst
@@ -94,6 +94,12 @@
   Without the null terminator it can result in undefined behaviour when the
   string is read.
 
+- New :doc:`bugprone-suspicious-memory-comparison
+  <clang-tidy/checks/bugprone-suspicious-memory-comparison>` check.
+
+  Finds potentially incorrect calls to ``memcmp()`` that compare padding or
+  non-standard-layout classes.
+
 - New :doc:`cert-mem57-cpp
   <clang-tidy/checks/cert-mem57-cpp>` check.
 
@@ -160,6 +166,11 @@
   Finds types that could be made trivially-destructible by removing out-of-line
   defaulted destructor declarations.
 
+- New alias :doc:`cert-exp42-c
+  <clang-tidy/checks/cert-exp42-c>` to
+  :doc:`bugprone-suspicious-memory-comparison
+  <clang-tidy/checks/bugprone-suspicious-memory-comparison>` was added.
+
 - Improved :doc:`bugprone-posix-return
   <clang-tidy/checks/bugprone-posix-return>` check.
 
Index: clang-tools-extra/docs/clang-tidy/checks/bugprone-suspicious-memory-comparison.rst
===================================================================
--- /dev/null
+++ clang-tools-extra/docs/clang-tidy/checks/bugprone-suspicious-memory-comparison.rst
@@ -0,0 +1,14 @@
+.. title:: clang-tidy - bugprone-suspicious-memory-comparison
+
+bugprone-suspicious-memory-comparison
+=====================================
+
+Finds potentially incorrect calls to ``memcmp()`` that compare padding or
+non-standard-layout classes.
+
+This check corresponds to the CERT C Coding Standard rule
+`EXP42-C. Do not compare padding data
+<https://wiki.sei.cmu.edu/confluence/display/c/EXP42-C.+Do+not+compare+padding+data>`_.
+and part of the CERT C++ Coding Standard rule
+`OOP57-CPP. Prefer special member functions and overloaded operators to C Standard Library functions
+<https://wiki.sei.cmu.edu/confluence/display/cplusplus/OOP57-CPP.+Prefer+special+member+functions+and+overloaded+operators+to+C+Standard+Library+functions>`_.
Index: clang-tools-extra/docs/clang-tidy/checks/cert-exp42-c.rst
===================================================================
--- /dev/null
+++ clang-tools-extra/docs/clang-tidy/checks/cert-exp42-c.rst
@@ -0,0 +1,9 @@
+.. title:: clang-tidy - cert-exp42-c
+.. meta::
+   :http-equiv=refresh: 5;URL=bugprone-suspicious-memory-comparison.html
+
+cert-exp42-c
+============
+
+The cert-exp42-c check is an alias, please see
+`bugprone-suspicious-memory-comparison <bugprone-suspicious-memory-comparison.html>`_ for more information.
Index: clang-tools-extra/docs/clang-tidy/checks/list.rst
===================================================================
--- clang-tools-extra/docs/clang-tidy/checks/list.rst
+++ clang-tools-extra/docs/clang-tidy/checks/list.rst
@@ -72,6 +72,7 @@
    `bugprone-string-integer-assignment <bugprone-string-integer-assignment.html>`_, "Yes"
    `bugprone-string-literal-with-embedded-nul <bugprone-string-literal-with-embedded-nul.html>`_,
    `bugprone-suspicious-enum-usage <bugprone-suspicious-enum-usage.html>`_,
+   `bugprone-suspicious-memory-comparison <bugprone-suspicious-memory-comparison.html>`_,
    `bugprone-suspicious-memset-usage <bugprone-suspicious-memset-usage.html>`_, "Yes"
    `bugprone-suspicious-missing-comma <bugprone-suspicious-missing-comma.html>`_,
    `bugprone-suspicious-semicolon <bugprone-suspicious-semicolon.html>`_, "Yes"
@@ -294,6 +295,7 @@
    `cert-dcl59-cpp <cert-dcl59-cpp.html>`_, `google-build-namespaces <google-build-namespaces.html>`_,
    `cert-err09-cpp <cert-err09-cpp.html>`_, `misc-throw-by-value-catch-by-reference <misc-throw-by-value-catch-by-reference.html>`_,
    `cert-err61-cpp <cert-err61-cpp.html>`_, `misc-throw-by-value-catch-by-reference <misc-throw-by-value-catch-by-reference.html>`_,
+   `cert-exp42-c <cert-exp42-c.html>`_, `bugprone-suspicious-memory-comparison <bugprone-suspicious-memory-comparison.html>`_,
    `cert-fio38-c <cert-fio38-c.html>`_, `misc-non-copyable-objects <misc-non-copyable-objects.html>`_,
    `cert-msc30-c <cert-msc30-c.html>`_, `cert-msc50-cpp <cert-msc50-cpp.html>`_,
    `cert-msc32-c <cert-msc32-c.html>`_, `cert-msc51-cpp <cert-msc51-cpp.html>`_,
Index: clang-tools-extra/test/clang-tidy/checkers/bugprone-suspicious-memory-comparison-32bits.cpp
===================================================================
--- /dev/null
+++ clang-tools-extra/test/clang-tidy/checkers/bugprone-suspicious-memory-comparison-32bits.cpp
@@ -0,0 +1,34 @@
+// RUN: %check_clang_tidy %s bugprone-suspicious-memory-comparison %t \
+// RUN: -- -- -target x86_64-unknown-unknown -m32
+
+static_assert(sizeof(int *) == sizeof(int));
+
+namespace std {
+typedef __SIZE_TYPE__ size_t;
+int memcmp(const void *lhs, const void *rhs, size_t count);
+} // namespace std
+
+namespace no_padding_on_32bit {
+struct S {
+  int x;
+  int *y;
+};
+
+void test() {
+  S a, b;
+  std::memcmp(&a, &b, sizeof(S));
+}
+} // namespace no_padding_on_32bit
+
+namespace inner_padding {
+struct S {
+  char x;
+  int y;
+};
+void test() {
+  S a, b;
+  std::memcmp(&a, &b, sizeof(S));
+  // CHECK-MESSAGES: :[[@LINE-1]]:3: warning: comparing padding data in type
+  // inner_padding::S; consider comparing the fields manually
+}
+} // namespace inner_padding
Index: clang-tools-extra/test/clang-tidy/checkers/bugprone-suspicious-memory-comparison.c
===================================================================
--- /dev/null
+++ clang-tools-extra/test/clang-tidy/checkers/bugprone-suspicious-memory-comparison.c
@@ -0,0 +1,224 @@
+// RUN: %check_clang_tidy %s bugprone-suspicious-memory-comparison %t \
+// RUN: -- -- -target x86_64-unknown-unknown -std=c99
+
+typedef __SIZE_TYPE__ size_t;
+int memcmp(const void *lhs, const void *rhs, size_t count);
+
+// Examples from cert rule exp42-c
+
+struct S {
+  char c;
+  int i;
+  char buffer[13];
+};
+
+void noncompliant(const struct S *left, const struct S *right) {
+  if ((left && right) && (0 == memcmp(left, right, sizeof(struct S)))) {
+    // CHECK-MESSAGES: :[[@LINE-1]]:32: warning: comparing padding data in type
+    // S; consider comparing the fields manually
+  }
+}
+
+void compliant(const struct S *left, const struct S *right) {
+  if ((left && right) && (left->c == right->c) && (left->i == right->i) &&
+      (0 == memcmp(left->buffer, right->buffer, 13))) {
+  }
+}
+
+#pragma pack(push, 1)
+struct Packed_S {
+  char c;
+  int i;
+  char buffer[13];
+};
+#pragma pack(pop)
+
+void compliant_packed(const struct Packed_S *left,
+                      const struct Packed_S *right) {
+  if ((left && right) && (0 == memcmp(left, right, sizeof(struct Packed_S)))) {
+    // no-warning
+  }
+}
+
+struct PredeclaredType;
+
+void Test_PredeclaredType(const struct PredeclaredType *lhs,
+                          const struct PredeclaredType *rhs) {
+  memcmp(lhs, rhs, 1); // no-warning: predeclared type
+}
+
+struct NoPadding {
+  int x;
+  int y;
+};
+
+void Test_NoPadding() {
+  struct NoPadding a, b;
+  memcmp(&a, &b, sizeof(struct NoPadding));
+}
+
+void TestArray_NoPadding() {
+  struct NoPadding a[3], b[3];
+  memcmp(a, b, 3 * sizeof(struct NoPadding));
+}
+
+struct TrailingPadding {
+  int i;
+  char c;
+};
+
+void Test_TrailingPadding() {
+  struct TrailingPadding a, b;
+  memcmp(&a, &b, sizeof(struct TrailingPadding));
+  // CHECK-MESSAGES: :[[@LINE-1]]:3: warning: comparing padding data in type
+  // TrailingPadding; consider comparing the fields manually
+  memcmp(&a, &b, sizeof(int));
+  memcmp(&a, &b, sizeof(int) + sizeof(char));
+  memcmp(&a, &b, 2 * sizeof(int));
+  // CHECK-MESSAGES: :[[@LINE-1]]:3: warning: comparing padding data in type
+  // TrailingPadding; consider comparing the fields manually
+}
+
+void Test_UnknownCount(size_t count) {
+  struct TrailingPadding a, b;
+  memcmp(&a, &b, count); // no-warning: unknown count value
+}
+
+void TestArray_TrailingPadding() {
+  struct TrailingPadding a[3], b[3];
+  memcmp(a, b, 3 * sizeof(struct TrailingPadding));
+  // CHECK-MESSAGES: :[[@LINE-1]]:3: warning: comparing padding data in type
+  // TrailingPadding; consider comparing the fields manually
+}
+
+struct InnerPadding {
+  char c;
+  int i;
+};
+
+void Test_InnerPadding() {
+  struct InnerPadding a, b;
+  memcmp(&a, &b, sizeof(struct InnerPadding));
+  // CHECK-MESSAGES: :[[@LINE-1]]:3: warning: comparing padding data in type
+  // InnerPadding; consider comparing the fields manually
+  memcmp(&a, &b, sizeof(char) + sizeof(int));
+  // CHECK-MESSAGES: :[[@LINE-1]]:3: warning: comparing padding data in type
+  // InnerPadding; consider comparing the fields manually
+  memcmp(&a, &b, sizeof(char));
+  memcmp(&a, &b, 2 * sizeof(char));
+  // CHECK-MESSAGES: :[[@LINE-1]]:3: warning: comparing padding data in type
+  // InnerPadding; consider comparing the fields manually
+}
+
+struct Bitfield_TrailingPaddingBytes {
+  int x : 10;
+  int y : 6;
+};
+
+void Test_Bitfield_TrailingPaddingBytes() {
+  struct Bitfield_TrailingPaddingBytes a, b;
+  memcmp(&a, &b, sizeof(struct S));
+  // CHECK-MESSAGES: :[[@LINE-1]]:3: warning: comparing padding data in type
+  // Bitfield_TrailingPaddingBytes; consider comparing the fields manually
+  memcmp(&a, &b, 2); // no-warning: no padding in first 2 bytes
+}
+
+struct Bitfield_TrailingPaddingBits {
+  int x : 10;
+  int y : 7;
+};
+
+void Test_Bitfield_TrailingPaddingBits() {
+  struct Bitfield_TrailingPaddingBits a, b;
+  memcmp(&a, &b, sizeof(struct Bitfield_TrailingPaddingBits));
+  // CHECK-MESSAGES: :[[@LINE-1]]:3: warning: comparing padding data in type
+  // Bitfield_TrailingPaddingBits; consider comparing the fields manually
+  memcmp(&a, &b, 2);
+  memcmp(&a, &b, 3);
+  // CHECK-MESSAGES: :[[@LINE-1]]:3: warning: comparing padding data in type
+  // Bitfield_TrailingPaddingBits; consider comparing the fields manually
+}
+
+struct Bitfield_InnerPaddingBits {
+  int x : 2;
+  int : 0;
+  int y : 6;
+};
+
+void Test_Bitfield_InnerPaddingBits() {
+  struct Bitfield_InnerPaddingBits a, b;
+  memcmp(&a, &b, 1);
+  // CHECK-MESSAGES: :[[@LINE-1]]:3: warning: comparing padding data in type
+  // Bitfield_InnerPaddingBits; consider comparing the fields manually
+}
+
+struct PaddingAfterUnion {
+  union {
+    char c;
+    short s;
+  } x;
+
+  int y;
+};
+
+void Test_PaddingAfterUnion() {
+  struct PaddingAfterUnion a, b;
+  memcmp(&a, &b, sizeof(short));
+  memcmp(&a, &b, sizeof(int));
+  // CHECK-MESSAGES: :[[@LINE-1]]:3: warning: comparing padding data in type
+  // PaddingAfterUnion; consider comparing the fields manually
+  memcmp(&a, &b, sizeof(struct PaddingAfterUnion));
+  // CHECK-MESSAGES: :[[@LINE-1]]:3: warning: comparing padding data in type
+  // PaddingAfterUnion; consider comparing the fields manually
+}
+
+struct Union_NoPadding {
+  union {
+    int a;
+    char b;
+  } x;
+
+  int y;
+};
+
+void Test_Union_NoPadding() {
+  struct Union_NoPadding a, b;
+  memcmp(&a, &b, 2 * sizeof(int));
+  memcmp(&a, &b, sizeof(struct Union_NoPadding));
+}
+
+struct PaddingInNested {
+  struct TrailingPadding x;
+  char y;
+};
+
+void Test_PaddingInNested() {
+  struct PaddingInNested a, b;
+  memcmp(&a, &b, sizeof(int) + sizeof(char));
+  memcmp(&a, &b, sizeof(int) + 2 * sizeof(char));
+  // CHECK-MESSAGES: :[[@LINE-1]]:3: warning: comparing padding data in type
+  // PaddingInNested; consider comparing the fields manually
+  memcmp(&a, &b, sizeof(struct TrailingPadding));
+  // CHECK-MESSAGES: :[[@LINE-1]]:3: warning: comparing padding data in type
+  // PaddingInNested; consider comparing the fields manually
+  memcmp(&a, &b, sizeof(struct PaddingInNested));
+  // CHECK-MESSAGES: :[[@LINE-1]]:3: warning: comparing padding data in type
+  // PaddingInNested; consider comparing the fields manually
+}
+
+struct PaddingAfterNested {
+  struct {
+    char a;
+    char b;
+  } x;
+  int y;
+};
+
+void Test_PaddingAfterNested() {
+  struct PaddingAfterNested a, b;
+  memcmp(&a, &b, 2 * sizeof(char));
+  memcmp(&a, &b, sizeof(a.x));
+  memcmp(&a, &b, sizeof(struct PaddingAfterNested));
+  // CHECK-MESSAGES: :[[@LINE-1]]:3: warning: comparing padding data in type
+  // PaddingAfterNested; consider comparing the fields manually
+}
Index: clang-tools-extra/test/clang-tidy/checkers/bugprone-suspicious-memory-comparison.cpp
===================================================================
--- /dev/null
+++ clang-tools-extra/test/clang-tidy/checkers/bugprone-suspicious-memory-comparison.cpp
@@ -0,0 +1,228 @@
+// RUN: %check_clang_tidy %s bugprone-suspicious-memory-comparison %t \
+// RUN: -- -- -target x86_64-unknown-unknown
+
+namespace std {
+typedef __SIZE_TYPE__ size_t;
+int memcmp(const void *lhs, const void *rhs, size_t count);
+} // namespace std
+
+namespace sei_cert_example_oop57_cpp {
+class C {
+  int i;
+
+public:
+  virtual void f();
+};
+
+void f(C &c1, C &c2) {
+  if (!std::memcmp(&c1, &c2, sizeof(C))) {
+    // CHECK-MESSAGES: :[[@LINE-1]]:8: warning: comparing object representation
+    // of non-standard-layout type sei_cert_example_oop57_cpp::C; consider
+    // using a comparison operator instead
+  }
+}
+} // namespace sei_cert_example_oop57_cpp
+
+namespace inner_padding_64bit_only {
+struct S {
+  int x;
+  int *y;
+};
+
+void test() {
+  S a, b;
+  std::memcmp(&a, &b, sizeof(S));
+  // CHECK-MESSAGES: :[[@LINE-1]]:3: warning: comparing padding data in type
+  // inner_padding_64bit_only::S; consider comparing the fields manually
+}
+} // namespace inner_padding_64bit_only
+
+namespace padding_in_base {
+class Base {
+  char c;
+  int i;
+};
+
+class Derived : public Base {};
+
+class Derived2 : public Derived {};
+
+void testDerived() {
+  Derived a, b;
+  std::memcmp(&a, &b, sizeof(char));
+  std::memcmp(&a, &b, sizeof(Base));
+  // CHECK-MESSAGES: :[[@LINE-1]]:3: warning: comparing padding data in type
+  // padding_in_base::Derived; consider comparing the fields manually
+  std::memcmp(&a, &b, sizeof(Derived));
+  // CHECK-MESSAGES: :[[@LINE-1]]:3: warning: comparing padding data in type
+  // padding_in_base::Derived; consider comparing the fields manually
+}
+
+void testDerived2() {
+  Derived2 a, b;
+  std::memcmp(&a, &b, sizeof(char));
+  std::memcmp(&a, &b, sizeof(Base));
+  // CHECK-MESSAGES: :[[@LINE-1]]:3: warning: comparing padding data in type
+  // padding_in_base::Derived2; consider comparing the fields manually
+  std::memcmp(&a, &b, sizeof(Derived2));
+  // CHECK-MESSAGES: :[[@LINE-1]]:3: warning: comparing padding data in type
+  // padding_in_base::Derived2; consider comparing the fields manually
+}
+
+} // namespace padding_in_base
+
+namespace no_padding_in_base {
+class Base {
+  int a, b;
+};
+
+class Derived : public Base {};
+
+class Derived2 : public Derived {};
+
+void testDerived() {
+  Derived a, b;
+  std::memcmp(&a, &b, sizeof(Base));
+  std::memcmp(&a, &b, sizeof(Derived));
+}
+
+void testDerived2() {
+  Derived2 a, b;
+  std::memcmp(&a, &b, sizeof(char));
+  std::memcmp(&a, &b, sizeof(Base));
+  std::memcmp(&a, &b, sizeof(Derived2));
+}
+} // namespace no_padding_in_base
+
+namespace non_standard_layout {
+class C {
+private:
+  int x;
+
+public:
+  int y;
+};
+
+void test() {
+  C a, b;
+  std::memcmp(&a, &b, sizeof(C));
+  // CHECK-MESSAGES: :[[@LINE-1]]:3: warning: comparing object representation
+  // of non-standard-layout type non_standard_layout::C; consider using a
+  // comparison operator instead
+}
+
+} // namespace non_standard_layout
+
+namespace static_ignored {
+struct S {
+  static char c;
+  int i;
+};
+
+void test() {
+  S a, b;
+  std::memcmp(&a, &b, sizeof(S));
+}
+} // namespace static_ignored
+
+namespace operator_void_ptr {
+struct S {
+  operator void *() const;
+};
+
+void test() {
+  S s;
+  std::memcmp(s, s, sizeof(s));
+}
+} // namespace operator_void_ptr
+
+namespace empty_struct {
+struct S {};
+
+void test() {
+  S a, b;
+  std::memcmp(&a, &b, sizeof(S));
+  // CHECK-MESSAGES: :[[@LINE-1]]:3: warning: comparing padding data in type
+  // empty_struct::S; consider comparing the fields manually
+}
+} // namespace empty_struct
+
+namespace empty_field {
+struct Empty {};
+struct S {
+  Empty e;
+};
+
+void test() {
+  S a, b;
+  std::memcmp(&a, &b, sizeof(S));
+  // CHECK-MESSAGES: :[[@LINE-1]]:3: warning: comparing padding data in type
+  // empty_field::S; consider comparing the fields manually
+}
+} // namespace empty_field
+
+namespace no_unique_address_attribute {
+struct Empty {};
+
+namespace no_padding {
+struct S {
+  char c;
+  [[no_unique_address]] Empty e;
+};
+
+void test() {
+  S a, b;
+  std::memcmp(&a, &b, sizeof(S));
+}
+
+} // namespace no_padding
+
+namespace multiple_empties_same_type {
+struct S {
+  char c;
+  [[no_unique_address]] Empty e1, e2;
+};
+
+void test() {
+  S a, b;
+  std::memcmp(&a, &b, sizeof(S));
+  // CHECK-MESSAGES: :[[@LINE-1]]:3: warning: comparing padding data in type
+  // no_unique_address_attribute::multiple_empties_same_type::S; consider
+  // comparing the fields manually
+}
+
+} // namespace multiple_empties_same_type
+
+namespace multiple_empties_different_types {
+struct Empty2 {};
+
+struct S {
+  char c;
+  [[no_unique_address]] Empty e1;
+  [[no_unique_address]] Empty2 e2;
+};
+
+void test() {
+  S a, b;
+  std::memcmp(&a, &b, sizeof(S));
+}
+} // namespace multiple_empties_different_types
+} // namespace no_unique_address_attribute
+
+namespace alignment {
+struct S {
+  char x;
+  alignas(sizeof(int)) char y[sizeof(int)];
+};
+
+void test() {
+  S a, b;
+  std::memcmp(&a, &b, sizeof(char));
+  std::memcmp(&a, &b, 2 * sizeof(char));
+  // CHECK-MESSAGES: :[[@LINE-1]]:3: warning: comparing padding data in type
+  // alignment::S; consider comparing the fields manually
+  std::memcmp(&a, &b, sizeof(S));
+  // CHECK-MESSAGES: :[[@LINE-1]]:3: warning: comparing padding data in type
+  // alignment::S; consider comparing the fields manually
+}
+} // namespace alignment