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Add a generic Eigen backend based on clang vector extensions

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The goal of this MR is to implement a generic SIMD backend (packet ops) for Eigen that uses clang vector extensions instead of platform-dependent intrinsics. Ideally, this should make it possible to build Eigen and achieve reasonable speed on any platform that has a recent clang compiler, without having to write any inline assembly or intrinsics.

Caveats:

* The current implementation is a proof of concept and supports vectorization for float, double, int32_t, and int64_t using fixed-size 512-bit vectors (a somewhat arbitrary choice). I have not done much to tune this for speed yet.
* For now, there is no way to enable this other than setting -DEIGEN_VECTORIZE_GENERIC on the command line.
* This only compiles with newer versions of clang. I have tested that it compiles and all tests pass with clang 19.1.7.

https://clang.llvm.org/docs/LanguageExtensions.html#vectors-and-extended-vectors

Closes #2998 and #2997

See merge request libeigen/eigen!2051

Co-authored-by: Rasmus Munk Larsen <rmlarsen@google.com>
Co-authored-by: Antonio Sánchez <cantonios@google.com>
This commit is contained in:
Rasmus Munk Larsen
2025-11-06 21:52:19 +00:00
parent 7c7d84735e
commit ec93a6d098
17 changed files with 1161 additions and 39 deletions
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4
test/packetmath.cpp
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@@ -685,8 +685,8 @@ void packetmath() {
int HalfPacketSize = PacketSize > 4 ? PacketSize / 2 : PacketSize;
for (int i = 0; i < HalfPacketSize; ++i) ref[i] = Scalar(0);
for (int i = 0; i < PacketSize; ++i) ref[i % HalfPacketSize] += data1[i];
internal::pstore(data2, internal::predux_half_dowto4(internal::pload<Packet>(data1)));
VERIFY(test::areApprox(ref, data2, HalfPacketSize) && "internal::predux_half_dowto4");
internal::pstore(data2, internal::predux_half(internal::pload<Packet>(data1)));
VERIFY(test::areApprox(ref, data2, HalfPacketSize) && "internal::predux_half");
}
// Avoid overflows.