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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. 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	CLRX 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	CLRX 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).

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 if (HAVE_SRC0) { 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_1: 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_1: 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,SRC1) 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; }