core(ocl): add flag OPENCV_OPENCL_ENABLE_MEM_USE_HOST_PTR

to control CL_MEM_USE_HOST_PTR usage

modules/core/src/ocl.cpp

@@ -267,6 +267,9 @@ static const String getBuildExtraOptions()
     return param_buildExtraOptions;
 }
 
+static const bool CV_OPENCL_ENABLE_MEM_USE_HOST_PTR = utils::getConfigurationParameterBool("OPENCV_OPENCL_ENABLE_MEM_USE_HOST_PTR", true);
+static const size_t CV_OPENCL_ALIGNMENT_MEM_USE_HOST_PTR = utils::getConfigurationParameterSizeT("OPENCV_OPENCL_ALIGNMENT_MEM_USE_HOST_PTR", 4);
+
 #endif // HAVE_OPENCL
 
 struct UMat2D
@@ -4675,6 +4678,9 @@ public:
 
     bool allocate(UMatData* u, int accessFlags, UMatUsageFlags usageFlags) const CV_OVERRIDE
     {
+#ifndef HAVE_OPENCL
+        return false;
+#else
         if(!u)
             return false;
 
@@ -4749,8 +4755,12 @@ public:
 #endif
             {
                 tempUMatFlags = UMatData::TEMP_UMAT;
-                if (u->origdata == cv::alignPtr(u->origdata, 4)  // There are OpenCL runtime issues for less aligned data
-                    && !(u->originalUMatData && u->originalUMatData->handle)  // Avoid sharing of host memory between OpenCL buffers
+                if (CV_OPENCL_ENABLE_MEM_USE_HOST_PTR
+                    // There are OpenCL runtime issues for less aligned data
+                    && (CV_OPENCL_ALIGNMENT_MEM_USE_HOST_PTR != 0
+                        && u->origdata == cv::alignPtr(u->origdata, (int)CV_OPENCL_ALIGNMENT_MEM_USE_HOST_PTR))
+                    // Avoid sharing of host memory between OpenCL buffers
+                    && !(u->originalUMatData && u->originalUMatData->handle)
                 )
                 {
                     handle = clCreateBuffer(ctx_handle, CL_MEM_USE_HOST_PTR|createFlags,
@@ -4780,6 +4790,7 @@ public:
             u->markHostCopyObsolete(true);
         opencl_allocator_stats.onAllocate(u->size);
         return true;
+#endif  // HAVE_OPENCL
     }
 
     /*void sync(UMatData* u) const
@@ -4908,7 +4919,7 @@ public:
                                 (CL_MAP_READ | CL_MAP_WRITE),
                                 0, u->size, 0, 0, 0, &retval);
                             CV_OCL_CHECK_RESULT(retval, cv::format("clEnqueueMapBuffer(handle=%p, sz=%lld) => %p", (void*)u->handle, (long long int)u->size, data).c_str());
-                            CV_Assert(u->origdata == data);
+                            CV_Assert(u->origdata == data && "Details: https://github.com/opencv/opencv/issues/6293");
                             if (u->originalUMatData)
                             {
                                 CV_Assert(u->originalUMatData->data == data);