LLVM  10.0.0svn
X86EvexToVex.cpp
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1 //===- X86EvexToVex.cpp ---------------------------------------------------===//
2 // Compress EVEX instructions to VEX encoding when possible to reduce code size
3 //
4 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
5 // See https://llvm.org/LICENSE.txt for license information.
6 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 /// \file
11 /// This file defines the pass that goes over all AVX-512 instructions which
12 /// are encoded using the EVEX prefix and if possible replaces them by their
13 /// corresponding VEX encoding which is usually shorter by 2 bytes.
14 /// EVEX instructions may be encoded via the VEX prefix when the AVX-512
15 /// instruction has a corresponding AVX/AVX2 opcode, when vector length
16 /// accessed by instruction is less than 512 bits and when it does not use
17 // the xmm or the mask registers or xmm/ymm registers with indexes higher than 15.
18 /// The pass applies code reduction on the generated code for AVX-512 instrs.
19 //
20 //===----------------------------------------------------------------------===//
21 
24 #include "X86.h"
25 #include "X86InstrInfo.h"
26 #include "X86Subtarget.h"
27 #include "llvm/ADT/StringRef.h"
32 #include "llvm/MC/MCInstrDesc.h"
33 #include "llvm/Pass.h"
34 #include <cassert>
35 #include <cstdint>
36 
37 using namespace llvm;
38 
39 // Including the generated EVEX2VEX tables.
41  uint16_t EvexOpcode;
42  uint16_t VexOpcode;
43 
44  bool operator<(const X86EvexToVexCompressTableEntry &RHS) const {
45  return EvexOpcode < RHS.EvexOpcode;
46  }
47 
49  unsigned Opc) {
50  return TE.EvexOpcode < Opc;
51  }
52 };
53 #include "X86GenEVEX2VEXTables.inc"
54 
55 #define EVEX2VEX_DESC "Compressing EVEX instrs to VEX encoding when possible"
56 #define EVEX2VEX_NAME "x86-evex-to-vex-compress"
57 
58 #define DEBUG_TYPE EVEX2VEX_NAME
59 
60 namespace {
61 
62 class EvexToVexInstPass : public MachineFunctionPass {
63 
64  /// For EVEX instructions that can be encoded using VEX encoding, replace
65  /// them by the VEX encoding in order to reduce size.
66  bool CompressEvexToVexImpl(MachineInstr &MI) const;
67 
68 public:
69  static char ID;
70 
71  EvexToVexInstPass() : MachineFunctionPass(ID) { }
72 
73  StringRef getPassName() const override { return EVEX2VEX_DESC; }
74 
75  /// Loop over all of the basic blocks, replacing EVEX instructions
76  /// by equivalent VEX instructions when possible for reducing code size.
77  bool runOnMachineFunction(MachineFunction &MF) override;
78 
79  // This pass runs after regalloc and doesn't support VReg operands.
80  MachineFunctionProperties getRequiredProperties() const override {
83  }
84 
85 private:
86  /// Machine instruction info used throughout the class.
87  const X86InstrInfo *TII;
88 };
89 
90 } // end anonymous namespace
91 
92 char EvexToVexInstPass::ID = 0;
93 
94 bool EvexToVexInstPass::runOnMachineFunction(MachineFunction &MF) {
95  TII = MF.getSubtarget<X86Subtarget>().getInstrInfo();
96 
98  if (!ST.hasAVX512())
99  return false;
100 
101  bool Changed = false;
102 
103  /// Go over all basic blocks in function and replace
104  /// EVEX encoded instrs by VEX encoding when possible.
105  for (MachineBasicBlock &MBB : MF) {
106 
107  // Traverse the basic block.
108  for (MachineInstr &MI : MBB)
109  Changed |= CompressEvexToVexImpl(MI);
110  }
111 
112  return Changed;
113 }
114 
115 static bool usesExtendedRegister(const MachineInstr &MI) {
116  auto isHiRegIdx = [](unsigned Reg) {
117  // Check for XMM register with indexes between 16 - 31.
118  if (Reg >= X86::XMM16 && Reg <= X86::XMM31)
119  return true;
120 
121  // Check for YMM register with indexes between 16 - 31.
122  if (Reg >= X86::YMM16 && Reg <= X86::YMM31)
123  return true;
124 
125  return false;
126  };
127 
128  // Check that operands are not ZMM regs or
129  // XMM/YMM regs with hi indexes between 16 - 31.
130  for (const MachineOperand &MO : MI.explicit_operands()) {
131  if (!MO.isReg())
132  continue;
133 
134  unsigned Reg = MO.getReg();
135 
136  assert(!(Reg >= X86::ZMM0 && Reg <= X86::ZMM31) &&
137  "ZMM instructions should not be in the EVEX->VEX tables");
138 
139  if (isHiRegIdx(Reg))
140  return true;
141  }
142 
143  return false;
144 }
145 
146 // Do any custom cleanup needed to finalize the conversion.
147 static bool performCustomAdjustments(MachineInstr &MI, unsigned NewOpc) {
148  (void)NewOpc;
149  unsigned Opc = MI.getOpcode();
150  switch (Opc) {
151  case X86::VALIGNDZ128rri:
152  case X86::VALIGNDZ128rmi:
153  case X86::VALIGNQZ128rri:
154  case X86::VALIGNQZ128rmi: {
155  assert((NewOpc == X86::VPALIGNRrri || NewOpc == X86::VPALIGNRrmi) &&
156  "Unexpected new opcode!");
157  unsigned Scale = (Opc == X86::VALIGNQZ128rri ||
158  Opc == X86::VALIGNQZ128rmi) ? 8 : 4;
160  Imm.setImm(Imm.getImm() * Scale);
161  break;
162  }
163  case X86::VSHUFF32X4Z256rmi:
164  case X86::VSHUFF32X4Z256rri:
165  case X86::VSHUFF64X2Z256rmi:
166  case X86::VSHUFF64X2Z256rri:
167  case X86::VSHUFI32X4Z256rmi:
168  case X86::VSHUFI32X4Z256rri:
169  case X86::VSHUFI64X2Z256rmi:
170  case X86::VSHUFI64X2Z256rri: {
171  assert((NewOpc == X86::VPERM2F128rr || NewOpc == X86::VPERM2I128rr ||
172  NewOpc == X86::VPERM2F128rm || NewOpc == X86::VPERM2I128rm) &&
173  "Unexpected new opcode!");
175  int64_t ImmVal = Imm.getImm();
176  // Set bit 5, move bit 1 to bit 4, copy bit 0.
177  Imm.setImm(0x20 | ((ImmVal & 2) << 3) | (ImmVal & 1));
178  break;
179  }
180  case X86::VRNDSCALEPDZ128rri:
181  case X86::VRNDSCALEPDZ128rmi:
182  case X86::VRNDSCALEPSZ128rri:
183  case X86::VRNDSCALEPSZ128rmi:
184  case X86::VRNDSCALEPDZ256rri:
185  case X86::VRNDSCALEPDZ256rmi:
186  case X86::VRNDSCALEPSZ256rri:
187  case X86::VRNDSCALEPSZ256rmi:
188  case X86::VRNDSCALESDZr:
189  case X86::VRNDSCALESDZm:
190  case X86::VRNDSCALESSZr:
191  case X86::VRNDSCALESSZm:
192  case X86::VRNDSCALESDZr_Int:
193  case X86::VRNDSCALESDZm_Int:
194  case X86::VRNDSCALESSZr_Int:
195  case X86::VRNDSCALESSZm_Int:
196  const MachineOperand &Imm = MI.getOperand(MI.getNumExplicitOperands()-1);
197  int64_t ImmVal = Imm.getImm();
198  // Ensure that only bits 3:0 of the immediate are used.
199  if ((ImmVal & 0xf) != ImmVal)
200  return false;
201  break;
202  }
203 
204  return true;
205 }
206 
207 
208 // For EVEX instructions that can be encoded using VEX encoding
209 // replace them by the VEX encoding in order to reduce size.
210 bool EvexToVexInstPass::CompressEvexToVexImpl(MachineInstr &MI) const {
211  // VEX format.
212  // # of bytes: 0,2,3 1 1 0,1 0,1,2,4 0,1
213  // [Prefixes] [VEX] OPCODE ModR/M [SIB] [DISP] [IMM]
214  //
215  // EVEX format.
216  // # of bytes: 4 1 1 1 4 / 1 1
217  // [Prefixes] EVEX Opcode ModR/M [SIB] [Disp32] / [Disp8*N] [Immediate]
218 
219  const MCInstrDesc &Desc = MI.getDesc();
220 
221  // Check for EVEX instructions only.
222  if ((Desc.TSFlags & X86II::EncodingMask) != X86II::EVEX)
223  return false;
224 
225  // Check for EVEX instructions with mask or broadcast as in these cases
226  // the EVEX prefix is needed in order to carry this information
227  // thus preventing the transformation to VEX encoding.
228  if (Desc.TSFlags & (X86II::EVEX_K | X86II::EVEX_B))
229  return false;
230 
231  // Check for EVEX instructions with L2 set. These instructions are 512-bits
232  // and can't be converted to VEX.
233  if (Desc.TSFlags & X86II::EVEX_L2)
234  return false;
235 
236 #ifndef NDEBUG
237  // Make sure the tables are sorted.
238  static std::atomic<bool> TableChecked(false);
239  if (!TableChecked.load(std::memory_order_relaxed)) {
240  assert(std::is_sorted(std::begin(X86EvexToVex128CompressTable),
241  std::end(X86EvexToVex128CompressTable)) &&
242  "X86EvexToVex128CompressTable is not sorted!");
243  assert(std::is_sorted(std::begin(X86EvexToVex256CompressTable),
244  std::end(X86EvexToVex256CompressTable)) &&
245  "X86EvexToVex256CompressTable is not sorted!");
246  TableChecked.store(true, std::memory_order_relaxed);
247  }
248 #endif
249 
250  // Use the VEX.L bit to select the 128 or 256-bit table.
252  (Desc.TSFlags & X86II::VEX_L) ? makeArrayRef(X86EvexToVex256CompressTable)
253  : makeArrayRef(X86EvexToVex128CompressTable);
254 
255  auto I = llvm::lower_bound(Table, MI.getOpcode());
256  if (I == Table.end() || I->EvexOpcode != MI.getOpcode())
257  return false;
258 
259  unsigned NewOpc = I->VexOpcode;
260 
261  if (usesExtendedRegister(MI))
262  return false;
263 
264  if (!performCustomAdjustments(MI, NewOpc))
265  return false;
266 
267  MI.setDesc(TII->get(NewOpc));
269  return true;
270 }
271 
272 INITIALIZE_PASS(EvexToVexInstPass, EVEX2VEX_NAME, EVEX2VEX_DESC, false, false)
273 
275  return new EvexToVexInstPass();
276 }
auto lower_bound(R &&Range, T &&Value) -> decltype(adl_begin(Range))
Provide wrappers to std::lower_bound which take ranges instead of having to pass begin/end explicitly...
Definition: STLExtras.h:1288
const_iterator end(StringRef path)
Get end iterator over path.
Definition: Path.cpp:233
const_iterator begin(StringRef path, Style style=Style::native)
Get begin iterator over path.
Definition: Path.cpp:224
This class represents lattice values for constants.
Definition: AllocatorList.h:23
iterator_range< mop_iterator > explicit_operands()
Definition: MachineInstr.h:467
Describe properties that are true of each instruction in the target description file.
Definition: MCInstrDesc.h:164
unsigned Reg
FunctionPass * createX86EvexToVexInsts()
This pass replaces EVEX encoded of AVX-512 instructiosn by VEX encoding when possible in order to red...
bool operator<(const X86EvexToVexCompressTableEntry &RHS) const
MachineFunctionPass - This class adapts the FunctionPass interface to allow convenient creation of pa...
const HexagonInstrInfo * TII
ArrayRef< T > makeArrayRef(const T &OneElt)
Construct an ArrayRef from a single element.
Definition: ArrayRef.h:450
unsigned getOpcode() const
Returns the opcode of this MachineInstr.
Definition: MachineInstr.h:411
const MCInstrDesc & getDesc() const
Returns the target instruction descriptor of this MachineInstr.
Definition: MachineInstr.h:408
ArrayRef - Represent a constant reference to an array (0 or more elements consecutively in memory)...
Definition: APInt.h:32
const TargetSubtargetInfo & getSubtarget() const
getSubtarget - Return the subtarget for which this machine code is being compiled.
void setImm(int64_t immVal)
FunctionPass class - This class is used to implement most global optimizations.
Definition: Pass.h:284
unsigned getNumExplicitOperands() const
Returns the number of non-implicit operands.
#define INITIALIZE_PASS(passName, arg, name, cfg, analysis)
Definition: PassSupport.h:33
static bool performCustomAdjustments(MachineInstr &MI, unsigned NewOpc)
void setDesc(const MCInstrDesc &tid)
Replace the instruction descriptor (thus opcode) of the current instruction with a new one...
MachineOperand class - Representation of each machine instruction operand.
#define EVEX2VEX_DESC
iterator end() const
Definition: ArrayRef.h:137
int64_t getImm() const
MachineFunctionProperties & set(Property P)
static bool usesExtendedRegister(const MachineInstr &MI)
Representation of each machine instruction.
Definition: MachineInstr.h:64
#define EVEX2VEX_NAME
#define I(x, y, z)
Definition: MD5.cpp:58
assert(ImpDefSCC.getReg()==AMDGPU::SCC &&ImpDefSCC.isDef())
friend bool operator<(const X86EvexToVexCompressTableEntry &TE, unsigned Opc)
bool hasAVX512() const
Definition: X86Subtarget.h:583
IRTranslator LLVM IR MI
StringRef - Represent a constant reference to a string, i.e.
Definition: StringRef.h:48
void setAsmPrinterFlag(uint8_t Flag)
Set a flag for the AsmPrinter.
Definition: MachineInstr.h:282
const MachineOperand & getOperand(unsigned i) const
Definition: MachineInstr.h:416
Properties which a MachineFunction may have at a given point in time.