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qfloat16/F16C: rewrite the F16C conversion with overlapping 

We don't have to be completely sequential. It's perfectly fine to
overlap loads and stores and this leads to simpler code.

Change-Id: I6fcda969a9e9427198bffffd16ce56ebbc948379
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@qt.io>
bb10
Thiago Macieira 2022-01-27 21:08:04 -08:00
parent 073454901d
commit ce41151215
1 changed files with 62 additions and 14 deletions
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76
src/corelib/global/qfloat16.cpp
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@ -202,32 +202,80 @@ static inline bool hasFastF16()
QT_FUNCTION_TARGET(F16C)
static void qFloatToFloat16_fast(quint16 *out, const float *in, qsizetype len) noexcept
{
constexpr qsizetype Step = sizeof(__m256i) / sizeof(float);
constexpr qsizetype HalfStep = sizeof(__m128i) / sizeof(float);
qsizetype i = 0;
int epilog_i;
for (; i < len - 7; i += 8)
_mm_storeu_si128((__m128i *)(out + i), _mm256_cvtps_ph(_mm256_loadu_ps(in + i), 0));
if (i < len - 3) {
_mm_storel_epi64((__m128i *)(out + i), _mm_cvtps_ph(_mm_loadu_ps(in + i), 0));
i += 4;
if (len >= Step) {
auto convertOneChunk = [=](qsizetype offset) QT_FUNCTION_TARGET(F16C) {
__m256 f32 = _mm256_loadu_ps(in + offset);
__m128i f16 = _mm256_cvtps_ph(f32, _MM_FROUND_TO_NEAREST_INT);
_mm_storeu_si128(reinterpret_cast<__m128i *>(out + offset), f16);
};
// main loop: convert Step (8) floats per iteration
for ( ; i + Step < len; i += Step)
convertOneChunk(i);
// epilogue: convert the last chunk, possibly overlapping with the last
// iteration of the loop
return convertOneChunk(len - Step);
}
if (len >= HalfStep) {
auto convertOneChunk = [=](qsizetype offset) QT_FUNCTION_TARGET(F16C) {
__m128 f32 = _mm_loadu_ps(in + offset);
__m128i f16 = _mm_cvtps_ph(f32, _MM_FROUND_TO_NEAREST_INT);
_mm_storel_epi64(reinterpret_cast<__m128i *>(out + offset), f16);
};
// two conversions, possibly overlapping
convertOneChunk(0);
return convertOneChunk(len - HalfStep);
}
// Inlining "qfloat16::qfloat16(float f)":
for (epilog_i = 0; i < len && epilog_i < 3; ++i, ++epilog_i)
for ( ; i < len; ++i)
out[i] = _mm_extract_epi16(_mm_cvtps_ph(_mm_set_ss(in[i]), 0), 0);
}
QT_FUNCTION_TARGET(F16C)
static void qFloatFromFloat16_fast(float *out, const quint16 *in, qsizetype len) noexcept
{
constexpr qsizetype Step = sizeof(__m256i) / sizeof(float);
constexpr qsizetype HalfStep = sizeof(__m128i) / sizeof(float);
qsizetype i = 0;
int epilog_i;
for (; i < len - 7; i += 8)
_mm256_storeu_ps(out + i, _mm256_cvtph_ps(_mm_loadu_si128((const __m128i *)(in + i))));
if (i < len - 3) {
_mm_storeu_ps(out + i, _mm_cvtph_ps(_mm_loadl_epi64((const __m128i *)(in + i))));
i += 4;
if (len >= Step) {
auto convertOneChunk = [=](qsizetype offset) QT_FUNCTION_TARGET(F16C) {
__m128i f16 = _mm_loadu_si128(reinterpret_cast<const __m128i *>(in + offset));
__m256 f32 = _mm256_cvtph_ps(f16);
_mm256_storeu_ps(out + offset, f32);
};
// main loop: convert Step (8) floats per iteration
for ( ; i + Step < len; i += Step)
convertOneChunk(i);
// epilogue: convert the last chunk, possibly overlapping with the last
// iteration of the loop
return convertOneChunk(len - Step);
}
if (len >= HalfStep) {
auto convertOneChunk = [=](qsizetype offset) QT_FUNCTION_TARGET(F16C) {
__m128i f16 = _mm_loadl_epi64(reinterpret_cast<const __m128i *>(in + offset));
__m128 f32 = _mm_cvtph_ps(f16);
_mm_storeu_ps(out + offset, f32);
};
// two conversions, possibly overlapping
convertOneChunk(0);
return convertOneChunk(len - HalfStep);
}
// Inlining "qfloat16::operator float()":
for (epilog_i = 0; i < len && epilog_i < 3; ++i, ++epilog_i)
for ( ; i < len; ++i)
out[i] = _mm_cvtss_f32(_mm_cvtph_ps(_mm_cvtsi32_si128(in[i])));
}