[clang-tidy] Also emit a warning for memset(x, 0, 0)

It doesn't make sense to suggest swapping the arguments here but it's
still useless code

llvm-svn: 213156

clang-tools-extra/clang-tidy/google/MemsetZeroLengthCheck.cpp

@@ -57,13 +57,17 @@ void MemsetZeroLengthCheck::check(const MatchFinder::MatchResult &Result) {
   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.
+  // just literals.
   llvm::APSInt Value1, Value2;
-  if (!Arg2->EvaluateAsInt(Value2, *Result.Context) || Value2 != 0 ||
-      (Arg1->EvaluateAsInt(Value1, *Result.Context) && Value1 == 0))
+  if (!Arg2->EvaluateAsInt(Value2, *Result.Context) || Value2 != 0)
     return;
 
+  // If both arguments evaluate to zero emit a warning without fix suggestions.
+  if (Arg1->EvaluateAsInt(Value1, *Result.Context) && Value1 == 0) {
+    diag(Call->getLocStart(), "memset of size zero");
+    return;
+  }
+
   // Emit a warning and fix-its to swap the arguments.
   auto D = diag(Call->getLocStart(),
                 "memset of size zero, potentially swapped arguments");

clang-tools-extra/test/clang-tidy/google-memset-zero-length.cpp

@@ -46,6 +46,8 @@ void foo(void *a, int xsize, int ysize) {
   memset(a, -1, sizeof(int));
   memset(a, 0xcd, 1);
   memset(a, v, 0);
+// CHECK-MESSAGES: :[[@LINE-1]]:3: warning: memset of size zero
+// CHECK-FIXES: memset(a, v, 0);
 
   memtmpl<0>();
 }