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emit_x64_vector: GNFI+SSSE3 implementation of EmitVectorReverseBits

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Performs a full 128-bit bit-reversal using only two instructions.

First by reversing all the bits of each byte using a galois matrix
multiplication(vgf2p8affineqb, Icelake), and then by reversing the bytes
themselves(pshufb, ssse3).
This commit is contained in:
Wunkolo 2020-09-09 10:06:33 -07:00 committed by merry
parent eb00bea1ff
commit 6bb49726f4
1 changed files with 37 additions and 29 deletions
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10
src/backend/x64/emit_x64_vector.cpp
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@ -2747,8 +2747,15 @@ void EmitX64::EmitVectorReverseBits(EmitContext& ctx, IR::Inst* inst) {
auto args = ctx.reg_alloc.GetArgumentInfo(inst);
const Xbyak::Xmm data = ctx.reg_alloc.UseScratchXmm(args[0]);
const Xbyak::Xmm high_nibble_reg = ctx.reg_alloc.ScratchXmm();
if (code.HasAVX512_Icelake() && code.HasSSSE3()) {
// GFNI(vgf2p8affineqb) and SSSE3(pshuf)
// Reverse bits within bytes
code.vgf2p8affineqb(data, data, code.MConst(xword_b, 0x8040201008040201), 0);
// Reverse bytes within vector
code.pshufb(data, code.MConst(xword, 0x0001020304050607, 0x08090a0b0c0d0e0f));
} else {
const Xbyak::Xmm high_nibble_reg = ctx.reg_alloc.ScratchXmm();
code.movdqa(high_nibble_reg, code.MConst(xword, 0xF0F0F0F0F0F0F0F0, 0xF0F0F0F0F0F0F0F0));
code.pand(high_nibble_reg, data);
code.pxor(data, high_nibble_reg);
@ -2782,6 +2789,7 @@ void EmitX64::EmitVectorReverseBits(EmitContext& ctx, IR::Inst* inst) {
code.paddd(data, data);
code.por(data, high_nibble_reg);
}
}
ctx.reg_alloc.DefineValue(inst, data);
}