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EmitPackedHalvingSub{U,S}16: SSE2 implementation

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This commit is contained in:
MerryMage 2017-12-14 15:04:20 +00:00
parent a98821da41
commit dc357c780d
1 changed files with 15 additions and 34 deletions
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49
src/backend_x64/emit_x64.cpp
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@ -1993,28 +1993,22 @@ void EmitX64::EmitPackedHalvingSubS8(RegAlloc& reg_alloc, IR::Block&, IR::Inst*
void EmitX64::EmitPackedHalvingSubU16(RegAlloc& reg_alloc, IR::Block&, IR::Inst* inst) {
auto args = reg_alloc.GetArgumentInfo(inst);
Xbyak::Reg32 minuend = reg_alloc.UseScratchGpr(args[0]).cvt32();
Xbyak::Reg32 subtrahend = reg_alloc.UseScratchGpr(args[1]).cvt32();
Xbyak::Xmm minuend = reg_alloc.UseScratchXmm(args[0]);
Xbyak::Xmm subtrahend = reg_alloc.UseScratchXmm(args[1]);
// This relies on the equality x-y == (x^y) - (((x^y)&y) << 1).
// Note that x^y always contains the LSB of the result.
// Since we want to calculate (x+y)/2, we can instead calculate ((x^y)>>1) - ((x^y)&y).
// Since we want to calculate (x-y)/2, we can instead calculate ((x^y)>>1) - ((x^y)&y).
code->xor_(minuend, subtrahend);
code->and_(subtrahend, minuend);
code->shr(minuend, 1);
code->pxor(minuend, subtrahend);
code->pand(subtrahend, minuend);
code->psrlw(minuend, 1);
// At this point,
// minuend := (a^b) >> 1
// subtrahend := (a^b) & b
// We must now perform a partitioned subtraction.
// We can do this because minuend contains 15 bit fields.
// We use the extra bit in minuend as a bit to borrow from; we set this bit.
// We invert this bit at the end as this tells us if that bit was borrowed from.
code->or_(minuend, 0x80008000);
code->sub(minuend, subtrahend);
code->xor_(minuend, 0x80008000);
code->psubw(minuend, subtrahend);
reg_alloc.DefineValue(inst, minuend);
}
@ -2022,35 +2016,22 @@ void EmitX64::EmitPackedHalvingSubU16(RegAlloc& reg_alloc, IR::Block&, IR::Inst*
void EmitX64::EmitPackedHalvingSubS16(RegAlloc& reg_alloc, IR::Block&, IR::Inst* inst) {
auto args = reg_alloc.GetArgumentInfo(inst);
Xbyak::Reg32 minuend = reg_alloc.UseScratchGpr(args[0]).cvt32();
Xbyak::Reg32 subtrahend = reg_alloc.UseScratchGpr(args[1]).cvt32();
Xbyak::Reg32 carry = reg_alloc.ScratchGpr().cvt32();
Xbyak::Xmm minuend = reg_alloc.UseScratchXmm(args[0]);
Xbyak::Xmm subtrahend = reg_alloc.UseScratchXmm(args[1]);
// This relies on the equality x-y == (x^y) - (((x^y)&y) << 1).
// Note that x^y always contains the LSB of the result.
// Since we want to calculate (x-y)/2, we can instead calculate ((x^y)>>1) - ((x^y)&y).
// Since we want to calculate (x-y)/2, we can instead calculate ((x^y)>>>1) - ((x^y)&y).
code->xor_(minuend, subtrahend);
code->and_(subtrahend, minuend);
code->mov(carry, minuend);
code->and_(carry, 0x80008000);
code->shr(minuend, 1);
code->pxor(minuend, subtrahend);
code->pand(subtrahend, minuend);
code->psraw(minuend, 1);
// At this point,
// minuend := (a^b) >> 1
// minuend := (a^b) >>> 1
// subtrahend := (a^b) & b
// carry := (a^b) & 0x80008000
// We must now perform a partitioned subtraction.
// We can do this because minuend contains 7 bit fields.
// We use the extra bit in minuend as a bit to borrow from; we set this bit.
// We invert this bit at the end as this tells us if that bit was borrowed from.
// We then sign extend the result into this bit.
code->or_(minuend, 0x80008000);
code->sub(minuend, subtrahend);
code->xor_(minuend, 0x80008000);
code->xor_(minuend, carry);
code->psubw(minuend, subtrahend);
reg_alloc.DefineValue(inst, minuend);
}