1 //===-- HexagonPeephole.cpp - Hexagon Peephole Optimiztions ---------------===//
2 //
3 //                     The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 // This peephole pass optimizes in the following cases.
9 // 1. Optimizes redundant sign extends for the following case
10 //    Transform the following pattern
11 //    %vreg170<def> = SXTW %vreg166
12 //    ...
13 //    %vreg176<def> = COPY %vreg170:isub_lo
14 //
15 //    Into
16 //    %vreg176<def> = COPY vreg166
17 //
18 //  2. Optimizes redundant negation of predicates.
19 //     %vreg15<def> = CMPGTrr %vreg6, %vreg2
20 //     ...
21 //     %vreg16<def> = NOT_p %vreg15<kill>
22 //     ...
23 //     JMP_c %vreg16<kill>, <BB#1>, %PC<imp-def,dead>
24 //
25 //     Into
26 //     %vreg15<def> = CMPGTrr %vreg6, %vreg2;
27 //     ...
28 //     JMP_cNot %vreg15<kill>, <BB#1>, %PC<imp-def,dead>;
29 //
30 // Note: The peephole pass makes the instrucstions like
31 // %vreg170<def> = SXTW %vreg166 or %vreg16<def> = NOT_p %vreg15<kill>
32 // redundant and relies on some form of dead removal instructions, like
33 // DCE or DIE to actually eliminate them.
34 
35 
36 //===----------------------------------------------------------------------===//
37 
38 #include "Hexagon.h"
39 #include "HexagonTargetMachine.h"
40 #include "llvm/ADT/DenseMap.h"
41 #include "llvm/ADT/Statistic.h"
42 #include "llvm/CodeGen/MachineFunction.h"
43 #include "llvm/CodeGen/MachineFunctionPass.h"
44 #include "llvm/CodeGen/MachineInstrBuilder.h"
45 #include "llvm/CodeGen/MachineRegisterInfo.h"
46 #include "llvm/CodeGen/Passes.h"
47 #include "llvm/IR/Constants.h"
48 #include "llvm/PassSupport.h"
49 #include "llvm/Support/CommandLine.h"
50 #include "llvm/Support/Debug.h"
51 #include "llvm/Support/raw_ostream.h"
52 #include "llvm/Target/TargetInstrInfo.h"
53 #include "llvm/Target/TargetMachine.h"
54 #include "llvm/Target/TargetRegisterInfo.h"
55 #include <algorithm>
56 
57 using namespace llvm;
58 
59 #define DEBUG_TYPE "hexagon-peephole"
60 
61 static cl::opt<bool> DisableHexagonPeephole("disable-hexagon-peephole",
62     cl::Hidden, cl::ZeroOrMore, cl::init(false),
63     cl::desc("Disable Peephole Optimization"));
64 
65 static cl::opt<bool> DisablePNotP("disable-hexagon-pnotp",
66     cl::Hidden, cl::ZeroOrMore, cl::init(false),
67     cl::desc("Disable Optimization of PNotP"));
68 
69 static cl::opt<bool> DisableOptSZExt("disable-hexagon-optszext",
70     cl::Hidden, cl::ZeroOrMore, cl::init(true),
71     cl::desc("Disable Optimization of Sign/Zero Extends"));
72 
73 static cl::opt<bool> DisableOptExtTo64("disable-hexagon-opt-ext-to-64",
74     cl::Hidden, cl::ZeroOrMore, cl::init(true),
75     cl::desc("Disable Optimization of extensions to i64."));
76 
77 namespace llvm {
78   FunctionPass *createHexagonPeephole();
79   void initializeHexagonPeepholePass(PassRegistry&);
80 }
81 
82 namespace {
83   struct HexagonPeephole : public MachineFunctionPass {
84     const HexagonInstrInfo    *QII;
85     const HexagonRegisterInfo *QRI;
86     const MachineRegisterInfo *MRI;
87 
88   public:
89     static char ID;
90     HexagonPeephole() : MachineFunctionPass(ID) {
91       initializeHexagonPeepholePass(*PassRegistry::getPassRegistry());
92     }
93 
94     bool runOnMachineFunction(MachineFunction &MF) override;
95 
96     StringRef getPassName() const override {
97       return "Hexagon optimize redundant zero and size extends";
98     }
99 
100     void getAnalysisUsage(AnalysisUsage &AU) const override {
101       MachineFunctionPass::getAnalysisUsage(AU);
102     }
103 
104   private:
105     void ChangeOpInto(MachineOperand &Dst, MachineOperand &Src);
106   };
107 }
108 
109 char HexagonPeephole::ID = 0;
110 
111 INITIALIZE_PASS(HexagonPeephole, "hexagon-peephole", "Hexagon Peephole",
112                 false, false)
113 
114 bool HexagonPeephole::runOnMachineFunction(MachineFunction &MF) {
115   if (skipFunction(*MF.getFunction()))
116     return false;
117 
118   QII = static_cast<const HexagonInstrInfo *>(MF.getSubtarget().getInstrInfo());
119   QRI = MF.getSubtarget<HexagonSubtarget>().getRegisterInfo();
120   MRI = &MF.getRegInfo();
121 
122   DenseMap<unsigned, unsigned> PeepholeMap;
123   DenseMap<unsigned, std::pair<unsigned, unsigned> > PeepholeDoubleRegsMap;
124 
125   if (DisableHexagonPeephole) return false;
126 
127   // Loop over all of the basic blocks.
128   for (MachineFunction::iterator MBBb = MF.begin(), MBBe = MF.end();
129        MBBb != MBBe; ++MBBb) {
130     MachineBasicBlock *MBB = &*MBBb;
131     PeepholeMap.clear();
132     PeepholeDoubleRegsMap.clear();
133 
134     // Traverse the basic block.
135     for (MachineInstr &MI : *MBB) {
136       // Look for sign extends:
137       // %vreg170<def> = SXTW %vreg166
138       if (!DisableOptSZExt && MI.getOpcode() == Hexagon::A2_sxtw) {
139         assert(MI.getNumOperands() == 2);
140         MachineOperand &Dst = MI.getOperand(0);
141         MachineOperand &Src = MI.getOperand(1);
142         unsigned DstReg = Dst.getReg();
143         unsigned SrcReg = Src.getReg();
144         // Just handle virtual registers.
145         if (TargetRegisterInfo::isVirtualRegister(DstReg) &&
146             TargetRegisterInfo::isVirtualRegister(SrcReg)) {
147           // Map the following:
148           // %vreg170<def> = SXTW %vreg166
149           // PeepholeMap[170] = vreg166
150           PeepholeMap[DstReg] = SrcReg;
151         }
152       }
153 
154       // Look for  %vreg170<def> = COMBINE_ir_V4 (0, %vreg169)
155       // %vreg170:DoublRegs, %vreg169:IntRegs
156       if (!DisableOptExtTo64 && MI.getOpcode() == Hexagon::A4_combineir) {
157         assert(MI.getNumOperands() == 3);
158         MachineOperand &Dst = MI.getOperand(0);
159         MachineOperand &Src1 = MI.getOperand(1);
160         MachineOperand &Src2 = MI.getOperand(2);
161         if (Src1.getImm() != 0)
162           continue;
163         unsigned DstReg = Dst.getReg();
164         unsigned SrcReg = Src2.getReg();
165         PeepholeMap[DstReg] = SrcReg;
166       }
167 
168       // Look for this sequence below
169       // %vregDoubleReg1 = LSRd_ri %vregDoubleReg0, 32
170       // %vregIntReg = COPY %vregDoubleReg1:isub_lo.
171       // and convert into
172       // %vregIntReg = COPY %vregDoubleReg0:isub_hi.
173       if (MI.getOpcode() == Hexagon::S2_lsr_i_p) {
174         assert(MI.getNumOperands() == 3);
175         MachineOperand &Dst = MI.getOperand(0);
176         MachineOperand &Src1 = MI.getOperand(1);
177         MachineOperand &Src2 = MI.getOperand(2);
178         if (Src2.getImm() != 32)
179           continue;
180         unsigned DstReg = Dst.getReg();
181         unsigned SrcReg = Src1.getReg();
182         PeepholeDoubleRegsMap[DstReg] =
183           std::make_pair(*&SrcReg, Hexagon::isub_hi);
184       }
185 
186       // Look for P=NOT(P).
187       if (!DisablePNotP && MI.getOpcode() == Hexagon::C2_not) {
188         assert(MI.getNumOperands() == 2);
189         MachineOperand &Dst = MI.getOperand(0);
190         MachineOperand &Src = MI.getOperand(1);
191         unsigned DstReg = Dst.getReg();
192         unsigned SrcReg = Src.getReg();
193         // Just handle virtual registers.
194         if (TargetRegisterInfo::isVirtualRegister(DstReg) &&
195             TargetRegisterInfo::isVirtualRegister(SrcReg)) {
196           // Map the following:
197           // %vreg170<def> = NOT_xx %vreg166
198           // PeepholeMap[170] = vreg166
199           PeepholeMap[DstReg] = SrcReg;
200         }
201       }
202 
203       // Look for copy:
204       // %vreg176<def> = COPY %vreg170:isub_lo
205       if (!DisableOptSZExt && MI.isCopy()) {
206         assert(MI.getNumOperands() == 2);
207         MachineOperand &Dst = MI.getOperand(0);
208         MachineOperand &Src = MI.getOperand(1);
209 
210         // Make sure we are copying the lower 32 bits.
211         if (Src.getSubReg() != Hexagon::isub_lo)
212           continue;
213 
214         unsigned DstReg = Dst.getReg();
215         unsigned SrcReg = Src.getReg();
216         if (TargetRegisterInfo::isVirtualRegister(DstReg) &&
217             TargetRegisterInfo::isVirtualRegister(SrcReg)) {
218           // Try to find in the map.
219           if (unsigned PeepholeSrc = PeepholeMap.lookup(SrcReg)) {
220             // Change the 1st operand.
221             MI.RemoveOperand(1);
222             MI.addOperand(MachineOperand::CreateReg(PeepholeSrc, false));
223           } else  {
224             DenseMap<unsigned, std::pair<unsigned, unsigned> >::iterator DI =
225               PeepholeDoubleRegsMap.find(SrcReg);
226             if (DI != PeepholeDoubleRegsMap.end()) {
227               std::pair<unsigned,unsigned> PeepholeSrc = DI->second;
228               MI.RemoveOperand(1);
229               MI.addOperand(MachineOperand::CreateReg(
230                   PeepholeSrc.first, false /*isDef*/, false /*isImp*/,
231                   false /*isKill*/, false /*isDead*/, false /*isUndef*/,
232                   false /*isEarlyClobber*/, PeepholeSrc.second));
233             }
234           }
235         }
236       }
237 
238       // Look for Predicated instructions.
239       if (!DisablePNotP) {
240         bool Done = false;
241         if (QII->isPredicated(MI)) {
242           MachineOperand &Op0 = MI.getOperand(0);
243           unsigned Reg0 = Op0.getReg();
244           const TargetRegisterClass *RC0 = MRI->getRegClass(Reg0);
245           if (RC0->getID() == Hexagon::PredRegsRegClassID) {
246             // Handle instructions that have a prediate register in op0
247             // (most cases of predicable instructions).
248             if (TargetRegisterInfo::isVirtualRegister(Reg0)) {
249               // Try to find in the map.
250               if (unsigned PeepholeSrc = PeepholeMap.lookup(Reg0)) {
251                 // Change the 1st operand and, flip the opcode.
252                 MI.getOperand(0).setReg(PeepholeSrc);
253                 MRI->clearKillFlags(PeepholeSrc);
254                 int NewOp = QII->getInvertedPredicatedOpcode(MI.getOpcode());
255                 MI.setDesc(QII->get(NewOp));
256                 Done = true;
257               }
258             }
259           }
260         }
261 
262         if (!Done) {
263           // Handle special instructions.
264           unsigned Op = MI.getOpcode();
265           unsigned NewOp = 0;
266           unsigned PR = 1, S1 = 2, S2 = 3;   // Operand indices.
267 
268           switch (Op) {
269             case Hexagon::C2_mux:
270             case Hexagon::C2_muxii:
271               NewOp = Op;
272               break;
273             case Hexagon::C2_muxri:
274               NewOp = Hexagon::C2_muxir;
275               break;
276             case Hexagon::C2_muxir:
277               NewOp = Hexagon::C2_muxri;
278               break;
279           }
280           if (NewOp) {
281             unsigned PSrc = MI.getOperand(PR).getReg();
282             if (unsigned POrig = PeepholeMap.lookup(PSrc)) {
283               MI.getOperand(PR).setReg(POrig);
284               MRI->clearKillFlags(POrig);
285               MI.setDesc(QII->get(NewOp));
286               // Swap operands S1 and S2.
287               MachineOperand Op1 = MI.getOperand(S1);
288               MachineOperand Op2 = MI.getOperand(S2);
289               ChangeOpInto(MI.getOperand(S1), Op2);
290               ChangeOpInto(MI.getOperand(S2), Op1);
291             }
292           } // if (NewOp)
293         } // if (!Done)
294 
295       } // if (!DisablePNotP)
296 
297     } // Instruction
298   } // Basic Block
299   return true;
300 }
301 
302 void HexagonPeephole::ChangeOpInto(MachineOperand &Dst, MachineOperand &Src) {
303   assert (&Dst != &Src && "Cannot duplicate into itself");
304   switch (Dst.getType()) {
305     case MachineOperand::MO_Register:
306       if (Src.isReg()) {
307         Dst.setReg(Src.getReg());
308         Dst.setSubReg(Src.getSubReg());
309         MRI->clearKillFlags(Src.getReg());
310       } else if (Src.isImm()) {
311         Dst.ChangeToImmediate(Src.getImm());
312       } else {
313         llvm_unreachable("Unexpected src operand type");
314       }
315       break;
316 
317     case MachineOperand::MO_Immediate:
318       if (Src.isImm()) {
319         Dst.setImm(Src.getImm());
320       } else if (Src.isReg()) {
321         Dst.ChangeToRegister(Src.getReg(), Src.isDef(), Src.isImplicit(),
322                              false, Src.isDead(), Src.isUndef(),
323                              Src.isDebug());
324         Dst.setSubReg(Src.getSubReg());
325       } else {
326         llvm_unreachable("Unexpected src operand type");
327       }
328       break;
329 
330     default:
331       llvm_unreachable("Unexpected dst operand type");
332       break;
333   }
334 }
335 
336 FunctionPass *llvm::createHexagonPeephole() {
337   return new HexagonPeephole();
338 }
339