1 //===-- llvm/CodeGen/GlobalISel/Legalizer.cpp -----------------------------===//
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 //
10 /// \file This file implements the LegalizerHelper class to legalize individual
11 /// instructions and the LegalizePass wrapper pass for the primary
12 /// legalization.
13 //
14 //===----------------------------------------------------------------------===//
15 
16 #include "llvm/CodeGen/GlobalISel/Legalizer.h"
17 #include "llvm/ADT/SetVector.h"
18 #include "llvm/CodeGen/GlobalISel/LegalizerCombiner.h"
19 #include "llvm/CodeGen/GlobalISel/LegalizerHelper.h"
20 #include "llvm/CodeGen/GlobalISel/Utils.h"
21 #include "llvm/CodeGen/MachineOptimizationRemarkEmitter.h"
22 #include "llvm/CodeGen/MachineRegisterInfo.h"
23 #include "llvm/CodeGen/TargetPassConfig.h"
24 #include "llvm/Support/Debug.h"
25 #include "llvm/Target/TargetInstrInfo.h"
26 #include "llvm/Target/TargetSubtargetInfo.h"
27 
28 #include <iterator>
29 
30 #define DEBUG_TYPE "legalizer"
31 
32 using namespace llvm;
33 
34 char Legalizer::ID = 0;
35 INITIALIZE_PASS_BEGIN(Legalizer, DEBUG_TYPE,
36                       "Legalize the Machine IR a function's Machine IR", false,
37                       false)
38 INITIALIZE_PASS_DEPENDENCY(TargetPassConfig)
39 INITIALIZE_PASS_END(Legalizer, DEBUG_TYPE,
40                     "Legalize the Machine IR a function's Machine IR", false,
41                     false)
42 
43 Legalizer::Legalizer() : MachineFunctionPass(ID) {
44   initializeLegalizerPass(*PassRegistry::getPassRegistry());
45 }
46 
47 void Legalizer::getAnalysisUsage(AnalysisUsage &AU) const {
48   AU.addRequired<TargetPassConfig>();
49   MachineFunctionPass::getAnalysisUsage(AU);
50 }
51 
52 void Legalizer::init(MachineFunction &MF) {
53 }
54 
55 bool Legalizer::runOnMachineFunction(MachineFunction &MF) {
56   // If the ISel pipeline failed, do not bother running that pass.
57   if (MF.getProperties().hasProperty(
58           MachineFunctionProperties::Property::FailedISel))
59     return false;
60   DEBUG(dbgs() << "Legalize Machine IR for: " << MF.getName() << '\n');
61   init(MF);
62   const TargetPassConfig &TPC = getAnalysis<TargetPassConfig>();
63   MachineOptimizationRemarkEmitter MORE(MF, /*MBFI=*/nullptr);
64   LegalizerHelper Helper(MF);
65 
66   // FIXME: an instruction may need more than one pass before it is legal. For
67   // example on most architectures <3 x i3> is doubly-illegal. It would
68   // typically proceed along a path like: <3 x i3> -> <3 x i8> -> <8 x i8>. We
69   // probably want a worklist of instructions rather than naive iterate until
70   // convergence for performance reasons.
71   bool Changed = false;
72   MachineBasicBlock::iterator NextMI;
73   for (auto &MBB : MF) {
74     for (auto MI = MBB.begin(); MI != MBB.end(); MI = NextMI) {
75       // Get the next Instruction before we try to legalize, because there's a
76       // good chance MI will be deleted.
77       NextMI = std::next(MI);
78 
79       // Only legalize pre-isel generic instructions: others don't have types
80       // and are assumed to be legal.
81       if (!isPreISelGenericOpcode(MI->getOpcode()))
82         continue;
83       unsigned NumNewInsns = 0;
84       using VecType = SetVector<MachineInstr *, SmallVector<MachineInstr *, 8>>;
85       VecType WorkList;
86       VecType CombineList;
87       Helper.MIRBuilder.recordInsertions([&](MachineInstr *MI) {
88         // Only legalize pre-isel generic instructions.
89         // Legalization process could generate Target specific pseudo
90         // instructions with generic types. Don't record them
91         if (isPreISelGenericOpcode(MI->getOpcode())) {
92           ++NumNewInsns;
93           WorkList.insert(MI);
94           CombineList.insert(MI);
95         }
96       });
97       WorkList.insert(&*MI);
98       LegalizerCombiner C(Helper.MIRBuilder, MF.getRegInfo());
99       bool Changed = false;
100       LegalizerHelper::LegalizeResult Res;
101       do {
102         assert(!WorkList.empty() && "Expecting illegal ops");
103         while (!WorkList.empty()) {
104           NumNewInsns = 0;
105           MachineInstr *CurrInst = WorkList.pop_back_val();
106           Res = Helper.legalizeInstrStep(*CurrInst);
107           // Error out if we couldn't legalize this instruction. We may want to
108           // fall back to DAG ISel instead in the future.
109           if (Res == LegalizerHelper::UnableToLegalize) {
110             Helper.MIRBuilder.stopRecordingInsertions();
111             if (Res == LegalizerHelper::UnableToLegalize) {
112               reportGISelFailure(MF, TPC, MORE, "gisel-legalize",
113                                  "unable to legalize instruction", *CurrInst);
114               return false;
115             }
116           }
117           Changed |= Res == LegalizerHelper::Legalized;
118           // If CurrInst was legalized, there's a good chance that it might have
119           // been erased. So remove it from the Combine List.
120           if (Res == LegalizerHelper::Legalized)
121             CombineList.remove(CurrInst);
122 
123 #ifndef NDEBUG
124           if (NumNewInsns)
125             for (unsigned I = WorkList.size() - NumNewInsns,
126                           E = WorkList.size();
127                  I != E; ++I)
128               DEBUG(dbgs() << ".. .. New MI: " << *WorkList[I];);
129 #endif
130         }
131         // Do the combines.
132         while (!CombineList.empty()) {
133           NumNewInsns = 0;
134           MachineInstr *CurrInst = CombineList.pop_back_val();
135           SmallVector<MachineInstr *, 4> DeadInstructions;
136           Changed |= C.tryCombineInstruction(*CurrInst, DeadInstructions);
137           for (auto *DeadMI : DeadInstructions) {
138             DEBUG(dbgs() << ".. Erasing Dead Instruction " << *DeadMI);
139             CombineList.remove(DeadMI);
140             WorkList.remove(DeadMI);
141             DeadMI->eraseFromParent();
142           }
143 #ifndef NDEBUG
144           if (NumNewInsns)
145             for (unsigned I = CombineList.size() - NumNewInsns,
146                           E = CombineList.size();
147                  I != E; ++I)
148               DEBUG(dbgs() << ".. .. Combine New MI: " << *CombineList[I];);
149 #endif
150         }
151       } while (!WorkList.empty());
152 
153       Helper.MIRBuilder.stopRecordingInsertions();
154     }
155   }
156 
157   MachineRegisterInfo &MRI = MF.getRegInfo();
158   MachineIRBuilder MIRBuilder(MF);
159   LegalizerCombiner C(MIRBuilder, MRI);
160   for (auto &MBB : MF) {
161     for (auto MI = MBB.begin(); MI != MBB.end(); MI = NextMI) {
162       // Get the next Instruction before we try to legalize, because there's a
163       // good chance MI will be deleted.
164       // TOOD: Perhaps move this to a combiner pass later?.
165       NextMI = std::next(MI);
166       SmallVector<MachineInstr *, 4> DeadInsts;
167       Changed |= C.tryCombineMerges(*MI, DeadInsts);
168       for (auto *DeadMI : DeadInsts)
169         DeadMI->eraseFromParent();
170     }
171   }
172 
173   return Changed;
174 }
175