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[SYCL][ESIMD] Implement compile-time getNextPowerOf2 w/o recursion. #2133

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Merged
merged 1 commit into from
Jul 22, 2020
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[SYCL][ESIMD] Implement compile-time getNextPowerOf2 w/o recursion. #2133

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44 changes: 36 additions & 8 deletions sycl/include/CL/sycl/intel/esimd/detail/esimd_util.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -17,10 +17,42 @@ namespace __esimd {
/// Constant in number of bytes.
enum { BYTE = 1, WORD = 2, DWORD = 4, QWORD = 8, OWORD = 16, GRF = 32 };

/// Compute the next power of 2 at compile time.
static ESIMD_INLINE constexpr unsigned int getNextPowerOf2(unsigned int n,
unsigned int k = 1) {
return (k >= n) ? k : getNextPowerOf2(n, k * 2);
/// Compute next power of 2 of a constexpr with guaranteed compile-time
/// evaluation.
template <unsigned int N, unsigned int K, bool K_gt_eq_N> struct NextPowerOf2;

template <unsigned int N, unsigned int K> struct NextPowerOf2<N, K, true> {
static constexpr unsigned int get() { return K; }
};

template <unsigned int N, unsigned int K> struct NextPowerOf2<N, K, false> {
static constexpr unsigned int get() {
return NextPowerOf2<N, K * 2, K * 2 >= N>::get();
}
};

template <unsigned int N> unsigned int getNextPowerOf2() {
return NextPowerOf2<N, 1, (1 >= N)>::get();
}

template <> unsigned int getNextPowerOf2<0>() { return 0; }

/// Compute binary logarithm of a constexpr with guaranteed compile-time
/// evaluation.
template <unsigned int N, bool N_gt_1> struct Log2;

template <unsigned int N> struct Log2<N, false> {
static constexpr unsigned int get() { return 0; }
};

template <unsigned int N> struct Log2<N, true> {
static constexpr unsigned int get() {
return 1 + Log2<(N >> 1), ((N >> 1) > 1)>::get();
}
};

template <unsigned int N> constexpr unsigned int log2() {
return Log2<N, (N > 1)>::get();
}

/// Check if a given 32 bit positive integer is a power of 2 at compile time.
Expand All @@ -33,10 +65,6 @@ static ESIMD_INLINE constexpr bool isPowerOf2(unsigned int n,
return (n & (n - 1)) == 0 && n <= limit;
}

static ESIMD_INLINE constexpr unsigned log2(unsigned n) {
return (n > 1) ? 1 + log2(n >> 1) : 0;
}

} // namespace __esimd

__SYCL_INLINE_NAMESPACE(cl) {
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2 changes: 1 addition & 1 deletion sycl/include/CL/sycl/intel/esimd/esimd_math.hpp
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Expand Up @@ -1884,7 +1884,7 @@ T1 esimd_reduce(simd<T1, SZ> v) {
if constexpr (isPowerOf2) {
return esimd_reduce_single<T0, T1, SZ, OpType>(v);
} else {
constexpr unsigned N1 = 1u << __esimd::log2(SZ);
constexpr unsigned N1 = 1u << __esimd::log2<SZ>();
constexpr unsigned N2 = SZ - N1;

simd<T1, N1> v1 = v.template select<N1, 1>(0);
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4 changes: 2 additions & 2 deletions sycl/include/CL/sycl/intel/esimd/esimd_memory.hpp
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Expand Up @@ -567,7 +567,7 @@ media_block_load(AccessorTy acc, unsigned x, unsigned y) {
static_assert(plane <= 3u, "valid plane index is in range [0, 3]");
#if defined(__SYCL_DEVICE_ONLY__) && defined(__SYCL_EXPLICIT_SIMD__)
constexpr unsigned int RoundedWidth =
Width < 4 ? 4 : __esimd::getNextPowerOf2(Width);
Width < 4 ? 4 : __esimd::getNextPowerOf2<Width>();

if constexpr (Width < RoundedWidth) {
constexpr unsigned int n1 = RoundedWidth / sizeof(T);
Expand Down Expand Up @@ -617,7 +617,7 @@ media_block_store(AccessorTy acc, unsigned x, unsigned y, simd<T, m * n> vals) {
static_assert(plane <= 3u, "valid plane index is in range [0, 3]");
#if defined(__SYCL_DEVICE_ONLY__) && defined(__SYCL_EXPLICIT_SIMD__)
constexpr unsigned int RoundedWidth =
Width < 4 ? 4 : __esimd::getNextPowerOf2(Width);
Width < 4 ? 4 : __esimd::getNextPowerOf2<Width>();
constexpr unsigned int n1 = RoundedWidth / sizeof(T);

if constexpr (Width < RoundedWidth) {
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