[clang-tidy] Add a checker for zero-length memset.

If there's memset(x, y, 0) in the code it's most likely a mistake. The
checker suggests a fix-it to swap 'y' and '0'.

I think this has the potential to be promoted into a general clang warning
after some testing in clang-tidy.

Differential Revision: http://reviews.llvm.org/D4535

llvm-svn: 213155

5 files changed, 176 insertions, 0 deletions

diff --git a/clang-tools-extra/clang-tidy/google/CMakeLists.txt b/clang-tools-extra/clang-tidy/google/CMakeLists.txt
index 725a4179be7..603df91f10b 100644
--- a/clang-tools-extra/clang-tidy/google/CMakeLists.txt
+++ b/clang-tools-extra/clang-tidy/google/CMakeLists.txt
@@ -5,6 +5,7 @@ add_clang_library(clangTidyGoogleModule
   ExplicitConstructorCheck.cpp
   ExplicitMakePairCheck.cpp
   GoogleTidyModule.cpp
+  MemsetZeroLengthCheck.cpp
   NamedParameterCheck.cpp
   OverloadedUnaryAndCheck.cpp
   StringReferenceMemberCheck.cpp
diff --git a/clang-tools-extra/clang-tidy/google/GoogleTidyModule.cpp b/clang-tools-extra/clang-tidy/google/GoogleTidyModule.cpp
index 416f48d1fa3..1681727061c 100644
--- a/clang-tools-extra/clang-tidy/google/GoogleTidyModule.cpp
+++ b/clang-tools-extra/clang-tidy/google/GoogleTidyModule.cpp
@@ -13,6 +13,7 @@
 #include "AvoidCStyleCastsCheck.h"
 #include "ExplicitConstructorCheck.h"
 #include "ExplicitMakePairCheck.h"
+#include "MemsetZeroLengthCheck.h"
 #include "NamedParameterCheck.h"
 #include "OverloadedUnaryAndCheck.h"
 #include "StringReferenceMemberCheck.h"
@@ -46,6 +47,9 @@ public:
         "google-runtime-member-string-references",
         new ClangTidyCheckFactory<runtime::StringReferenceMemberCheck>());
     CheckFactories.addCheckFactory(
+        "google-runtime-memset",
+        new ClangTidyCheckFactory<runtime::MemsetZeroLengthCheck>());
+    CheckFactories.addCheckFactory(
         "google-readability-casting",
         new ClangTidyCheckFactory<readability::AvoidCStyleCastsCheck>());
     CheckFactories.addCheckFactory(
diff --git a/clang-tools-extra/clang-tidy/google/MemsetZeroLengthCheck.cpp b/clang-tools-extra/clang-tidy/google/MemsetZeroLengthCheck.cpp
new file mode 100644
index 00000000000..218a2370632
--- /dev/null
+++ b/clang-tools-extra/clang-tidy/google/MemsetZeroLengthCheck.cpp
@@ -0,0 +1,85 @@
+//===--- MemsetZeroLengthCheck.cpp - clang-tidy -------------------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "MemsetZeroLengthCheck.h"
+#include "clang/ASTMatchers/ASTMatchFinder.h"
+#include "clang/ASTMatchers/ASTMatchers.h"
+#include "clang/AST/ASTContext.h"
+#include "clang/Lex/Lexer.h"
+
+using namespace clang::ast_matchers;
+
+namespace clang {
+namespace tidy {
+namespace runtime {
+
+void
+MemsetZeroLengthCheck::registerMatchers(ast_matchers::MatchFinder *Finder) {
+  auto InTemplateInstantiation = hasAncestor(
+      decl(anyOf(recordDecl(ast_matchers::isTemplateInstantiation()),
+                 functionDecl(ast_matchers::isTemplateInstantiation()))));
+  // Look for memset(x, y, 0) as those is most likely an argument swap.
+  // TODO: Also handle other standard functions that suffer from the same
+  //       problem, e.g. memchr.
+  Finder->addMatcher(
+      callExpr(callee(functionDecl(hasName("::memset"))), argumentCountIs(3),
+               unless(InTemplateInstantiation)).bind("decl"),
+      this);
+}
+
+/// \brief Get a StringRef representing a SourceRange.
+static StringRef getAsString(const MatchFinder::MatchResult &Result,
+                             SourceRange R) {
+  const SourceManager &SM = *Result.SourceManager;
+  // Don't even try to resolve macro or include contraptions. Not worth emitting
+  // a fixit for.
+  if (R.getBegin().isMacroID() ||
+      !SM.isWrittenInSameFile(R.getBegin(), R.getEnd()))
+    return StringRef();
+
+  const char *Begin = SM.getCharacterData(R.getBegin());
+  const char *End = SM.getCharacterData(Lexer::getLocForEndOfToken(
+      R.getEnd(), 0, SM, Result.Context->getLangOpts()));
+
+  return StringRef(Begin, End - Begin);
+}
+
+void MemsetZeroLengthCheck::check(const MatchFinder::MatchResult &Result) {
+  const auto *Call = Result.Nodes.getNodeAs<CallExpr>("decl");
+
+  const Expr *Arg1 = Call->getArg(1);
+  const Expr *Arg2 = Call->getArg(2);
+
+  // Try to evaluate the second argument so we can also find values that are not
+  // just literals. We don't emit a warning if the second argument also
+  // evaluates to zero.
+  llvm::APSInt Value1, Value2;
+  if (!Arg2->EvaluateAsInt(Value2, *Result.Context) || Value2 != 0 ||
+      (Arg1->EvaluateAsInt(Value1, *Result.Context) && Value1 == 0))
+    return;
+
+  // Emit a warning and fix-its to swap the arguments.
+  auto D = diag(Call->getLocStart(),
+                "memset of size zero, potentially swapped arguments");
+  SourceRange LHSRange = Arg1->getSourceRange();
+  SourceRange RHSRange = Arg2->getSourceRange();
+  StringRef RHSString = getAsString(Result, RHSRange);
+  StringRef LHSString = getAsString(Result, LHSRange);
+  if (LHSString.empty() || RHSString.empty())
+    return;
+
+  D << FixItHint::CreateReplacement(CharSourceRange::getTokenRange(LHSRange),
+                                    RHSString)
+    << FixItHint::CreateReplacement(CharSourceRange::getTokenRange(RHSRange),
+                                    LHSString);
+}
+
+} // namespace runtime
+} // namespace tidy
+} // namespace clang
diff --git a/clang-tools-extra/clang-tidy/google/MemsetZeroLengthCheck.h b/clang-tools-extra/clang-tidy/google/MemsetZeroLengthCheck.h
new file mode 100644
index 00000000000..0fd539393a8
--- /dev/null
+++ b/clang-tools-extra/clang-tidy/google/MemsetZeroLengthCheck.h
@@ -0,0 +1,35 @@
+//===--- MemsetZeroLengthCheck.h - clang-tidy ---------------------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_GOOGLE_MEMSET_ZERO_LENGTH_CHECK_H
+#define LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_GOOGLE_MEMSET_ZERO_LENGTH_CHECK_H
+
+#include "../ClangTidy.h"
+
+namespace clang {
+namespace tidy {
+namespace runtime {
+
+/// \brief Finds calls to memset with a literal zero in the length argument.
+///
+/// This is most likely unintended and the length and value arguments are
+/// swapped.
+///
+/// Corresponding cpplint.py check name: 'runtime/memset'.
+class MemsetZeroLengthCheck : public ClangTidyCheck {
+public:
+  void registerMatchers(ast_matchers::MatchFinder *Finder) override;
+  void check(const ast_matchers::MatchFinder::MatchResult &Result) override;
+};
+
+} // namespace runtime
+} // namespace tidy
+} // namespace clang
+
+#endif // LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_GOOGLE_MEMSET_ZERO_LENGTH_CHECK_H
diff --git a/clang-tools-extra/test/clang-tidy/google-memset-zero-length.cpp b/clang-tools-extra/test/clang-tidy/google-memset-zero-length.cpp
new file mode 100644
index 00000000000..262eb51d625
--- /dev/null
+++ b/clang-tools-extra/test/clang-tidy/google-memset-zero-length.cpp
@@ -0,0 +1,51 @@
+// RUN: $(dirname %s)/check_clang_tidy_fix.sh %s google-runtime-memset %t
+// REQUIRES: shell
+
+void *memset(void *, int, __SIZE_TYPE__);
+
+namespace std {
+  using ::memset;
+}
+
+template <int i>
+void memtmpl() {
+  memset(0, sizeof(int), i);
+  memset(0, sizeof(int), 0);
+// CHECK-MESSAGES: :[[@LINE-1]]:3: warning: memset of size zero, potentially swapped argument
+// CHECK-FIXES: memset(0, 0, sizeof(int));
+}
+
+void foo(void *a, int xsize, int ysize) {
+  memset(a, sizeof(int), 0);
+// CHECK-MESSAGES: :[[@LINE-1]]:3: warning: memset of size zero, potentially swapped argument
+// CHECK-FIXES: memset(a, 0, sizeof(int));
+#define M memset(a, sizeof(int), 0);
+  M
+// CHECK-MESSAGES: :[[@LINE-1]]:3: warning: memset of size zero, potentially swapped argument
+// CHECK-FIXES: #define M memset(a, sizeof(int), 0);
+  ::memset(a, xsize *
+           ysize, 0);
+// CHECK-MESSAGES: :[[@LINE-2]]:3: warning: memset of size zero, potentially swapped argument
+// CHECK-FIXES: ::memset(a, 0, xsize *
+// CHECK-FIXES-NEXT: ysize);
+  std::memset(a, sizeof(int), 0x00);
+// CHECK-MESSAGES: :[[@LINE-1]]:3: warning: memset of size zero, potentially swapped argument
+// CHECK-FIXES: std::memset(a, 0x00, sizeof(int));
+
+  const int v = 0;
+  memset(a, sizeof(int), v);
+// CHECK-MESSAGES: :[[@LINE-1]]:3: warning: memset of size zero, potentially swapped argument
+// CHECK-FIXES: memset(a, v, sizeof(int));
+
+  memset(a, sizeof(int), v + v);
+// CHECK-MESSAGES: :[[@LINE-1]]:3: warning: memset of size zero, potentially swapped argument
+// CHECK-FIXES: memset(a, v + v, sizeof(int));
+
+  memset(a, sizeof(int), v + 1);
+
+  memset(a, -1, sizeof(int));
+  memset(a, 0xcd, 1);
+  memset(a, v, 0);
+
+  memtmpl<0>();
+}