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luau/CodeGen/include/Luau/AssemblyBuilderA64.h
Arseny Kapoulkine 9aa82c6fb9
CodeGen: Improve lowering of NUM_TO_VEC on A64 for constants (#1194) 
When the input is a constant, we use a fairly inefficient sequence of
fmov+fcvt+dup or, when the double isn't encodable in fmov,
adr+ldr+fcvt+dup.

Instead, we can use the same lowering as X64 when the input is a
constant, and load the vector from memory. However, if the constant is
encodable via fmov, we can use a vector fmov instead (which is just one
instruction and doesn't need constant space).

Fortunately the bit encoding of fmov for 32-bit floating point numbers
matches that of 64-bit: the decoding algorithm is a little different
because it expands into a larger exponent, but the values are
compatible, so if a double can be encoded into a scalar fmov with a
given abcdefgh pattern, the same pattern should encode the same float;
due to the very limited number of mantissa and exponent bits, all values
that are encodable are also exact in both 32-bit and 64-bit floats.

This strategy is ~same as what gcc uses. For complex vectors, we
previously used 4 instructions and 8 bytes of constant storage, and now
we use 2 instructions and 16 bytes of constant storage, so the memory
footprint is the same; for simple vectors we just need 1 instruction (4
bytes).

clang lowers vector constants a little differently, opting to synthesize
a 64-bit integer using 4 instructions (mov/movk) and then move it to the
vector register - this requires 5 instructions and 20 bytes, vs ours/gcc
2 instructions and 8+16=24 bytes. I tried a simpler version of this that
would be more compact - synthesize a 32-bit integer constant with
mov+movk, and move it to vector register via dup.4s - but this was a
little slower on M2, so for now we prefer the slightly larger version as
it's not a regression vs current implementation.

On the vector approximation benchmark we get:

- Before this PR (flag=false): ~7.85 ns/op
- After this PR (flag=true): ~7.74 ns/op
- After this PR, with 0.125 instead of 0.123 in the benchmark code (to
use fmov): ~7.52 ns/op
- Not part of this PR, but the mov/dup strategy described above: ~8.00
ns/op
2024-03-13 12:56:11 -07:00

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// This file is part of the Luau programming language and is licensed under MIT License; see LICENSE.txt for details
#pragma once
#include "Luau/RegisterA64.h"
#include "Luau/AddressA64.h"
#include "Luau/ConditionA64.h"
#include "Luau/Label.h"
#include <string>
#include <vector>
namespace Luau
{
namespace CodeGen
{
namespace A64
{
enum FeaturesA64
{
Feature_JSCVT = 1 << 0,
};
class AssemblyBuilderA64
{
public:
explicit AssemblyBuilderA64(bool logText, unsigned int features = 0);
~AssemblyBuilderA64();
// Moves
void mov(RegisterA64 dst, RegisterA64 src);
void mov(RegisterA64 dst, int src); // macro
// Moves of 32-bit immediates get decomposed into one or more of these
void movz(RegisterA64 dst, uint16_t src, int shift = 0);
void movn(RegisterA64 dst, uint16_t src, int shift = 0);
void movk(RegisterA64 dst, uint16_t src, int shift = 0);
// Arithmetics
void add(RegisterA64 dst, RegisterA64 src1, RegisterA64 src2, int shift = 0);
void add(RegisterA64 dst, RegisterA64 src1, uint16_t src2);
void sub(RegisterA64 dst, RegisterA64 src1, RegisterA64 src2, int shift = 0);
void sub(RegisterA64 dst, RegisterA64 src1, uint16_t src2);
void neg(RegisterA64 dst, RegisterA64 src);
// Comparisons
// Note: some arithmetic instructions also have versions that update flags (ADDS etc) but we aren't using them atm
void cmp(RegisterA64 src1, RegisterA64 src2);
void cmp(RegisterA64 src1, uint16_t src2);
void csel(RegisterA64 dst, RegisterA64 src1, RegisterA64 src2, ConditionA64 cond);
void cset(RegisterA64 dst, ConditionA64 cond);
// Bitwise
void and_(RegisterA64 dst, RegisterA64 src1, RegisterA64 src2, int shift = 0);
void orr(RegisterA64 dst, RegisterA64 src1, RegisterA64 src2, int shift = 0);
void eor(RegisterA64 dst, RegisterA64 src1, RegisterA64 src2, int shift = 0);
void bic(RegisterA64 dst, RegisterA64 src1, RegisterA64 src2, int shift = 0);
void tst(RegisterA64 src1, RegisterA64 src2, int shift = 0);
void mvn_(RegisterA64 dst, RegisterA64 src);
// Bitwise with immediate
// Note: immediate must have a single contiguous sequence of 1 bits set of length 1..31
void and_(RegisterA64 dst, RegisterA64 src1, uint32_t src2);
void orr(RegisterA64 dst, RegisterA64 src1, uint32_t src2);
void eor(RegisterA64 dst, RegisterA64 src1, uint32_t src2);
void tst(RegisterA64 src1, uint32_t src2);
// Shifts
void lsl(RegisterA64 dst, RegisterA64 src1, RegisterA64 src2);
void lsr(RegisterA64 dst, RegisterA64 src1, RegisterA64 src2);
void asr(RegisterA64 dst, RegisterA64 src1, RegisterA64 src2);
void ror(RegisterA64 dst, RegisterA64 src1, RegisterA64 src2);
void clz(RegisterA64 dst, RegisterA64 src);
void rbit(RegisterA64 dst, RegisterA64 src);
void rev(RegisterA64 dst, RegisterA64 src);
// Shifts with immediates
// Note: immediate value must be in [0, 31] or [0, 63] range based on register type
void lsl(RegisterA64 dst, RegisterA64 src1, uint8_t src2);
void lsr(RegisterA64 dst, RegisterA64 src1, uint8_t src2);
void asr(RegisterA64 dst, RegisterA64 src1, uint8_t src2);
void ror(RegisterA64 dst, RegisterA64 src1, uint8_t src2);
// Bitfields
void ubfiz(RegisterA64 dst, RegisterA64 src, uint8_t f, uint8_t w);
void ubfx(RegisterA64 dst, RegisterA64 src, uint8_t f, uint8_t w);
void sbfiz(RegisterA64 dst, RegisterA64 src, uint8_t f, uint8_t w);
void sbfx(RegisterA64 dst, RegisterA64 src, uint8_t f, uint8_t w);
// Load
// Note: paired loads are currently omitted for simplicity
void ldr(RegisterA64 dst, AddressA64 src);
void ldrb(RegisterA64 dst, AddressA64 src);
void ldrh(RegisterA64 dst, AddressA64 src);
void ldrsb(RegisterA64 dst, AddressA64 src);
void ldrsh(RegisterA64 dst, AddressA64 src);
void ldrsw(RegisterA64 dst, AddressA64 src);
void ldp(RegisterA64 dst1, RegisterA64 dst2, AddressA64 src);
// Store
void str(RegisterA64 src, AddressA64 dst);
void strb(RegisterA64 src, AddressA64 dst);
void strh(RegisterA64 src, AddressA64 dst);
void stp(RegisterA64 src1, RegisterA64 src2, AddressA64 dst);
// Control flow
void b(Label& label);
void bl(Label& label);
void br(RegisterA64 src);
void blr(RegisterA64 src);
void ret();
// Conditional control flow
void b(ConditionA64 cond, Label& label);
void cbz(RegisterA64 src, Label& label);
void cbnz(RegisterA64 src, Label& label);
void tbz(RegisterA64 src, uint8_t bit, Label& label);
void tbnz(RegisterA64 src, uint8_t bit, Label& label);
// Address of embedded data
void adr(RegisterA64 dst, const void* ptr, size_t size);
void adr(RegisterA64 dst, uint64_t value);
void adr(RegisterA64 dst, double value);
// Address of code (label)
void adr(RegisterA64 dst, Label& label);
// Floating-point scalar/vector moves
// Note: constant must be compatible with immediate floating point moves (see isFmovSupported)
void fmov(RegisterA64 dst, RegisterA64 src);
void fmov(RegisterA64 dst, double src);
// Floating-point scalar/vector math
void fabs(RegisterA64 dst, RegisterA64 src);
void fadd(RegisterA64 dst, RegisterA64 src1, RegisterA64 src2);
void fdiv(RegisterA64 dst, RegisterA64 src1, RegisterA64 src2);
void fmul(RegisterA64 dst, RegisterA64 src1, RegisterA64 src2);
void fneg(RegisterA64 dst, RegisterA64 src);
void fsqrt(RegisterA64 dst, RegisterA64 src);
void fsub(RegisterA64 dst, RegisterA64 src1, RegisterA64 src2);
// Vector component manipulation
void ins_4s(RegisterA64 dst, RegisterA64 src, uint8_t index);
void ins_4s(RegisterA64 dst, uint8_t dstIndex, RegisterA64 src, uint8_t srcIndex);
void dup_4s(RegisterA64 dst, RegisterA64 src, uint8_t index);
// Floating-point rounding and conversions
void frinta(RegisterA64 dst, RegisterA64 src);
void frintm(RegisterA64 dst, RegisterA64 src);
void frintp(RegisterA64 dst, RegisterA64 src);
void fcvt(RegisterA64 dst, RegisterA64 src);
void fcvtzs(RegisterA64 dst, RegisterA64 src);
void fcvtzu(RegisterA64 dst, RegisterA64 src);
void scvtf(RegisterA64 dst, RegisterA64 src);
void ucvtf(RegisterA64 dst, RegisterA64 src);
// Floating-point conversion to integer using JS rules (wrap around 2^32) and set Z flag
// note: this is part of ARM8.3 (JSCVT feature); support of this instruction needs to be checked at runtime
void fjcvtzs(RegisterA64 dst, RegisterA64 src);
// Floating-point comparisons
void fcmp(RegisterA64 src1, RegisterA64 src2);
void fcmpz(RegisterA64 src);
void fcsel(RegisterA64 dst, RegisterA64 src1, RegisterA64 src2, ConditionA64 cond);
void udf();
// Run final checks
bool finalize();
// Places a label at current location and returns it
Label setLabel();
// Assigns label position to the current location
void setLabel(Label& label);
// Extracts code offset (in bytes) from label
uint32_t getLabelOffset(const Label& label)
{
CODEGEN_ASSERT(label.location != ~0u);
return label.location * 4;
}
void logAppend(const char* fmt, ...) LUAU_PRINTF_ATTR(2, 3);
uint32_t getCodeSize() const;
unsigned getInstructionCount() const;
// Resulting data and code that need to be copied over one after the other
// The *end* of 'data' has to be aligned to 16 bytes, this will also align 'code'
std::vector<uint8_t> data;
std::vector<uint32_t> code;
std::string text;
const bool logText = false;
const unsigned int features = 0;
// Maximum immediate argument to functions like add/sub/cmp
static constexpr size_t kMaxImmediate = (1 << 12) - 1;
// Check if immediate mode mask is supported for bitwise operations (and/or/xor)
static bool isMaskSupported(uint32_t mask);
// Check if fmov can be used to synthesize a constant
static bool isFmovSupported(double value);
private:
// Instruction archetypes
void place0(const char* name, uint32_t word);
void placeSR3(const char* name, RegisterA64 dst, RegisterA64 src1, RegisterA64 src2, uint8_t op, int shift = 0, int N = 0);
void placeSR2(const char* name, RegisterA64 dst, RegisterA64 src, uint8_t op, uint8_t op2 = 0);
void placeR3(const char* name, RegisterA64 dst, RegisterA64 src1, RegisterA64 src2, uint8_t op, uint8_t op2);
void placeR1(const char* name, RegisterA64 dst, RegisterA64 src, uint32_t op);
void placeI12(const char* name, RegisterA64 dst, RegisterA64 src1, int src2, uint8_t op);
void placeI16(const char* name, RegisterA64 dst, int src, uint8_t op, int shift = 0);
void placeA(const char* name, RegisterA64 dst, AddressA64 src, uint16_t opsize, int sizelog);
void placeB(const char* name, Label& label, uint8_t op);
void placeBC(const char* name, Label& label, uint8_t op, uint8_t cond);
void placeBCR(const char* name, Label& label, uint8_t op, RegisterA64 cond);
void placeBR(const char* name, RegisterA64 src, uint32_t op);
void placeBTR(const char* name, Label& label, uint8_t op, RegisterA64 cond, uint8_t bit);
void placeADR(const char* name, RegisterA64 src, uint8_t op);
void placeADR(const char* name, RegisterA64 src, uint8_t op, Label& label);
void placeP(const char* name, RegisterA64 dst1, RegisterA64 dst2, AddressA64 src, uint8_t op, uint8_t opc, int sizelog);
void placeCS(const char* name, RegisterA64 dst, RegisterA64 src1, RegisterA64 src2, ConditionA64 cond, uint8_t op, uint8_t opc, int invert = 0);
void placeFCMP(const char* name, RegisterA64 src1, RegisterA64 src2, uint8_t op, uint8_t opc);
void placeFMOV(const char* name, RegisterA64 dst, double src, uint32_t op);
void placeBM(const char* name, RegisterA64 dst, RegisterA64 src1, uint32_t src2, uint8_t op);
void placeBFM(const char* name, RegisterA64 dst, RegisterA64 src1, int src2, uint8_t op, int immr, int imms);
void placeER(const char* name, RegisterA64 dst, RegisterA64 src1, RegisterA64 src2, uint8_t op, int shift);
void placeVR(const char* name, RegisterA64 dst, RegisterA64 src1, RegisterA64 src2, uint16_t op, uint8_t op2);
void place(uint32_t word);
struct Patch
{
enum Kind
{
Imm26,
Imm19,
Imm14,
};
Kind kind : 2;
uint32_t label : 30;
uint32_t location;
};
void patchLabel(Label& label, Patch::Kind kind);
void patchOffset(uint32_t location, int value, Patch::Kind kind);
void commit();
LUAU_NOINLINE void extend();
// Data
size_t allocateData(size_t size, size_t align);
// Logging of assembly in text form
LUAU_NOINLINE void log(const char* opcode);
LUAU_NOINLINE void log(const char* opcode, RegisterA64 dst, RegisterA64 src1, RegisterA64 src2, int shift = 0);
LUAU_NOINLINE void log(const char* opcode, RegisterA64 dst, RegisterA64 src1, int src2);
LUAU_NOINLINE void log(const char* opcode, RegisterA64 dst, RegisterA64 src);
LUAU_NOINLINE void log(const char* opcode, RegisterA64 dst, int src, int shift = 0);
LUAU_NOINLINE void log(const char* opcode, RegisterA64 dst, double src);
LUAU_NOINLINE void log(const char* opcode, RegisterA64 dst, AddressA64 src);
LUAU_NOINLINE void log(const char* opcode, RegisterA64 dst1, RegisterA64 dst2, AddressA64 src);
LUAU_NOINLINE void log(const char* opcode, RegisterA64 src, Label label, int imm = -1);
LUAU_NOINLINE void log(const char* opcode, RegisterA64 src);
LUAU_NOINLINE void log(const char* opcode, Label label);
LUAU_NOINLINE void log(const char* opcode, RegisterA64 dst, RegisterA64 src1, RegisterA64 src2, ConditionA64 cond);
LUAU_NOINLINE void log(Label label);
LUAU_NOINLINE void log(RegisterA64 reg);
LUAU_NOINLINE void log(AddressA64 addr);
uint32_t nextLabel = 1;
std::vector<Patch> pendingLabels;
std::vector<uint32_t> labelLocations;
bool finalized = false;
bool overflowed = false;
size_t dataPos = 0;
uint32_t* codePos = nullptr;
uint32_t* codeEnd = nullptr;
};
} // namespace A64
} // namespace CodeGen
} // namespace Luau
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