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emitxarch.cpp
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emitxarch.cpp
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// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
/*XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
XX XX
XX emitX86.cpp XX
XX XX
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
*/
#include "jitpch.h"
#ifdef _MSC_VER
#pragma hdrstop
#endif
#if defined(TARGET_XARCH)
/*****************************************************************************/
/*****************************************************************************/
#include "instr.h"
#include "emit.h"
#include "codegen.h"
bool IsSSEInstruction(instruction ins)
{
return (ins >= INS_FIRST_SSE_INSTRUCTION) && (ins <= INS_LAST_SSE_INSTRUCTION);
}
bool IsSSEOrAVXInstruction(instruction ins)
{
return (ins >= INS_FIRST_SSE_INSTRUCTION) && (ins <= INS_LAST_AVX_INSTRUCTION);
}
bool IsAVXOnlyInstruction(instruction ins)
{
return (ins >= INS_FIRST_AVX_INSTRUCTION) && (ins <= INS_LAST_AVX_INSTRUCTION);
}
bool IsFMAInstruction(instruction ins)
{
return (ins >= INS_FIRST_FMA_INSTRUCTION) && (ins <= INS_LAST_FMA_INSTRUCTION);
}
bool IsBMIInstruction(instruction ins)
{
return (ins >= INS_FIRST_BMI_INSTRUCTION) && (ins <= INS_LAST_BMI_INSTRUCTION);
}
regNumber getBmiRegNumber(instruction ins)
{
switch (ins)
{
case INS_blsi:
{
return (regNumber)3;
}
case INS_blsmsk:
{
return (regNumber)2;
}
case INS_blsr:
{
return (regNumber)1;
}
default:
{
assert(IsBMIInstruction(ins));
return REG_NA;
}
}
}
regNumber getSseShiftRegNumber(instruction ins)
{
switch (ins)
{
case INS_psrldq:
{
return (regNumber)3;
}
case INS_pslldq:
{
return (regNumber)7;
}
case INS_psrld:
case INS_psrlw:
case INS_psrlq:
{
return (regNumber)2;
}
case INS_pslld:
case INS_psllw:
case INS_psllq:
{
return (regNumber)6;
}
case INS_psrad:
case INS_psraw:
{
return (regNumber)4;
}
default:
{
assert(!"Invalid instruction for SSE2 instruction of the form: opcode reg, immed8");
return REG_NA;
}
}
}
bool emitter::IsAVXInstruction(instruction ins)
{
return UseVEXEncoding() && IsSSEOrAVXInstruction(ins);
}
// Returns true if the AVX instruction is a binary operator that requires 3 operands.
// When we emit an instruction with only two operands, we will duplicate the destination
// as a source.
// TODO-XArch-Cleanup: This is a temporary solution for now. Eventually this needs to
// be formalized by adding an additional field to instruction table to
// to indicate whether a 3-operand instruction.
bool emitter::IsDstDstSrcAVXInstruction(instruction ins)
{
return ((CodeGenInterface::instInfo[ins] & INS_Flags_IsDstDstSrcAVXInstruction) != 0) && IsAVXInstruction(ins);
}
// Returns true if the AVX instruction requires 3 operands that duplicate the source
// register in the vvvv field.
// TODO-XArch-Cleanup: This is a temporary solution for now. Eventually this needs to
// be formalized by adding an additional field to instruction table to
// to indicate whether a 3-operand instruction.
bool emitter::IsDstSrcSrcAVXInstruction(instruction ins)
{
return ((CodeGenInterface::instInfo[ins] & INS_Flags_IsDstSrcSrcAVXInstruction) != 0) && IsAVXInstruction(ins);
}
//------------------------------------------------------------------------
// AreUpper32BitsZero: check if some previously emitted
// instruction set the upper 32 bits of reg to zero.
//
// Arguments:
// reg - register of interest
//
// Return Value:
// true if previous instruction zeroed reg's upper 32 bits.
// false if it did not, or if we can't safely determine.
//
// Notes:
// Currently only looks back one instruction.
//
// movsx eax, ... might seem viable but we always encode this
// instruction with a 64 bit destination. See TakesRexWPrefix.
bool emitter::AreUpper32BitsZero(regNumber reg)
{
// If there are no instructions in this IG, we can look back at
// the previous IG's instructions if this IG is an extension.
//
if ((emitCurIGinsCnt == 0) && ((emitCurIG->igFlags & IGF_EXTEND) == 0))
{
return false;
}
instrDesc* id = emitLastIns;
insFormat fmt = id->idInsFmt();
// This isn't meant to be a comprehensive check. Just look for what
// seems to be common.
switch (fmt)
{
case IF_RWR_CNS:
case IF_RRW_CNS:
case IF_RRW_SHF:
case IF_RWR_RRD:
case IF_RRW_RRD:
case IF_RWR_MRD:
case IF_RWR_SRD:
case IF_RWR_ARD:
// Bail if not writing to the right register
if (id->idReg1() != reg)
{
return false;
}
// Bail if movsx, we always have movsx sign extend to 8 bytes
if (id->idIns() == INS_movsx)
{
return false;
}
// movzx always zeroes the upper 32 bits.
if (id->idIns() == INS_movzx)
{
return true;
}
// Else rely on operation size.
return (id->idOpSize() == EA_4BYTE);
default:
break;
}
return false;
}
//------------------------------------------------------------------------
// AreFlagsSetToZeroCmp: Checks if the previous instruction set the SZ, and optionally OC, flags to
// the same values as if there were a compare to 0
//
// Arguments:
// reg - register of interest
// opSize - size of register
// needsOCFlags - additionally check the overflow and carry flags
//
// Return Value:
// true if the previous instruction set the flags for reg
// false if not, or if we can't safely determine
//
// Notes:
// Currently only looks back one instruction.
bool emitter::AreFlagsSetToZeroCmp(regNumber reg, emitAttr opSize, bool needsOCFlags)
{
assert(reg != REG_NA);
// Don't look back across IG boundaries (possible control flow)
if (emitCurIGinsCnt == 0 && ((emitCurIG->igFlags & IGF_EXTEND) == 0))
{
return false;
}
instrDesc* id = emitLastIns;
insFormat fmt = id->idInsFmt();
// make sure op1 is a reg
switch (fmt)
{
case IF_RWR_CNS:
case IF_RRW_CNS:
case IF_RRW_SHF:
case IF_RWR_RRD:
case IF_RRW_RRD:
case IF_RWR_MRD:
case IF_RWR_SRD:
case IF_RRW_SRD:
case IF_RWR_ARD:
case IF_RRW_ARD:
case IF_RWR:
case IF_RRD:
case IF_RRW:
break;
default:
return false;
}
if (id->idReg1() != reg)
{
return false;
}
switch (id->idIns())
{
case INS_adc:
case INS_add:
case INS_dec:
case INS_dec_l:
case INS_inc:
case INS_inc_l:
case INS_neg:
case INS_shr_1:
case INS_shl_1:
case INS_sar_1:
case INS_sbb:
case INS_sub:
case INS_xadd:
if (needsOCFlags)
{
return false;
}
FALLTHROUGH;
// these always set OC to 0
case INS_and:
case INS_or:
case INS_xor:
return id->idOpSize() == opSize;
default:
break;
}
return false;
}
//------------------------------------------------------------------------
// IsDstSrcImmAvxInstruction: Checks if the instruction has a "reg, reg/mem, imm" or
// "reg/mem, reg, imm" form for the legacy, VEX, and EVEX
// encodings.
//
// Arguments:
// instruction -- processor instruction to check
//
// Return Value:
// true if instruction has a "reg, reg/mem, imm" or "reg/mem, reg, imm" encoding
// form for the legacy, VEX, and EVEX encodings.
//
// That is, the instruction takes two operands, one of which is immediate, and it
// does not need to encode any data in the VEX.vvvv field.
//
static bool IsDstSrcImmAvxInstruction(instruction ins)
{
switch (ins)
{
case INS_aeskeygenassist:
case INS_extractps:
case INS_pextrb:
case INS_pextrw:
case INS_pextrd:
case INS_pextrq:
case INS_pshufd:
case INS_pshufhw:
case INS_pshuflw:
case INS_roundpd:
case INS_roundps:
return true;
default:
return false;
}
}
// -------------------------------------------------------------------
// Is4ByteSSEInstruction: Returns true if the SSE instruction is a 4-byte opcode.
//
// Arguments:
// ins - instruction
//
// Note that this should be true for any of the instructions in instrsXArch.h
// that use the SSE38 or SSE3A macro but returns false if the VEX encoding is
// in use, since that encoding does not require an additional byte.
bool emitter::Is4ByteSSEInstruction(instruction ins)
{
return !UseVEXEncoding() && EncodedBySSE38orSSE3A(ins);
}
// Returns true if this instruction requires a VEX prefix
// All AVX instructions require a VEX prefix
bool emitter::TakesVexPrefix(instruction ins)
{
// special case vzeroupper as it requires 2-byte VEX prefix
// special case the fencing, movnti and the prefetch instructions as they never take a VEX prefix
switch (ins)
{
case INS_lfence:
case INS_mfence:
case INS_movnti:
case INS_prefetchnta:
case INS_prefetcht0:
case INS_prefetcht1:
case INS_prefetcht2:
case INS_sfence:
case INS_vzeroupper:
return false;
default:
break;
}
return IsAVXInstruction(ins);
}
// Add base VEX prefix without setting W, R, X, or B bits
// L bit will be set based on emitter attr.
//
// 2-byte VEX prefix = C5 <R,vvvv,L,pp>
// 3-byte VEX prefix = C4 <R,X,B,m-mmmm> <W,vvvv,L,pp>
// - R, X, B, W - bits to express corresponding REX prefixes
// - m-mmmmm (5-bit)
// 0-00001 - implied leading 0F opcode byte
// 0-00010 - implied leading 0F 38 opcode bytes
// 0-00011 - implied leading 0F 3A opcode bytes
// Rest - reserved for future use and usage of them will uresult in Undefined instruction exception
//
// - vvvv (4-bits) - register specifier in 1's complement form; must be 1111 if unused
// - L - scalar or AVX-128 bit operations (L=0), 256-bit operations (L=1)
// - pp (2-bits) - opcode extension providing equivalent functionality of a SIMD size prefix
// these prefixes are treated mandatory when used with escape opcode 0Fh for
// some SIMD instructions
// 00 - None (0F - packed float)
// 01 - 66 (66 0F - packed double)
// 10 - F3 (F3 0F - scalar float
// 11 - F2 (F2 0F - scalar double)
#define DEFAULT_3BYTE_VEX_PREFIX 0xC4E07800000000ULL
#define DEFAULT_3BYTE_VEX_PREFIX_MASK 0xFFFFFF00000000ULL
#define LBIT_IN_3BYTE_VEX_PREFIX 0x00000400000000ULL
emitter::code_t emitter::AddVexPrefix(instruction ins, code_t code, emitAttr attr)
{
// The 2-byte VEX encoding is preferred when possible, but actually emitting
// it depends on a number of factors that we may not know until much later.
//
// In order to handle this "easily", we just carry the 3-byte encoding all
// the way through and "fix-up" the encoding when the VEX prefix is actually
// emitted, by simply checking that all the requirements were met.
// Only AVX instructions require VEX prefix
assert(IsAVXInstruction(ins));
// Shouldn't have already added VEX prefix
assert(!hasVexPrefix(code));
assert((code & DEFAULT_3BYTE_VEX_PREFIX_MASK) == 0);
code |= DEFAULT_3BYTE_VEX_PREFIX;
if (attr == EA_32BYTE)
{
// Set L bit to 1 in case of instructions that operate on 256-bits.
code |= LBIT_IN_3BYTE_VEX_PREFIX;
}
return code;
}
// Returns true if this instruction, for the given EA_SIZE(attr), will require a REX.W prefix
bool TakesRexWPrefix(instruction ins, emitAttr attr)
{
// Because the current implementation of AVX does not have a way to distinguish between the register
// size specification (128 vs. 256 bits) and the operand size specification (32 vs. 64 bits), where both are
// required, the instruction must be created with the register size attribute (EA_16BYTE or EA_32BYTE),
// and here we must special case these by the opcode.
switch (ins)
{
case INS_vpermpd:
case INS_vpermq:
case INS_vpsrlvq:
case INS_vpsllvq:
case INS_pinsrq:
case INS_pextrq:
case INS_vfmadd132pd:
case INS_vfmadd213pd:
case INS_vfmadd231pd:
case INS_vfmadd132sd:
case INS_vfmadd213sd:
case INS_vfmadd231sd:
case INS_vfmaddsub132pd:
case INS_vfmaddsub213pd:
case INS_vfmaddsub231pd:
case INS_vfmsubadd132pd:
case INS_vfmsubadd213pd:
case INS_vfmsubadd231pd:
case INS_vfmsub132pd:
case INS_vfmsub213pd:
case INS_vfmsub231pd:
case INS_vfmsub132sd:
case INS_vfmsub213sd:
case INS_vfmsub231sd:
case INS_vfnmadd132pd:
case INS_vfnmadd213pd:
case INS_vfnmadd231pd:
case INS_vfnmadd132sd:
case INS_vfnmadd213sd:
case INS_vfnmadd231sd:
case INS_vfnmsub132pd:
case INS_vfnmsub213pd:
case INS_vfnmsub231pd:
case INS_vfnmsub132sd:
case INS_vfnmsub213sd:
case INS_vfnmsub231sd:
case INS_vpmaskmovq:
case INS_vpgatherdq:
case INS_vpgatherqq:
case INS_vgatherdpd:
case INS_vgatherqpd:
return true;
default:
break;
}
#ifdef TARGET_AMD64
// movsx should always sign extend out to 8 bytes just because we don't track
// whether the dest should be 4 bytes or 8 bytes (attr indicates the size
// of the source, not the dest).
// A 4-byte movzx is equivalent to an 8 byte movzx, so it is not special
// cased here.
//
// Rex_jmp = jmp with rex prefix always requires rex.w prefix.
if (ins == INS_movsx || ins == INS_rex_jmp)
{
return true;
}
if (EA_SIZE(attr) != EA_8BYTE)
{
return false;
}
if (IsSSEOrAVXInstruction(ins))
{
switch (ins)
{
case INS_andn:
case INS_bextr:
case INS_blsi:
case INS_blsmsk:
case INS_blsr:
case INS_bzhi:
case INS_cvttsd2si:
case INS_cvttss2si:
case INS_cvtsd2si:
case INS_cvtss2si:
case INS_cvtsi2sd:
case INS_cvtsi2ss:
case INS_mov_xmm2i:
case INS_mov_i2xmm:
case INS_movnti:
case INS_mulx:
case INS_pdep:
case INS_pext:
case INS_rorx:
return true;
default:
return false;
}
}
// TODO-XArch-Cleanup: Better way to not emit REX.W when we don't need it, than just testing all these
// opcodes...
// These are all the instructions that default to 8-byte operand without the REX.W bit
// With 1 special case: movzx because the 4 byte version still zeros-out the hi 4 bytes
// so we never need it
if ((ins != INS_push) && (ins != INS_pop) && (ins != INS_movq) && (ins != INS_movzx) && (ins != INS_push_hide) &&
(ins != INS_pop_hide) && (ins != INS_ret) && (ins != INS_call) && !((ins >= INS_i_jmp) && (ins <= INS_l_jg)))
{
return true;
}
else
{
return false;
}
#else //! TARGET_AMD64 = TARGET_X86
return false;
#endif //! TARGET_AMD64
}
// Returns true if using this register will require a REX.* prefix.
// Since XMM registers overlap with YMM registers, this routine
// can also be used to know whether a YMM register if the
// instruction in question is AVX.
bool IsExtendedReg(regNumber reg)
{
#ifdef TARGET_AMD64
return ((reg >= REG_R8) && (reg <= REG_R15)) || ((reg >= REG_XMM8) && (reg <= REG_XMM15));
#else
// X86 JIT operates in 32-bit mode and hence extended reg are not available.
return false;
#endif
}
// Returns true if using this register, for the given EA_SIZE(attr), will require a REX.* prefix
bool IsExtendedReg(regNumber reg, emitAttr attr)
{
#ifdef TARGET_AMD64
// Not a register, so doesn't need a prefix
if (reg > REG_XMM15)
{
return false;
}
// Opcode field only has 3 bits for the register, these high registers
// need a 4th bit, that comes from the REX prefix (eiter REX.X, REX.R, or REX.B)
if (IsExtendedReg(reg))
{
return true;
}
if (EA_SIZE(attr) != EA_1BYTE)
{
return false;
}
// There are 12 one byte registers addressible 'below' r8b:
// al, cl, dl, bl, ah, ch, dh, bh, spl, bpl, sil, dil.
// The first 4 are always addressible, the last 8 are divided into 2 sets:
// ah, ch, dh, bh
// -- or --
// spl, bpl, sil, dil
// Both sets are encoded exactly the same, the difference is the presence
// of a REX prefix, even a REX prefix with no other bits set (0x40).
// So in order to get to the second set we need a REX prefix (but no bits).
//
// TODO-AMD64-CQ: if we ever want to start using the first set, we'll need a different way of
// encoding/tracking/encoding registers.
return (reg >= REG_RSP);
#else
// X86 JIT operates in 32-bit mode and hence extended reg are not available.
return false;
#endif
}
// Since XMM registers overlap with YMM registers, this routine
// can also used to know whether a YMM register in case of AVX instructions.
bool IsXMMReg(regNumber reg)
{
#ifdef TARGET_AMD64
return (reg >= REG_XMM0) && (reg <= REG_XMM15);
#else // !TARGET_AMD64
return (reg >= REG_XMM0) && (reg <= REG_XMM7);
#endif // !TARGET_AMD64
}
// Returns bits to be encoded in instruction for the given register.
unsigned RegEncoding(regNumber reg)
{
static_assert((REG_XMM0 & 0x7) == 0, "bad XMMBASE");
return (unsigned)(reg & 0x7);
}
// Utility routines that abstract the logic of adding REX.W, REX.R, REX.X, REX.B and REX prefixes
// SSE2: separate 1-byte prefix gets added before opcode.
// AVX: specific bits within VEX prefix need to be set in bit-inverted form.
emitter::code_t emitter::AddRexWPrefix(instruction ins, code_t code)
{
if (UseVEXEncoding() && IsAVXInstruction(ins))
{
if (TakesVexPrefix(ins))
{
// W-bit is available only in 3-byte VEX prefix that starts with byte C4.
assert(hasVexPrefix(code));
// W-bit is the only bit that is added in non bit-inverted form.
return emitter::code_t(code | 0x00008000000000ULL);
}
}
#ifdef TARGET_AMD64
return emitter::code_t(code | 0x4800000000ULL);
#else
assert(!"UNREACHED");
return code;
#endif
}
#ifdef TARGET_AMD64
emitter::code_t emitter::AddRexRPrefix(instruction ins, code_t code)
{
if (UseVEXEncoding() && IsAVXInstruction(ins))
{
if (TakesVexPrefix(ins))
{
// R-bit is supported by both 2-byte and 3-byte VEX prefix
assert(hasVexPrefix(code));
// R-bit is added in bit-inverted form.
return code & 0xFF7FFFFFFFFFFFULL;
}
}
return code | 0x4400000000ULL;
}
emitter::code_t emitter::AddRexXPrefix(instruction ins, code_t code)
{
if (UseVEXEncoding() && IsAVXInstruction(ins))
{
if (TakesVexPrefix(ins))
{
// X-bit is available only in 3-byte VEX prefix that starts with byte C4.
assert(hasVexPrefix(code));
// X-bit is added in bit-inverted form.
return code & 0xFFBFFFFFFFFFFFULL;
}
}
return code | 0x4200000000ULL;
}
emitter::code_t emitter::AddRexBPrefix(instruction ins, code_t code)
{
if (UseVEXEncoding() && IsAVXInstruction(ins))
{
if (TakesVexPrefix(ins))
{
// B-bit is available only in 3-byte VEX prefix that starts with byte C4.
assert(hasVexPrefix(code));
// B-bit is added in bit-inverted form.
return code & 0xFFDFFFFFFFFFFFULL;
}
}
return code | 0x4100000000ULL;
}
// Adds REX prefix (0x40) without W, R, X or B bits set
emitter::code_t emitter::AddRexPrefix(instruction ins, code_t code)
{
assert(!UseVEXEncoding() || !IsAVXInstruction(ins));
return code | 0x4000000000ULL;
}
#endif // TARGET_AMD64
bool isPrefix(BYTE b)
{
assert(b != 0); // Caller should check this
assert(b != 0x67); // We don't use the address size prefix
assert(b != 0x65); // The GS segment override prefix is emitted separately
assert(b != 0x64); // The FS segment override prefix is emitted separately
assert(b != 0xF0); // The lock prefix is emitted separately
assert(b != 0x2E); // We don't use the CS segment override prefix
assert(b != 0x3E); // Or the DS segment override prefix
assert(b != 0x26); // Or the ES segment override prefix
assert(b != 0x36); // Or the SS segment override prefix
// That just leaves the size prefixes used in SSE opcodes:
// Scalar Double Scalar Single Packed Double
return ((b == 0xF2) || (b == 0xF3) || (b == 0x66));
}
// Outputs VEX prefix (in case of AVX instructions) and REX.R/X/W/B otherwise.
unsigned emitter::emitOutputRexOrVexPrefixIfNeeded(instruction ins, BYTE* dst, code_t& code)
{
if (hasVexPrefix(code))
{
// Only AVX instructions should have a VEX prefix
assert(UseVEXEncoding() && IsAVXInstruction(ins));
code_t vexPrefix = (code >> 32) & 0x00FFFFFF;
code &= 0x00000000FFFFFFFFLL;
WORD leadingBytes = 0;
BYTE check = (code >> 24) & 0xFF;
if (check != 0)
{
// 3-byte opcode: with the bytes ordered as 0x2211RM33 or
// 4-byte opcode: with the bytes ordered as 0x22114433
// check for a prefix in the 11 position
BYTE sizePrefix = (code >> 16) & 0xFF;
if ((sizePrefix != 0) && isPrefix(sizePrefix))
{
// 'pp' bits in byte2 of VEX prefix allows us to encode SIMD size prefixes as two bits
//
// 00 - None (0F - packed float)
// 01 - 66 (66 0F - packed double)
// 10 - F3 (F3 0F - scalar float
// 11 - F2 (F2 0F - scalar double)
switch (sizePrefix)
{
case 0x66:
if (IsBMIInstruction(ins))
{
switch (ins)
{
case INS_rorx:
case INS_pdep:
case INS_mulx:
{
vexPrefix |= 0x03;
break;
}
case INS_pext:
{
vexPrefix |= 0x02;
break;
}
default:
{
vexPrefix |= 0x00;
break;
}
}
}
else
{
vexPrefix |= 0x01;
}
break;
case 0xF3:
vexPrefix |= 0x02;
break;
case 0xF2:
vexPrefix |= 0x03;
break;
default:
assert(!"unrecognized SIMD size prefix");
unreached();
}
// Now the byte in the 22 position must be an escape byte 0F
leadingBytes = check;
assert(leadingBytes == 0x0F);
// Get rid of both sizePrefix and escape byte
code &= 0x0000FFFFLL;
// Check the byte in the 33 position to see if it is 3A or 38.
// In such a case escape bytes must be 0x0F3A or 0x0F38
check = code & 0xFF;
if (check == 0x3A || check == 0x38)
{
leadingBytes = (leadingBytes << 8) | check;
code &= 0x0000FF00LL;
}
}
}
else
{
// 2-byte opcode with the bytes ordered as 0x0011RM22
// the byte in position 11 must be an escape byte.
leadingBytes = (code >> 16) & 0xFF;
assert(leadingBytes == 0x0F || leadingBytes == 0x00);
code &= 0xFFFF;
}
// If there is an escape byte it must be 0x0F or 0x0F3A or 0x0F38
// m-mmmmm bits in byte 1 of VEX prefix allows us to encode these
// implied leading bytes. 0x0F is supported by both the 2-byte and
// 3-byte encoding. While 0x0F3A and 0x0F38 are only supported by
// the 3-byte version.
switch (leadingBytes)
{
case 0x00:
// there is no leading byte
break;
case 0x0F:
vexPrefix |= 0x0100;
break;
case 0x0F38:
vexPrefix |= 0x0200;
break;
case 0x0F3A:
vexPrefix |= 0x0300;
break;
default:
assert(!"encountered unknown leading bytes");
unreached();
}
// At this point
// VEX.2211RM33 got transformed as VEX.0000RM33
// VEX.0011RM22 got transformed as VEX.0000RM22
//
// Now output VEX prefix leaving the 4-byte opcode
// The 2-byte VEX encoding, requires that the X and B-bits are set (these
// bits are inverted from the REX values so set means off), the W-bit is
// not set (this bit is not inverted), and that the m-mmmm bits are 0-0001
// (the 2-byte VEX encoding only supports the 0x0F leading byte). When these
// conditions are met, we can change byte-0 from 0xC4 to 0xC5 and then
// byte-1 is the logical-or of bit 7 from byte-1 and bits 0-6 from byte 2
// from the 3-byte VEX encoding.
//
// Given the above, the check can be reduced to a simple mask and comparison.
// * 0xFFFF7F80 is a mask that ignores any bits whose value we don't care about:
// * R can be set or unset (0x7F ignores bit 7)
// * vvvv can be any value (0x80 ignores bits 3-6)
// * L can be set or unset (0x80 ignores bit 2)
// * pp can be any value (0x80 ignores bits 0-1)
// * 0x00C46100 is a value that signifies the requirements listed above were met:
// * We must be a three-byte VEX opcode (0x00C4)
// * X and B must be set (0x61 validates bits 5-6)
// * m-mmmm must be 0-00001 (0x61 validates bits 0-4)
// * W must be unset (0x00 validates bit 7)
if ((vexPrefix & 0xFFFF7F80) == 0x00C46100)
{
emitOutputByte(dst, 0xC5);
emitOutputByte(dst + 1, ((vexPrefix >> 8) & 0x80) | (vexPrefix & 0x7F));
return 2;
}
emitOutputByte(dst, ((vexPrefix >> 16) & 0xFF));
emitOutputByte(dst + 1, ((vexPrefix >> 8) & 0xFF));
emitOutputByte(dst + 2, vexPrefix & 0xFF);
return 3;
}
#ifdef TARGET_AMD64
if (code > 0x00FFFFFFFFLL)
{
BYTE prefix = (code >> 32) & 0xFF;
noway_assert(prefix >= 0x40 && prefix <= 0x4F);
code &= 0x00000000FFFFFFFFLL;
// TODO-AMD64-Cleanup: when we remove the prefixes (just the SSE opcodes right now)
// we can remove this code as well
// The REX prefix is required to come after all other prefixes.
// Some of our 'opcodes' actually include some prefixes, if that
// is the case, shift them over and place the REX prefix after
// the other prefixes, and emit any prefix that got moved out.
BYTE check = (code >> 24) & 0xFF;
if (check == 0)
{
// 3-byte opcode: with the bytes ordered as 0x00113322
// check for a prefix in the 11 position
check = (code >> 16) & 0xFF;
if (check != 0 && isPrefix(check))
{
// Swap the rex prefix and whatever this prefix is
code = (((DWORD)prefix << 16) | (code & 0x0000FFFFLL));
// and then emit the other prefix
return emitOutputByte(dst, check);
}
}
else
{
// 4-byte opcode with the bytes ordered as 0x22114433
// first check for a prefix in the 11 position
BYTE check2 = (code >> 16) & 0xFF;
if (isPrefix(check2))
{
assert(!isPrefix(check)); // We currently don't use this, so it is untested
if (isPrefix(check))
{
// 3 prefixes were rex = rr, check = c1, check2 = c2 encoded as 0xrrc1c2XXXX
// Change to c2rrc1XXXX, and emit check2 now
code = (((code_t)prefix << 24) | ((code_t)check << 16) | (code & 0x0000FFFFLL));
}
else
{
// 2 prefixes were rex = rr, check2 = c2 encoded as 0xrrXXc2XXXX, (check is part of the opcode)
// Change to c2XXrrXXXX, and emit check2 now
code = (((code_t)check << 24) | ((code_t)prefix << 16) | (code & 0x0000FFFFLL));
}
return emitOutputByte(dst, check2);
}
}
return emitOutputByte(dst, prefix);
}
#endif // TARGET_AMD64
return 0;
}
#ifdef TARGET_AMD64
/*****************************************************************************
* Is the last instruction emitted a call instruction?
*/
bool emitter::emitIsLastInsCall()
{
if ((emitLastIns != nullptr) && (emitLastIns->idIns() == INS_call))
{
return true;
}
return false;
}
/*****************************************************************************
* We're about to create an epilog. If the last instruction we output was a 'call',
* then we need to insert a NOP, to allow for proper exception-handling behavior.
*/
void emitter::emitOutputPreEpilogNOP()
{
if (emitIsLastInsCall())
{
emitIns(INS_nop);
}
}
#endif // TARGET_AMD64
// Size of rex prefix in bytes
unsigned emitter::emitGetRexPrefixSize(instruction ins)
{
// In case of AVX instructions, REX prefixes are part of VEX prefix.
// And hence requires no additional byte to encode REX prefixes.
if (IsAVXInstruction(ins))
{
return 0;
}
// If not AVX, then we would need 1-byte to encode REX prefix.
return 1;
}
// Size of vex prefix in bytes
unsigned emitter::emitGetVexPrefixSize(instruction ins, emitAttr attr)
{
if (IsAVXInstruction(ins))
{
return 3;
}
// If not AVX, then we don't need to encode vex prefix.
return 0;
}