[SLP] Failure to vectorize interleaving of elements from two vector loads

[LebedevRI]

Bugzilla Link	45077
Version	trunk
OS	Linux
CC	@alexey-bataev,@dtemirbulatov,@fhahn,@RKSimon

Extended Description

#include

std::array<uint16_t, 16>
zz(const uint16_tconst row0, const uint16_tconst row1) {
std::array<uint16_t, 16> baseline;

// Preload the entire block from last two rows.
std::array<std::array<uint16_t, 16>, 2> prev;
for (int c = 0; c < 16; ++c)
  prev[1][c] = row0[c];
for (int c = 0; c < 16; ++c)
  prev[0][c] = row1[c];

// The differences are specified as compared to the pixels of the previous
// row for even pixels, or to pixels from two rows above for odd pixels.
for (int c = 0; c < 16; ++c)
  baseline[c] = prev[c & 1][c];

return baseline;

}

Currently results in rather scalar code, however i believe this should vectorize into something like

define <16 x i16> @​zz(<16 x i16>* %line0, <16 x i16>* %line1) {
%l0data = load <16 x i16>, <16 x i16>* %line0
%l1data = load <16 x i16>, <16 x i16>* %line1
%res = shufflevector <16 x i16> %l0data, <16 x i16> %l1data,
<16 x i32> <i32 0, i32 17, i32 2, i32 19, i32 4, i32 21, i32 6, i32 23, i32 8, i32 25, i32 10, i32 27, i32 12, i32 29, i32 14, i32 31>
ret <16 x i16> %res
}

https://godbolt.org/z/Pj7XkH