Merge pull request #776 from 9prady9/gcc8_fix

Fix compilation errors with GCC 8

Author: jszuppe

include/boost/compute/memory/svm_ptr.hpp

@@ -126,7 +126,7 @@ class svm_ptr
         return m_ptr - other.m_ptr;
     }
 
-    context& get_context() const
+    const context& get_context() const
     {
         return m_context;
     }

test/test_device.cpp

@@ -236,9 +236,10 @@ BOOST_AUTO_TEST_CASE(get_info_specializations)
 #ifdef BOOST_COMPUTE_CL_VERSION_2_1
 BOOST_AUTO_TEST_CASE(get_host_timer)
 {
+    boost::compute::device device = boost::compute::system::default_device();
+
     REQUIRES_OPENCL_VERSION(2, 1);
 
-    boost::compute::device device = boost::compute::system::default_device();
     BOOST_CHECK(device.get_host_timer() != 0);
 
     #ifndef BOOST_COMPUTE_NO_HDR_CHRONO
@@ -254,9 +255,10 @@ BOOST_AUTO_TEST_CASE(get_host_timer)
 
 BOOST_AUTO_TEST_CASE(get_device_and_host_timer)
 {
+    boost::compute::device device = boost::compute::system::default_device();
+
     REQUIRES_OPENCL_VERSION(2, 1);
 
-    boost::compute::device device = boost::compute::system::default_device();
     typedef std::pair<boost::compute::ulong_, boost::compute::ulong_> dah_timer;
     dah_timer timer;
     BOOST_CHECK_NO_THROW(timer = device.get_device_and_host_timer());
@@ -278,10 +280,10 @@ BOOST_AUTO_TEST_CASE(get_device_and_host_timer)
 
 BOOST_AUTO_TEST_CASE(get_info_opencl21_queries)
 {
-    REQUIRES_OPENCL_VERSION(2, 1);
-
     boost::compute::device device = boost::compute::system::default_device();
 
+    REQUIRES_OPENCL_VERSION(2, 1);
+
     BOOST_CHECK(!device.get_info<CL_DEVICE_IL_VERSION>().empty());
     BOOST_CHECK(device.get_info<CL_DEVICE_MAX_NUM_SUB_GROUPS>() > 0);
     BOOST_CHECK_NO_THROW(