PPU/SPU LLVM: Emulate VPERM2B with a 256 bit wide VPERMB (AVX512 optimization) #10959
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- Save 1 uop by using 256 wide VPERMB instead of VPERM2B. (Compiles down to a vinserti128 and vpermb)
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Saves 1 uop by using 256 wide VPERMB instead of VPERM2B. (Compiles down to a vinserti128 and vpermb)
On my tigerlake laptop the AVX2 path has a throughput of one shufb per 4 cycles. The old AVX512 path has a throughput of 1 per 3 cycles, and the new AVX512 path has a throughput of 1 per 2.3 cycles. (tested in a little benchmark I wrote in asm before I rewrote it in LLVM IR.)