1 //===-- llvm/CodeGen/GlobalISel/CSEMIRBuilder.cpp - MIBuilder--*- C++ -*-==//
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 //===----------------------------------------------------------------------===//
9 /// \file
10 /// This file implements the CSEMIRBuilder class which CSEs as it builds
11 /// instructions.
12 //===----------------------------------------------------------------------===//
13 //
14 
15 #include "llvm/CodeGen/GlobalISel/CSEMIRBuilder.h"
16 #include "llvm/CodeGen/GlobalISel/GISelChangeObserver.h"
17 
18 using namespace llvm;
19 
20 bool CSEMIRBuilder::dominates(MachineBasicBlock::const_iterator A,
21                               MachineBasicBlock::const_iterator B) const {
22   auto MBBEnd = getMBB().end();
23   if (B == MBBEnd)
24     return true;
25   assert(A->getParent() == B->getParent() &&
26          "Iterators should be in same block");
27   const MachineBasicBlock *BBA = A->getParent();
28   MachineBasicBlock::const_iterator I = BBA->begin();
29   for (; &*I != A && &*I != B; ++I)
30     ;
31   return &*I == A;
32 }
33 
34 MachineInstrBuilder
35 CSEMIRBuilder::getDominatingInstrForID(FoldingSetNodeID &ID,
36                                        void *&NodeInsertPos) {
37   GISelCSEInfo *CSEInfo = getCSEInfo();
38   assert(CSEInfo && "Can't get here without setting CSEInfo");
39   MachineBasicBlock *CurMBB = &getMBB();
40   MachineInstr *MI =
41       CSEInfo->getMachineInstrIfExists(ID, CurMBB, NodeInsertPos);
42   if (MI) {
43     auto CurrPos = getInsertPt();
44     if (!dominates(MI, CurrPos))
45       CurMBB->splice(CurrPos, CurMBB, MI);
46     return MachineInstrBuilder(getMF(), MI);
47   }
48   return MachineInstrBuilder();
49 }
50 
51 bool CSEMIRBuilder::canPerformCSEForOpc(unsigned Opc) const {
52   const GISelCSEInfo *CSEInfo = getCSEInfo();
53   if (!CSEInfo || !CSEInfo->shouldCSE(Opc))
54     return false;
55   return true;
56 }
57 
58 void CSEMIRBuilder::profileDstOp(const DstOp &Op,
59                                  GISelInstProfileBuilder &B) const {
60   switch (Op.getDstOpKind()) {
61   case DstOp::DstType::Ty_RC:
62     B.addNodeIDRegType(Op.getRegClass());
63     break;
64   default:
65     B.addNodeIDRegType(Op.getLLTTy(*getMRI()));
66     break;
67   }
68 }
69 
70 void CSEMIRBuilder::profileSrcOp(const SrcOp &Op,
71                                  GISelInstProfileBuilder &B) const {
72   switch (Op.getSrcOpKind()) {
73   case SrcOp::SrcType::Ty_Predicate:
74     B.addNodeIDImmediate(static_cast<int64_t>(Op.getPredicate()));
75     break;
76   default:
77     B.addNodeIDRegType(Op.getReg());
78     break;
79   }
80 }
81 
82 void CSEMIRBuilder::profileMBBOpcode(GISelInstProfileBuilder &B,
83                                      unsigned Opc) const {
84   // First add the MBB (Local CSE).
85   B.addNodeIDMBB(&getMBB());
86   // Then add the opcode.
87   B.addNodeIDOpcode(Opc);
88 }
89 
90 void CSEMIRBuilder::profileEverything(unsigned Opc, ArrayRef<DstOp> DstOps,
91                                       ArrayRef<SrcOp> SrcOps,
92                                       Optional<unsigned> Flags,
93                                       GISelInstProfileBuilder &B) const {
94 
95   profileMBBOpcode(B, Opc);
96   // Then add the DstOps.
97   profileDstOps(DstOps, B);
98   // Then add the SrcOps.
99   profileSrcOps(SrcOps, B);
100   // Add Flags if passed in.
101   if (Flags)
102     B.addNodeIDFlag(*Flags);
103 }
104 
105 MachineInstrBuilder CSEMIRBuilder::memoizeMI(MachineInstrBuilder MIB,
106                                              void *NodeInsertPos) {
107   assert(canPerformCSEForOpc(MIB->getOpcode()) &&
108          "Attempting to CSE illegal op");
109   MachineInstr *MIBInstr = MIB;
110   getCSEInfo()->insertInstr(MIBInstr, NodeInsertPos);
111   return MIB;
112 }
113 
114 bool CSEMIRBuilder::checkCopyToDefsPossible(ArrayRef<DstOp> DstOps) {
115   if (DstOps.size() == 1)
116     return true; // always possible to emit copy to just 1 vreg.
117 
118   return std::all_of(DstOps.begin(), DstOps.end(), [](const DstOp &Op) {
119     DstOp::DstType DT = Op.getDstOpKind();
120     return DT == DstOp::DstType::Ty_LLT || DT == DstOp::DstType::Ty_RC;
121   });
122 }
123 
124 MachineInstrBuilder
125 CSEMIRBuilder::generateCopiesIfRequired(ArrayRef<DstOp> DstOps,
126                                         MachineInstrBuilder &MIB) {
127   assert(checkCopyToDefsPossible(DstOps) &&
128          "Impossible return a single MIB with copies to multiple defs");
129   if (DstOps.size() == 1) {
130     const DstOp &Op = DstOps[0];
131     if (Op.getDstOpKind() == DstOp::DstType::Ty_Reg)
132       return buildCopy(Op.getReg(), MIB->getOperand(0).getReg());
133   }
134   return MIB;
135 }
136 
137 MachineInstrBuilder CSEMIRBuilder::buildInstr(unsigned Opc,
138                                               ArrayRef<DstOp> DstOps,
139                                               ArrayRef<SrcOp> SrcOps,
140                                               Optional<unsigned> Flag) {
141   switch (Opc) {
142   default:
143     break;
144   case TargetOpcode::G_ADD:
145   case TargetOpcode::G_AND:
146   case TargetOpcode::G_ASHR:
147   case TargetOpcode::G_LSHR:
148   case TargetOpcode::G_MUL:
149   case TargetOpcode::G_OR:
150   case TargetOpcode::G_SHL:
151   case TargetOpcode::G_SUB:
152   case TargetOpcode::G_XOR:
153   case TargetOpcode::G_UDIV:
154   case TargetOpcode::G_SDIV:
155   case TargetOpcode::G_UREM:
156   case TargetOpcode::G_SREM: {
157     // Try to constant fold these.
158     assert(SrcOps.size() == 2 && "Invalid sources");
159     assert(DstOps.size() == 1 && "Invalid dsts");
160     if (Optional<APInt> Cst = ConstantFoldBinOp(Opc, SrcOps[0].getReg(),
161                                                 SrcOps[1].getReg(), *getMRI()))
162       return buildConstant(DstOps[0], Cst->getSExtValue());
163     break;
164   }
165   }
166   bool CanCopy = checkCopyToDefsPossible(DstOps);
167   if (!canPerformCSEForOpc(Opc))
168     return MachineIRBuilder::buildInstr(Opc, DstOps, SrcOps, Flag);
169   // If we can CSE this instruction, but involves generating copies to multiple
170   // regs, give up. This frequently happens to UNMERGEs.
171   if (!CanCopy) {
172     auto MIB = MachineIRBuilder::buildInstr(Opc, DstOps, SrcOps, Flag);
173     // CSEInfo would have tracked this instruction. Remove it from the temporary
174     // insts.
175     getCSEInfo()->handleRemoveInst(&*MIB);
176     return MIB;
177   }
178   FoldingSetNodeID ID;
179   GISelInstProfileBuilder ProfBuilder(ID, *getMRI());
180   void *InsertPos = nullptr;
181   profileEverything(Opc, DstOps, SrcOps, Flag, ProfBuilder);
182   MachineInstrBuilder MIB = getDominatingInstrForID(ID, InsertPos);
183   if (MIB) {
184     // Handle generating copies here.
185     return generateCopiesIfRequired(DstOps, MIB);
186   }
187   // This instruction does not exist in the CSEInfo. Build it and CSE it.
188   MachineInstrBuilder NewMIB =
189       MachineIRBuilder::buildInstr(Opc, DstOps, SrcOps, Flag);
190   return memoizeMI(NewMIB, InsertPos);
191 }
192 
193 MachineInstrBuilder CSEMIRBuilder::buildConstant(const DstOp &Res,
194                                                  const ConstantInt &Val) {
195   constexpr unsigned Opc = TargetOpcode::G_CONSTANT;
196   if (!canPerformCSEForOpc(Opc))
197     return MachineIRBuilder::buildConstant(Res, Val);
198   FoldingSetNodeID ID;
199   GISelInstProfileBuilder ProfBuilder(ID, *getMRI());
200   void *InsertPos = nullptr;
201   profileMBBOpcode(ProfBuilder, Opc);
202   profileDstOp(Res, ProfBuilder);
203   ProfBuilder.addNodeIDMachineOperand(MachineOperand::CreateCImm(&Val));
204   MachineInstrBuilder MIB = getDominatingInstrForID(ID, InsertPos);
205   if (MIB) {
206     // Handle generating copies here.
207     return generateCopiesIfRequired({Res}, MIB);
208   }
209   MachineInstrBuilder NewMIB = MachineIRBuilder::buildConstant(Res, Val);
210   return memoizeMI(NewMIB, InsertPos);
211 }
212 
213 MachineInstrBuilder CSEMIRBuilder::buildFConstant(const DstOp &Res,
214                                                   const ConstantFP &Val) {
215   constexpr unsigned Opc = TargetOpcode::G_FCONSTANT;
216   if (!canPerformCSEForOpc(Opc))
217     return MachineIRBuilder::buildFConstant(Res, Val);
218   FoldingSetNodeID ID;
219   GISelInstProfileBuilder ProfBuilder(ID, *getMRI());
220   void *InsertPos = nullptr;
221   profileMBBOpcode(ProfBuilder, Opc);
222   profileDstOp(Res, ProfBuilder);
223   ProfBuilder.addNodeIDMachineOperand(MachineOperand::CreateFPImm(&Val));
224   MachineInstrBuilder MIB = getDominatingInstrForID(ID, InsertPos);
225   if (MIB) {
226     // Handle generating copies here.
227     return generateCopiesIfRequired({Res}, MIB);
228   }
229   MachineInstrBuilder NewMIB = MachineIRBuilder::buildFConstant(Res, Val);
230   return memoizeMI(NewMIB, InsertPos);
231 }
232