Merge pull request #8779 from vpisarev:empty_cmp_fix

modules/core/src/arithm.cpp

@@ -1276,7 +1276,7 @@ void cv::compare(InputArray _src1, InputArray _src2, OutputArray _dst, int op)
     src1 = src1.reshape(1); src2 = src2.reshape(1);
     Mat dst = _dst.getMat().reshape(1);
 
-    size_t esz = src1.elemSize();
+    size_t esz = std::max(src1.elemSize(), (size_t)1);
     size_t blocksize0 = (size_t)(BLOCK_SIZE + esz-1)/esz;
     BinaryFuncC func = getCmpFunc(depth1);
 

modules/core/test/test_arithm.cpp

@@ -1912,3 +1912,13 @@ TEST(Subtract, scalarc4_matc4)
 
     ASSERT_EQ(0, cv::norm(cv::Mat(5, 5, CV_8UC4, cv::Scalar::all(250)), destImage, cv::NORM_INF));
 }
+
+TEST(Compare, empty)
+{
+    cv::Mat temp, dst1, dst2;
+    cv::compare(temp, temp, dst1, cv::CMP_EQ);
+    dst2 = temp > 5;
+
+    EXPECT_TRUE(dst1.empty());
+    EXPECT_TRUE(dst2.empty());
+}