tests/checkasm: add overflow test for hevc_add_res

Add overflow test for hevc_add_res when int16_t coeff = -32768.

The result of C is good, while ASM is not.

To verify:
    make fate-checkasm-hevc_add_res
    ffmpeg/tests/checkasm/checkasm --test=hevc_add_res

./checkasm --test=hevc_add_res
checkasm: using random seed 679391863
MMXEXT:
    hevc_add_res_4x4_8_mmxext (hevc_add_res.c:69)
  - hevc_add_res.add_residual [FAILED]
SSE2:
    hevc_add_res_8x8_8_sse2 (hevc_add_res.c:69)
    hevc_add_res_16x16_8_sse2 (hevc_add_res.c:69)
    hevc_add_res_32x32_8_sse2 (hevc_add_res.c:69)
  - hevc_add_res.add_residual [FAILED]
AVX:
    hevc_add_res_8x8_8_avx (hevc_add_res.c:69)
    hevc_add_res_16x16_8_avx (hevc_add_res.c:69)
    hevc_add_res_32x32_8_avx (hevc_add_res.c:69)
  - hevc_add_res.add_residual [FAILED]
AVX2:
    hevc_add_res_32x32_8_avx2 (hevc_add_res.c:69)
  - hevc_add_res.add_residual [FAILED]
checkasm: 8 of 14 tests have failed

Signed-off-by: Xu Guangxin <guangxin.xu@intel.com>
Signed-off-by: Linjie Fu <linjie.fu@intel.com>
Signed-off-by: Anton Khirnov <anton@khirnov.net>

tests/checkasm/hevc_add_res.c

@@ -42,7 +42,7 @@
             AV_WN16A(buf + j * 2, rnd() & 0x3FF); \
     } while (0)
 
-static void compare_add_res(int size, ptrdiff_t stride)
+static void compare_add_res(int size, ptrdiff_t stride, int overflow_test)
 {
     LOCAL_ALIGNED_32(int16_t, res0, [32 * 32]);
     LOCAL_ALIGNED_32(int16_t, res1, [32 * 32]);
@@ -53,6 +53,8 @@ static void compare_add_res(int size, ptrdiff_t stride)
 
     randomize_buffers(res0, size);
     randomize_buffers2(dst0, size);
+    if (overflow_test)
+        res0[0] = 0x8000;
     memcpy(res1, res0, sizeof(*res0) * size);
     memcpy(dst1, dst0, sizeof(int16_t) * size);
 
@@ -73,7 +75,9 @@ static void check_add_res(HEVCDSPContext h, int bit_depth)
         ptrdiff_t stride = block_size << (bit_depth > 8);
 
         if (check_func(h.add_residual[i - 2], "hevc_add_res_%dx%d_%d", block_size, block_size, bit_depth)) {
-            compare_add_res(size, stride);
+            compare_add_res(size, stride, 0);
+            // overflow test for res = -32768
+            compare_add_res(size, stride, 1);
         }
     }
 }