[SYCL][ESIMD] Fix compile-time evaluated functions, add test.

Signed-off-by: Konstantin S Bobrovsky <konstantin.s.bobrovsky@intel.com>

Author: kbobrovs

sycl/include/CL/sycl/intel/esimd/detail/esimd_util.hpp

@@ -31,11 +31,11 @@ template <unsigned int N, unsigned int K> struct NextPowerOf2<N, K, false> {
   }
 };
 
-template <unsigned int N> unsigned int getNextPowerOf2() {
+template <unsigned int N> constexpr unsigned int getNextPowerOf2() {
   return NextPowerOf2<N, 1, (1 >= N)>::get();
 }
 
-template <> unsigned int getNextPowerOf2<0>() { return 0; }
+template <> constexpr unsigned int getNextPowerOf2<0>() { return 0; }
 
 /// Compute binary logarithm of a constexpr with guaranteed compile-time
 /// evaluation.

sycl/test/regression/esimd-util-compiler-eval.cpp

@@ -0,0 +1,15 @@
+// RUN: %clangxx -fsycl -fsycl-explicit-simd -fsycl-device-only -c %s
+// This test checks compile-time evaluation of functions from esimd_util.hpp
+
+#include "CL/sycl.hpp"
+#include "CL/sycl/intel/esimd/esimd.hpp"
+
+static_assert(__esimd::getNextPowerOf2<0>() == 0, "");
+static_assert(__esimd::getNextPowerOf2<1>() == 1, "");
+static_assert(__esimd::getNextPowerOf2<7>() == 8, "");
+static_assert(__esimd::getNextPowerOf2<1024>() == 1024, "");
+
+static_assert(__esimd::log2<0>() == 0, "");
+static_assert(__esimd::log2<1>() == 0, "");
+static_assert(__esimd::log2<7>() == 2, "");
+static_assert(__esimd::log2<1024 * 1024>() == 20, "");