1 //===---- lib/CodeGen/GlobalISel/LegalizerInfo.cpp - Legalizer -------==//
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 // Implement an interface to specify and query how an illegal operation on a
11 // given type should be expanded.
12 //
13 // Issues to be resolved:
14 //   + Make it fast.
15 //   + Support weird types like i3, <7 x i3>, ...
16 //   + Operations with more than one type (ICMP, CMPXCHG, intrinsics, ...)
17 //
18 //===----------------------------------------------------------------------===//
19 
20 #include "llvm/CodeGen/GlobalISel/LegalizerInfo.h"
21 
22 #include "llvm/ADT/SmallBitVector.h"
23 #include "llvm/CodeGen/MachineInstr.h"
24 #include "llvm/CodeGen/MachineRegisterInfo.h"
25 #include "llvm/CodeGen/ValueTypes.h"
26 #include "llvm/IR/Type.h"
27 #include "llvm/Target/TargetOpcodes.h"
28 using namespace llvm;
29 
30 LegalizerInfo::LegalizerInfo() : TablesInitialized(false) {
31   // FIXME: these two can be legalized to the fundamental load/store Jakob
32   // proposed. Once loads & stores are supported.
33   DefaultActions[TargetOpcode::G_ANYEXT] = Legal;
34   DefaultActions[TargetOpcode::G_TRUNC] = Legal;
35 
36   DefaultActions[TargetOpcode::G_INTRINSIC] = Legal;
37   DefaultActions[TargetOpcode::G_INTRINSIC_W_SIDE_EFFECTS] = Legal;
38 
39   DefaultActions[TargetOpcode::G_ADD] = NarrowScalar;
40   DefaultActions[TargetOpcode::G_LOAD] = NarrowScalar;
41   DefaultActions[TargetOpcode::G_STORE] = NarrowScalar;
42 
43   DefaultActions[TargetOpcode::G_BRCOND] = WidenScalar;
44   DefaultActions[TargetOpcode::G_INSERT] = NarrowScalar;
45   DefaultActions[TargetOpcode::G_FNEG] = Lower;
46 }
47 
48 void LegalizerInfo::computeTables() {
49   for (unsigned Opcode = 0; Opcode <= LastOp - FirstOp; ++Opcode) {
50     for (unsigned Idx = 0; Idx != Actions[Opcode].size(); ++Idx) {
51       for (auto &Action : Actions[Opcode][Idx]) {
52         LLT Ty = Action.first;
53         if (!Ty.isVector())
54           continue;
55 
56         auto &Entry = MaxLegalVectorElts[std::make_pair(Opcode + FirstOp,
57                                                         Ty.getElementType())];
58         Entry = std::max(Entry, Ty.getNumElements());
59       }
60     }
61   }
62 
63   TablesInitialized = true;
64 }
65 
66 // FIXME: inefficient implementation for now. Without ComputeValueVTs we're
67 // probably going to need specialized lookup structures for various types before
68 // we have any hope of doing well with something like <13 x i3>. Even the common
69 // cases should do better than what we have now.
70 std::pair<LegalizerInfo::LegalizeAction, LLT>
71 LegalizerInfo::getAction(const InstrAspect &Aspect) const {
72   assert(TablesInitialized && "backend forgot to call computeTables");
73   // These *have* to be implemented for now, they're the fundamental basis of
74   // how everything else is transformed.
75 
76   // FIXME: the long-term plan calls for expansion in terms of load/store (if
77   // they're not legal).
78   if (Aspect.Opcode == TargetOpcode::G_EXTRACT ||
79       Aspect.Opcode == TargetOpcode::G_MERGE_VALUES ||
80       Aspect.Opcode == TargetOpcode::G_UNMERGE_VALUES)
81     return std::make_pair(Legal, Aspect.Type);
82 
83   LLT Ty = Aspect.Type;
84   LegalizeAction Action = findInActions(Aspect);
85   // LegalizerHelper is not able to handle non-power-of-2 types right now, so do
86   // not try to legalize them unless they are marked as Legal or Custom.
87   // FIXME: This is a temporary hack until the general non-power-of-2
88   // legalization works.
89   if (!isPowerOf2_64(Ty.getSizeInBits()) &&
90       !(Action == Legal || Action == Custom))
91     return std::make_pair(Unsupported, LLT());
92 
93   if (Action != NotFound)
94     return findLegalAction(Aspect, Action);
95 
96   unsigned Opcode = Aspect.Opcode;
97   if (!Ty.isVector()) {
98     auto DefaultAction = DefaultActions.find(Aspect.Opcode);
99     if (DefaultAction != DefaultActions.end() && DefaultAction->second == Legal)
100       return std::make_pair(Legal, Ty);
101 
102     if (DefaultAction != DefaultActions.end() && DefaultAction->second == Lower)
103       return std::make_pair(Lower, Ty);
104 
105     if (DefaultAction == DefaultActions.end() ||
106         DefaultAction->second != NarrowScalar)
107       return std::make_pair(Unsupported, LLT());
108     return findLegalAction(Aspect, NarrowScalar);
109   }
110 
111   LLT EltTy = Ty.getElementType();
112   int NumElts = Ty.getNumElements();
113 
114   auto ScalarAction = ScalarInVectorActions.find(std::make_pair(Opcode, EltTy));
115   if (ScalarAction != ScalarInVectorActions.end() &&
116       ScalarAction->second != Legal)
117     return findLegalAction(Aspect, ScalarAction->second);
118 
119   // The element type is legal in principle, but the number of elements is
120   // wrong.
121   auto MaxLegalElts = MaxLegalVectorElts.lookup(std::make_pair(Opcode, EltTy));
122   if (MaxLegalElts > NumElts)
123     return findLegalAction(Aspect, MoreElements);
124 
125   if (MaxLegalElts == 0) {
126     // Scalarize if there's no legal vector type, which is just a special case
127     // of FewerElements.
128     return std::make_pair(FewerElements, EltTy);
129   }
130 
131   return findLegalAction(Aspect, FewerElements);
132 }
133 
134 std::tuple<LegalizerInfo::LegalizeAction, unsigned, LLT>
135 LegalizerInfo::getAction(const MachineInstr &MI,
136                          const MachineRegisterInfo &MRI) const {
137   SmallBitVector SeenTypes(8);
138   const MCOperandInfo *OpInfo = MI.getDesc().OpInfo;
139   for (unsigned i = 0; i < MI.getDesc().getNumOperands(); ++i) {
140     if (!OpInfo[i].isGenericType())
141       continue;
142 
143     // We don't want to repeatedly check the same operand index, that
144     // could get expensive.
145     unsigned TypeIdx = OpInfo[i].getGenericTypeIndex();
146     if (SeenTypes[TypeIdx])
147       continue;
148 
149     SeenTypes.set(TypeIdx);
150 
151     LLT Ty = MRI.getType(MI.getOperand(i).getReg());
152     auto Action = getAction({MI.getOpcode(), TypeIdx, Ty});
153     if (Action.first != Legal)
154       return std::make_tuple(Action.first, TypeIdx, Action.second);
155   }
156   return std::make_tuple(Legal, 0, LLT{});
157 }
158 
159 bool LegalizerInfo::isLegal(const MachineInstr &MI,
160                             const MachineRegisterInfo &MRI) const {
161   return std::get<0>(getAction(MI, MRI)) == Legal;
162 }
163 
164 Optional<LLT> LegalizerInfo::findLegalType(const InstrAspect &Aspect,
165                                  LegalizeAction Action) const {
166   switch(Action) {
167   default:
168     llvm_unreachable("Cannot find legal type");
169   case Legal:
170   case Lower:
171   case Libcall:
172   case Custom:
173     return Aspect.Type;
174   case NarrowScalar: {
175     return findLegalType(Aspect,
176                          [](LLT Ty) -> LLT { return Ty.halfScalarSize(); });
177   }
178   case WidenScalar: {
179     return findLegalType(Aspect, [](LLT Ty) -> LLT {
180       return Ty.getSizeInBits() < 8 ? LLT::scalar(8) : Ty.doubleScalarSize();
181     });
182   }
183   case FewerElements: {
184     return findLegalType(Aspect,
185                          [](LLT Ty) -> LLT { return Ty.halfElements(); });
186   }
187   case MoreElements: {
188     return findLegalType(Aspect,
189                          [](LLT Ty) -> LLT { return Ty.doubleElements(); });
190   }
191   }
192 }
193 
194 bool LegalizerInfo::legalizeCustom(MachineInstr &MI,
195                                    MachineRegisterInfo &MRI,
196                                    MachineIRBuilder &MIRBuilder) const {
197   return false;
198 }
199