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DRAFT: Shady VM early start.
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@kannanvijayan
kannanvijayan committed Nov 10, 2023
1 parent b7c8563 commit 5c9863a
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264 changes: 192 additions & 72 deletions src/gpu/compute/commands/wgsl_library/shady_vm.wgsl
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Original file line number Diff line number Diff line change
Expand Up @@ -7,15 +7,17 @@
*
* ```
* Register file:
* r0-r31: 32 x 32-bit registers
* r0-r29: 30 x 32-bit registers, read-write general purpose
* r30: 1 x 32-bit register, read-only, always zero
* r32-r79: 48 x 32-bit registers, only usable as source operands
* r80-r95: UNUSED
* r80-r96: UNUSED
*
* Special registers:
* r96: program counter
* r97: flags register
* r98: call stack depth
* r99-123: UNUSED
* r112: program counter
* r113: flags register
* r114: call stack depth
* r115: error code
* r116-123: UNUSED
*
* r124: call-stack register 3
* r125: call-stack register 2
Expand Down Expand Up @@ -92,7 +94,7 @@
* - 0 => all flags must be set, 1 => any flag must be set
* * KK (2 bits)
* - branch kind
* - 00 => goto, 01 => call, 10 => return
* - 00 => goto, 01 => call, 10 => return, 11 => end
* ```
*/

Expand Down Expand Up @@ -213,54 +215,109 @@ const SHADY_BCOP_INS_ARITH_KIND_DIV: u32 = 2u;
const SHADY_BCOP_INS_ARITH_KIND_MOD: u32 = 3u;

/** Immediate instruction kinds. */
const SHADY_BCOP_INS_IMMED_KIND_SET = 0u;
const SHADY_BCOP_INS_IMMED_KIND_XOR = 1u;
const SHADY_BCOP_INS_IMMED_KIND_AND = 2u;
const SHADY_BCOP_INS_IMMED_KIND_OR = 3u;
const SHADY_BCOP_INS_IMMED_KIND_SET: u32 = 0u;
const SHADY_BCOP_INS_IMMED_KIND_XOR: u32 = 1u;
const SHADY_BCOP_INS_IMMED_KIND_AND: u32 = 2u;
const SHADY_BCOP_INS_IMMED_KIND_OR: u32 = 3u;

/** Control flow instruction kinds. */
const SHADY_BCOP_INS_CFLOW_KIND_GOTO = 0u;
const SHADY_BCOP_INS_CFLOW_KIND_CALL = 1u;
const SHADY_BCOP_INS_CFLOW_KIND_RET = 2u;
const SHADY_BCOP_INS_CFLOW_KIND_GOTO: u32 = 0u;
const SHADY_BCOP_INS_CFLOW_KIND_CALL: u32 = 1u;
const SHADY_BCOP_INS_CFLOW_KIND_RET: u32 = 2u;
const SHADY_BCOP_INS_CFLOW_KIND_END: u32 = 3u;

/** Flags query kinds. */
const SHADY_BCOP_CFLOW_QUERY_ALL: u32 = 0u;
const SHADY_BCOP_CFLOW_QUERY_ANY: u32 = 1u;

/** Flags bit meanings. */
const SHADY_BCOP_FLAGS_BIT_ZERO: u32 = 1u;
const SHADY_BCOP_FLAGS_BIT_NEGATIVE: u32 = 2u;
const SHADY_BCOP_FLAGS_BIT_POSITIVE: u32 = 4u;
const SHADY_BCOP_FLAGS_BIT_HIGH: u32 = 8u;
const SHADY_BCOP_FLAGS_BIT_ALWAYS: u32 = 16u;

/** Offsets of special registers. */
const SHADY_REG_OFFSET_PC: u32 = 96u;
const SHADY_REG_OFFSET_FL: u32 = 97u;
const SHADY_REG_OFFSET_CD: u32 = 98u;
const SHADY_REG_OFFSET_EC: u32 = 99u;

/** Start offset of the call stack. (callstack grows down) */
const SHADY_CALLSTACK_OFFSET: u32 = 127u;
const SHADY_CALLDEPTH_MAX: u32 = 4u;

/** Error codes. */
const SHADY_EC_NONE: u32 = 0u;
const SHADY_EC_INVALID_INSTRUCTION: u32 = 1u;
const SHADY_EC_CALLSTACK_OVERFLOW: u32 = 2u;
const SHADY_EC_CALLSTACK_UNDERFLOW: u32 = 3u;
const SHADY_EC_SANITY: u32 = 4u;

/** PC that marks the end of the program. */
const SHADY_PC_END: u32 = 0xFFFFFFFFu;


/** Access to the register file and call stack. */
struct ShadyRegistersAndCallStack {
regs: array<u32, 120>,
callstack: array<u32, 8>,
struct ShadyRegisterFile {
regs: array<u32, 128>,
}

/** Initialize private pointers from a pointer to the full struct. */
fn shady_init_ptrs(
regfile: ptr<private, ShadyRegisterFile>,
flags: ptr<private, u32>,
pc: ptr<private, u32>,
cd: ptr<private, u32>
) {
*flags = (*regfile).regs[SHADY_REG_OFFSET_FL];
*pc = (*regfile).regs[SHADY_REG_OFFSET_PC];
*cd = (*regfile).regs[SHADY_REG_OFFSET_CD];
}

/** Update register file struct. */
fn shady_writeback_ptrs(
regfile: ptr<private, ShadyRegisterFile>,
flags: ptr<private, u32>,
pc: ptr<private, u32>,
cd: ptr<private, u32>
) {
(*regfile).regs[SHADY_REG_OFFSET_FL] = *flags;
(*regfile).regs[SHADY_REG_OFFSET_PC] = *pc;
(*regfile).regs[SHADY_REG_OFFSET_CD] = *cd;
}

/** Execute an instruction. */
fn shady_ins_exec(
ins: u32,
regs: ptr<private, ShadyRegistersAndCallStack>,
regfile: ptr<private, ShadyRegisterFile>,
flags: ptr<private, u32>,
pc: ptr<private, u32>
) {
pc: ptr<private, u32>,
cd: ptr<private, u32>
) -> u32 {
let fam = shady_bcop_ins_get_insfam(ins);
let kind = shady_bcop_ins_get_kind(ins);
switch fam {
case 1u: {
shady_ins_exec_arith(ins, kind, regs, flags, pc);
}
case 2u: {
shady_ins_exec_immed(ins, kind, regs, flags, pc);
}
case 3u: {
shady_ins_exec_cflow(ins, kind, regs, flags, pc);
}
default: {
}
if fam == SHADY_BCOP_INS_ARITH {
return shady_ins_exec_arith(ins, kind, regfile, flags, pc);
}
if fam == SHADY_BCOP_INS_IMMED {
return shady_ins_exec_immed(ins, kind, regfile, flags, pc);
}
if fam == SHADY_BCOP_INS_CFLOW {
return shady_ins_exec_cflow(ins, kind, regfile, flags, pc, cd);
}
// Unrecognized instruction family.
return set_error_and_end(regfile, SHADY_EC_INVALID_INSTRUCTION);
}

/** Execute an arithmetic instruction. */
fn shady_ins_exec_arith(
ins: u32,
kind: u32,
regs: ptr<private, ShadyRegistersAndCallStack>,
regfile: ptr<private, ShadyRegisterFile>,
flags: ptr<private, u32>,
pc: ptr<private, u32>
) {
) -> u32 {
let srcreg1 = shady_bcop_ins_get_srcreg1(ins);
let srcreg2 = shady_bcop_ins_get_srcreg2(ins);
let srcreg2_shift = shady_bcop_ins_get_srcrsh(ins);
Expand All @@ -273,9 +330,9 @@ fn shady_ins_exec_arith(
let flip = shady_bcop_ins_get_flip(ins);
let dstreg = shady_bcop_ins_get_dstreg(ins);

var srcval1 = (*regs)[srcreg1];
var srcval1 = (*regfile).regs[srcreg1];

var srcval2 = (*regs)[srcreg2];
var srcval2 = (*regfile).regs[srcreg2];
// Shift and mask.
srcval2 = (srcval2 >> srcreg2_shift_bits) & srcreg2_mask_val;
// Use the high-bit to sign extend.
Expand All @@ -297,31 +354,35 @@ fn shady_ins_exec_arith(
}

var result = 0u;
switch kind {
case 0u: {
result = srcval1 + srcval2;
}
case 1u: {
result = srcval1 * srcval2;
}
case 2u: {
result = srcval1 / srcval2;
}
default: {
result = srcval1 % srcval2;
}
if kind == SHADY_BCOP_INS_ARITH_KIND_ADD {
result = srcval1 + srcval2;
} else if kind == SHADY_BCOP_INS_ARITH_KIND_MUL {
result = srcval1 * srcval2;
} else if kind == SHADY_BCOP_INS_ARITH_KIND_DIV {
result = srcval1 / srcval2;
} else if kind == SHADY_BCOP_INS_ARITH_KIND_MOD {
result = srcval1 % srcval2;
} else {
// Should never get here because of the instruction kind mask.
return set_error_and_end(regfile, SHADY_EC_SANITY);
}
(*regs)[dstreg] = result;
(*regfile).regs[dstreg] = result;

// Update flags.
*flags = calculate_flags_word(result);

// Go to next instruction.
return *pc + 1u;
}

/** Execute an immediate instruction. */
fn shady_ins_exec_immed(
ins: u32,
kind: u32,
regs: ptr<private, ShadyRegistersAndCallStack>,
regfile: ptr<private, ShadyRegisterFile>,
flags: ptr<private, u32>,
pc: ptr<private, u32>
) {
) -> u32 {
var immval = shady_bcop_ins_get_immval(ins);
let immval_sx = shady_bcop_ins_get_sx(ins);
let immlsh = shady_bcop_ins_get_immlsh(ins);
Expand All @@ -335,32 +396,37 @@ fn shady_ins_exec_immed(
let immlsh_bits = immlsh << 2u;
immval = immval << immlsh_bits;

var result = (*regs)[dstreg];
switch kind {
case 0u: {
result = immval;
}
case 1u: {
result = result ^ immval;
}
case 2u: {
result = result & immval;
}
default: {
result = result | immval;
}
var result = (*regfile).regs[dstreg];
if kind == SHADY_BCOP_INS_IMMED_KIND_SET {
result = immval;
} else if kind == SHADY_BCOP_INS_IMMED_KIND_XOR {
result = result ^ immval;
} else if kind == SHADY_BCOP_INS_IMMED_KIND_AND {
result = result & immval;
} else if kind == SHADY_BCOP_INS_IMMED_KIND_OR {
result = result | immval;
} else {
// Should never get here because of the instruction kind mask.
return set_error_and_end(regfile, SHADY_EC_SANITY);
}
(*regs)[dstreg] = result;
(*regfile).regs[dstreg] = result;

// Update flags.
*flags = calculate_flags_word(result);

// Go to next instruction.
return *pc + 1u;
}

/** Execute a control flow instruction. */
fn shady_ins_exec_cflow(
ins: u32,
kind: u32,
regs: ptr<private, ShadyRegistersAndCallStack>,
regfile: ptr<private, ShadyRegisterFile>,
flags: ptr<private, u32>,
pc: ptr<private, u32>
) {
pc: ptr<private, u32>,
cd: ptr<private, u32>
) -> u32 {
let brtarg = shady_bcop_ins_get_brtarg(ins);
let chk_flags = shady_bcop_ins_get_brflags(ins);
let query = shady_bcop_ins_get_brquery(ins);
Expand All @@ -370,11 +436,65 @@ fn shady_ins_exec_cflow(
let flags_set_all = flags_set == chk_flags;
let flags_set_any = flags_set > 0u;
var do_branch = false;
if query == 0u {
if query == SHADY_BCOP_CFLOW_QUERY_ALL {
do_branch = flags_set_all;
} else {
do_branch = flags_set_any;
}

// TODO: implement.
if ! do_branch {
return *pc + 1u;
}

if kind == SHADY_BCOP_INS_CFLOW_KIND_GOTO {
return brtarg;
}
if kind == SHADY_BCOP_INS_CFLOW_KIND_CALL {
let cd_val = *cd;
if cd_val >= SHADY_CALLDEPTH_MAX {
return set_error_and_end(regfile, SHADY_EC_CALLSTACK_OVERFLOW);
}
(*regfile).regs[SHADY_CALLSTACK_OFFSET - cd_val] = *pc + 1u;
*cd = cd_val + 1u;
return brtarg;
}
if kind == SHADY_BCOP_INS_CFLOW_KIND_RET {
let cd_val = *cd;
if cd_val == 0u {
return set_error_and_end(regfile, SHADY_EC_CALLSTACK_UNDERFLOW);
}
let ret_pc = (*regfile).regs[SHADY_CALLSTACK_OFFSET - cd_val];
*cd = cd_val - 1u;
return ret_pc;
}
if kind == SHADY_BCOP_INS_CFLOW_KIND_END {
return SHADY_PC_END;
}
// Should never get here because of the instruction kind mask.
return set_error_and_end(regfile, SHADY_EC_SANITY);
}

fn calculate_flags_word(value: u32) -> u32 {
var flags = SHADY_BCOP_FLAGS_BIT_ALWAYS;
if value == 0u {
flags |= SHADY_BCOP_FLAGS_BIT_ZERO;
}
if value > 0u {
flags |= SHADY_BCOP_FLAGS_BIT_POSITIVE;
}
if value < 0u {
flags |= SHADY_BCOP_FLAGS_BIT_NEGATIVE;
}
if (value >> 31u) > 0u {
flags |= SHADY_BCOP_FLAGS_BIT_HIGH;
}
return flags;
}

fn set_error_and_end(
regfile: ptr<private, ShadyRegisterFile>,
err: u32,
) -> u32 {
(*regfile).regs[SHADY_REG_OFFSET_EC] = err;
return SHADY_PC_END;
}
2 changes: 2 additions & 0 deletions src/gpu/mod.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -11,6 +11,8 @@ mod map_buffer;
mod seq_buffer;
mod world;

mod shady_vm;

pub(crate) mod compute;
pub(crate) use self::{
constants::{ GPU_MIN_BUFFER_SIZE, GPU_COPY_BUFFER_ALIGNMENT },
Expand Down
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