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emit_x64_vector: GNFI implementation of EmitVectorLogicalShiftRight8

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Bitshifts of the GFNI identity matrix generates a new matrix that
applies lane-wise bitshifts as well. This allows for a fast
single-instruction implementation of a byte-lane bitshift.
This commit is contained in:
Wunkolo 2020-10-28 06:32:11 -07:00 committed by merry
parent 46f96904db
commit 5cc646ffed
1 changed files with 10 additions and 4 deletions
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14
src/backend/x64/emit_x64_vector.cpp
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@ -1510,11 +1510,17 @@ void EmitX64::EmitVectorLogicalShiftRight8(EmitContext& ctx, IR::Inst* inst) {
const u8 shift_amount = args[1].GetImmediateU8();
if (shift_amount > 0) {
const u64 replicand = 0xFEULL >> shift_amount;
const u64 mask = Common::Replicate(replicand, Common::BitSize<u8>());
if (code.HasAVX512_Icelake()) {
// Galois 8x8 identity matrix, bit-shifted by the shift-amount
const u64 shift_matrix = 0x0102040810204080 << (shift_amount * 8);
code.vgf2p8affineqb(result, result, code.MConst(xword_b, shift_matrix), 0);
} else {
const u64 replicand = 0xFEULL >> shift_amount;
const u64 mask = Common::Replicate(replicand, Common::BitSize<u8>());
code.psrlw(result, shift_amount);
code.pand(result, code.MConst(xword, mask, mask));
code.psrlw(result, shift_amount);
code.pand(result, code.MConst(xword, mask, mask));
}
}
ctx.reg_alloc.DefineValue(inst, result);