[ESIMD] Optimize the simd stride constructor #12553
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✅ With the latest revision this PR passed the C/C++ code formatter. |
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simd(base, stride) calls previously were lowered into a long sequence of
INSERT and ADD operations. That sequence is replaced with a vector
equivalent:
vbase = broadcast base
vstride = broadcast stride
vstride_coef = {0, 1, 2, 3, ... N-1}
vec_result = vbase + vstride * vstride_coef;
Signed-off-by: Klochkov, Vyacheslav N <[email protected]>
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sarnex
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Feb 5, 2024
| std::index_sequence<Is...>) { | ||
| return vector_type_t<T, N>{(T)(Base + ((T)Is) * Stride)...}; | ||
| constexpr auto make_vector_impl(T Base, T Stride, std::index_sequence<Is...>) { | ||
| using CppT = typename element_type_traits<T>::EnclosingCppT; |
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I remember you considering optimizing this for low values of N, did that end up not being worth it?
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I did the initial research for float types and found such tuning worthless.
Just to answer your question here and to show the IR I used int type this time,
and found 2 cases where the old code is 1 instruction faster/shorter:
old {num math ops : ops} new {num math ops : ops}
simd<int, 1> 0: 0:
simd<int, 2> * 1: 1xADD 2: 1xADD, 1xMUL
simd<int, 3> * 3: 2xADD, 1xSHL 4: 2xADD, 2xMUL (it split 3-elem vec to 2-elem vec + 1-elem vec)
simd<int, 4> 5: 3xADD, 1xSHL, 1xMUL 2: 1xADD, 1xMUL
simd<float, 1> 0: 0:
simd<float, 2> 1: 1xADD 1: 1xMAD
simd<float, 3> 2: 2xADD 2: 2xMAD (3-elem vector ops were split -> 2-elem + 1-elem)
simd<float, 4> 3: 3xADD 1: 1xMAD
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I added few lines of code to tune for integral types and N <= 3: ea002b5
The old sequence prodices 1 less instruction in the final gpu code. Signed-off-by: Klochkov, Vyacheslav N <[email protected]>
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simd(base, stride) calls previously were lowered into a long sequence of INSERT and ADD operations. That sequence is replaced with a vector equivalent:
vbase = broadcast base
vstride = broadcast stride
vstride_coef = {0, 1, 2, 3, ... N-1}
vec_result = vbase + vstride * vstride_coef;