GcnSdwaDpp - CLRX/CLRX-mirror GitHub Wiki

GCN 1.2 VOP_SDWA and VOP_DPP encodings

The GCN 1.2 architecture provides two new VOP encoding enhancements which adds new features. The VOP_SDWA adds possibility to choosing and interesting bytes, words in operands. The VOP_DPP adds new parallel features to manipulating wavefronts (moving data between threads).

VOP_SDWA

The VOP_SDWA encoding is enabled by setting 0xf9 in VSRC0 field in VOP1/VOP2/VOPC encoding. In the assembler's syntax you can force this encoding by using SDWA modifier in instruction. List of fields:

Bits Name Description
0-7 SRC0 First source vector operand
8-10 DST_SEL Destination selection
11-12 DST_UNUSED Format for unused bits
13 CLAMP CLAMP modifier
16-18 SRC0_SEL Source data selection for SRC0
19 SRC0_SEXT Signed extension for SRC0
20 SRC0_NEG Negation modifier for SRC0
21 SRC0_ABS Absolute value for SRC0
24-26 SRC0_SEL Source data selectio for SRC1
27 SRC1_SEXT Signed extension for SRC1
28 SRC1_NEG Negation modifier for SRC1
29 SRC1_ABS Absolute value for SRC1

The DST_SEL modifier determines which part of dword will hold first part (with same length) of destination dword. This make operation (RESULT & PARTMASK) << PARTSHIFT. The SRC0_SEL and SRC1_SEL determines which part of source dword will be placed to first part of this source dword. This make operation (SOURCE>>PARTSHIFT) & PARTMASK. Possible part selection for DST_SEL, SRC0_SEL and SRC1_SEL:

Value Name Assembler names Description
0 SDWA_BYTE_0 BYTE0, BYTE_0, B0 Byte 0 of dword
1 SDWA_BYTE_1 BYTE1, BYTE_1, B1 Byte 1 of dword
2 SDWA_BYTE_2 BYTE2, BYTE_2, B2 Byte 2 of dword
3 SDWA_BYTE_3 BYTE3, BYTE_3, B3 Byte 3 of dword
4 SDWA_WORD_0 WORD0, WORD_0, W0 Word 0 of dword
5 SDWA_WORD_1 WORD1, WORD_1, W1 Word 1 of dword
6 SDWA_DWORD DWORD, DW Whole dword

The DST_UNUSED modifier specify how to fill bits that do not hold by choosen part. Following options:

Value Name Assembler name Descrption
0 SDWA_UNUSED_PAD PAD Fill by zeroes
1 SDWA_UNUSED_SEXT SEXT Fill by last bit of parts (sign), zero pad lower bits
2 SDWA_UNUSED_PRESERVE PRESERVE Preserve unused bits

The modifier SEXT (applied by using sext(operand)) apply sign extension (fill bits after part) to source operand while for source operand was not selected whole dword (SDWA_DWORD not choosen).

Examples:

v_xor_b32 v1,v2,v3 dst_sel:byte_1 src0_sel:byte1 src1_sel:word1
v_xor_b32 v1,v2,v3 dst_sel:b1 src0_sel:b1 src1_sel:w1
v_xor_b32 v1,v2,v3 dst_sel:byte_1 src0_sel:byte1 src1_sel:word1 dst_unused:preserve
v_xor_b32 v1,v2,v3 dst_sel:byte_1 src0_sel:byte1 src1_sel:word1 dst_unused:sext
v_xor_b32 v1,sext(v2),v3 dst_sel:byte_1 src0_sel:byte1 src1_sel:word1

Operation code:

// SRC0_SRC = source SRC0, SRC1_SRC = source SRC1, DST_SRC = VDST source
// SRC0_DST = dest. SRC0, SRC1_DST = dest. SRC1, DST_DST = VDST dest.
// OPERATION(SRC0, SRC1) - instruction operation, VDST - VDST register before instruction
switch(SRC0_SEL)
{
    case SDWA_BYTE_0:
        SRC0_DST = (SRC0_SEXT) ? INT32(INT8(SRC0_SRC & 0xff)) : SRC0_SRC & 0xff
        break;
    case SDWA_BYTE_1:
        SRC0_DST = (SRC0_SEXT) ? INT32(INT8((SRC0_SRC>>8) & 0xff)) :
                    (SRC0_SRC>>8) & 0xff
        break;
    case SDWA_BYTE_2:
        SRC0_DST = (SRC0_SEXT) ? INT32(INT8((SRC0_SRC>>16) & 0xff)) :
                    (SRC0_SRC>>16) & 0xff
        break;
    case SDWA_BYTE_3:
        SRC0_DST = (SRC0_SEXT) ? INT32(INT8(SRC0_SRC>>24)) : SRC0_SRC>>24
        break;
    case SDWA_WORD_0:
        SRC0_DST = (SRC0_SEXT) ? INT32(INT16(SRC0_SRC & 0xffff)) : SRC0_SRC & 0xffff
        break;
    case SDWA_WORD_1:
        SRC0_DST = (SRC0_SEXT) ? INT32(INT16(SRC0_SRC >> 16)) : SRC0_SRC >> 16
        break;
    case SDWA_DWORD:
        SRC0_DST = SRC0_SRC
        break;
}
if (HAVE_SRC1)
{
    switch(SRC1_SEL)
    {
        case SDWA_BYTE_0:
            SRC1_DST = (SRC1_SEXT) ? INT32(INT8(SRC1_SRC & 0xff)) : SRC1_SRC & 0xff
            break;
        case SDWA_BYTE_1:
            SRC1_DST = (SRC1_SEXT) ? INT32(INT8((SRC1_SRC>>8) & 0xff)) :
                        (SRC1_SRC>>8) & 0xff
            break;
        case SDWA_BYTE_2:
            SRC1_DST = (SRC1_SEXT) ? INT32(INT8((SRC1_SRC>>16) & 0xff)) :
                        (SRC1_SRC>>16) & 0xff
            break;
        case SDWA_BYTE_3:
            SRC1_DST = (SRC1_SEXT) ? INT32(INT8(SRC1_SRC>>24)) : SRC1_SRC>>24
            break;
        case SDWA_WORD_0:
            SRC1_DST = (SRC1_SEXT) ? INT32(INT16(SRC1_SRC & 0xffff)) : SRC1_SRC & 0xffff
            break;
        case SDWA_WORD_1:
            SRC1_DST = (SRC1_SEXT) ? INT32(INT16(SRC1_SRC >> 16)) : SRC1_SRC >> 16
            break;
        case SDWA_DWORD:
            SRC1_DST = SRC1_SRC
            break;
    }
}
DST_SRC = OPERATION(SRC0_DST,SRC1_DST)
UNT32 tmp
switch(DST_SEL)
{
    case SDWA_BYTE_0:
        tmp = DST_SRC & 0xff
        if (DST_UNUSED==SDWA_UNUSED_PAD)
            DST_DST = tmp
        else if (DST_UNUSED==SDWA_UNUSED_SEXT)
            DST_DST = INT32(INT8(tmp))
        else if (DST_UNUSED==SDWA_UNUSED_PRESERVE)
            DST_DST = tmp | (VDST & 0xffffff00)
        break;
    case SDWA_BYTE_1:
        tmp = DST_SRC & 0xff
        if (DST_UNUSED==SDWA_UNUSED_PAD)
            DST_DST = tmp << 8
        else if (DST_UNUSED==SDWA_UNUSED_SEXT)
            DST_DST = INT32(INT8(tmp)) << 8
        else if (DST_UNUSED==SDWA_UNUSED_PRESERVE)
            DST_DST = (tmp<<8) | (VDST & 0xffff00ff)
        break;
    case SDWA_BYTE_2:
        tmp = DST_SRC & 0xff
        if (DST_UNUSED==SDWA_UNUSED_PAD)
            DST_DST = tmp << 16
        else if (DST_UNUSED==SDWA_UNUSED_SEXT)
            DST_DST = INT32(INT8(tmp)) << 16
        else if (DST_UNUSED==SDWA_UNUSED_PRESERVE)
            DST_DST = (tmp<<16) | (VDST & 0xff00ffff)
        break;
    case SDWA_BYTE_3:
        tmp = DST_SRC & 0xff
        if (DST_UNUSED==SDWA_UNUSED_PAD)
            DST_DST = tmp << 24
        else if (DST_UNUSED==SDWA_UNUSED_SEXT)
            DST_DST = INT32(INT8(tmp)) << 24
        else if (DST_UNUSED==SDWA_UNUSED_PRESERVE)
            DST_DST = (tmp<<24) | (VDST & 0x00ffffff)
        break;
    case SDWA_WORD_0:
        tmp = DST_SRC & 0xffff
        if (DST_UNUSED==SDWA_UNUSED_PAD)
            DST_DST = tmp
        else if (DST_UNUSED==SDWA_UNUSED_SEXT)
            DST_DST = INT32(INT16(tmp))
        else if (DST_UNUSED==SDWA_UNUSED_PRESERVE)
            DST_DST = tmp | (VDST & 0xffff0000)
        break;
    case SDWA_WORD_1:
        tmp = DST_SRC & 0xffff
        if (DST_UNUSED==SDWA_UNUSED_PAD)
            DST_DST = tmp << 16
        else if (DST_UNUSED==SDWA_UNUSED_SEXT)
            DST_DST = INT32(INT16(tmp)) << 16
        else if (DST_UNUSED==SDWA_UNUSED_PRESERVE)
            DST_DST = (tmp<<16) | (VDST & 0xffff)
        break;
    case SDWA_DWORD:
        DST_DST = DST_SRC
        break;
}

VOP_DPP

The VOP_DPP encoding is enabled by setting 0xfa in SRC0 field in VOP1/VOP2/VOPC encoding. In the assembler's syntax you can force this encoding by using DPP modifier in instruction. List of fields:

Bits Name Description
0-7 SRC0 First source vector operand
8-16 DPP_CTRL Data parallel primitive control
19 BOUND_CTRL Specifies behaviour when shared data is invalid
20 SRC0_NEG Negation modifier for SRC0
21 SRC0_ABS Absolute value for SRC0
22 SRC1_NEG Negation modifier for SRC1
23 SRC1_ABS Absolute value for SRC1
24-27 BANK_MASK Bank enable mask
28-31 ROW_MASK Row enable mask

The operation on wavefronts applied to SRC0 operand in VOP instruction. The wavefront contains 4 rows (1 row - 16 threads), and each row contains 4 banks (1 bank - 4 threads). The DPP_CTRL choose which operation will be applied to SRC0. List of data parallel operations:

Value Name Modifier Description
0x00-0xff DPP_QUAD_PERM{00:ff} quad_perm:[A,B,C,D] Full permute of 4 threads
0x101-0x10f DPP_ROW_SL{1:15} row_shl:N Row shift left by N threads
0x111-0x11f DPP_ROW_SR{1:15} row_shr:N Row shift right by N threads
0x121-0x12f DPP_ROW_RR{1:15} row_ror:N Row rotate right by N threads
0x130 DPP_WF_SL1 wave_shl:1 Wave shift left by 1 thread
0x134 DPP_WF_RL1 wave_rol:1 Wave rotate left by 1 thread
0x138 DPP_WF_SR1 wave_shr:1 Wave shift right by 1 thread
0x13c DPP_WF_RR1 wave_ror:1 Wave rotate right by 1 thread
0x140 DPP_ROW_MIRROR row_mirror Mirror threads within row
0x141 DPP_ROW_HALF_MIRROR row_half_mirror Mirror threads within half row
0x142 DPP_ROW_BCAST15 row_bcast:15 Broadcast 15 thread of each row to next row
0x143 DPP_ROW_BCAST31 row_bcast:31 Broadcast 31 thread to row 2 and row 3

The BOUND_CTRL flag (modifier bound_ctrl or bound_ctrl:0) control how to fill invalid threads (for example that last threads after left shifting). Zero value (no modifier) do not perform operation in thread that source threads are invalid. One value (with modifier) fills invalid threads by 0 value.

The field BANK_MASK (modifier bank_mask:value) choose which banks will be enabled during data parallel operation in each enabled row. The Nth bit represents Nth bank in each row. Threads in disabled banks do not perform operation.

The field ROW_MASK (modifier row_mask:value) choose which rows will be enabled during data parallel operation. The Nth bit represents Nth row. Threads in disabled rows do not perform operation.

Examples:

v_xor_b32 v1,v2,v3 quad_perm:[2,3,0,1]
v_xor_b32 v1,v2,v3 row_shl:5
v_xor_b32 v1,v2,v3 row_shr:7
v_xor_b32 v1,v2,v3 row_ror:8
v_xor_b32 v1,v2,v3 wave_shl:1
v_xor_b32 v1,v2,v3 wave_shl
v_xor_b32 v1,v2,v3 wave_shr:1
v_xor_b32 v1,v2,v3 wave_shr
v_xor_b32 v1,v2,v3 wave_rol:1
v_xor_b32 v1,v2,v3 wave_rol
v_xor_b32 v1,v2,v3 wave_ror:1
v_xor_b32 v1,v2,v3 wave_ror
v_xor_b32 v1,v2,v3 row_mirror
v_xor_b32 v1,v2,v3 row_half_mirror
v_xor_b32 v1,v2,v3 row_bcast:15
v_xor_b32 v1,v2,v3 row_bcast:31
v_xor_b32 v1,v2,v3 row_shr:7 bound_ctrl
v_xor_b32 v1,v2,v3 row_shr:7 bound_ctrl:0
v_xor_b32 v1,v2,v3 row_shl:5 row_mask:0b1100
v_xor_b32 v1,v2,v3 row_shl:5 bank_mask:0b0101

Operation code:

// SRC0_SRC[X] - original VSRC0 value from thread X
// SRC0_DST[X] - destination VSRC0 value from thread X
// OPERATION(SRC0, SRC1) - instruction operation, VDST - VDST register before instruction
BYTE invalid = 0
BYTE srcLane
if (DPP_CTRL>=DPP_QUAD_PERM00 && DPP_CTRL<=DPP_QUAD_PERMFF)
{
    BYTE p0 = DPP_CTRL&3
    BYTE p1 = (DPP_CTRL>>2)&3
    BYTE p2 = (DPP_CTRL>>4)&3
    BYTE p3 = (DPP_CTRL>>6)&3
    BYTE curL4 = LANEID&~3
    if (LANEID&3==0)
        srcLane = curL4 + p0
    else if (LANEID&3==1)
        srcLane = curL4 + p1
    else if (LANEID&3==2)
        srcLane = curL4 + p2
    else if (LANEID&3==3)
        srcLane = curL4 + p3    
}
else if (DPP_CTRL>=DPP_ROW_SL1 && DPP_CTRL<=DPP_ROW_SL15)
{
    BYTE shift = DPP_CTRL&15
    BYTE slid = LANEID&15
    BYTE curR = LANEID&~15
    if (slid+shift<=15)
        srcLane = curR + slid + shift
    else
        srcLane = LANESNUM
}
else if (DPP_CTRL>=DPP_ROW_SR1 && DPP_CTRL<=DPP_ROW_SR15)
{
    BYTE shift = DPP_CTRL&15
    BYTE slid = LANEID&15
    BYTE curR = LANEID&~15
    if (slid>=shift)
        srcLane = curR + slid - shift
    else
        srcLane = LANESNUM
}
else if (DPP_CTRL>=DPP_ROW_RR1 && DPP_CTRL<=DPP_ROW_RR15)
{
    BYTE shift = DPP_CTRL&15
    BYTE slid = LANEID&15
    BYTE curR = LANEID&~15
    srcLane = curR + ((16+slid - shift)&15)
}
else if (DPP_CTRL==DPP_WF_SL1)
    srcLane = LANEID+1
else if (DPP_CTRL==DPP_WF_SR1)
    srcLane = LANEID-1
else if (DPP_CTRL==DPP_WF_RL1)
    srcLane = (LANEID+1)&63
else if (DPP_CTRL==DPP_WF_RR1)
    srcLane = (LANEID-1)&63
else if (DPP_CTRL==DPP_ROW_MIRROR)
{
    BYTE curR = LANEID&~15
    srcLane = curR + ((LANEID&15)^15)
}
else if (DPP_CTRL==DPP_ROW_HALF_MIRROR)
{
    BYTE curR = LANEID&~7
    srcLane = curR + ((LANEID&7)^7)
}
else if (DPP_CTRL==DPP_BCAST_15)
{
    BYTE curR = LANEID&~15
    if (LANEID<15)
        srcLane = LANEID
    else
        srcLane = ((LANEID-16)&~15)+15
}
else if (DPP_CTRL==DPP_BCAST_31)
{
    BYTE curR = LANEID&~31
    if (LANEID<31)
        srcLane = LANEID
    else
        srcLane = ((LANEID-31)&~31)+31
}
if (srcLane < LANESNUM)
    SRC0_DST[LANEID] = SRC0_SRC[srcLane]
else if (BOUND_CTRL==0)
    SRC0_DST[LANEID] = 0
else
    invalid = 1
if ((ROW_MASK & (1U<<(LANEID>>4)))==0)
    invalid = 1
if ((BANK_MASK & (1U<<((LANEID>>2)&3)))==0)
    invalid = 1
if (!invalid)
    VDST = OPERATION(SRC0_DST,SRC1)
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