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 }
45 
46 void LegalizerInfo::computeTables() {
47   for (unsigned Opcode = 0; Opcode <= LastOp - FirstOp; ++Opcode) {
48     for (unsigned Idx = 0; Idx != Actions[Opcode].size(); ++Idx) {
49       for (auto &Action : Actions[Opcode][Idx]) {
50         LLT Ty = Action.first;
51         if (!Ty.isVector())
52           continue;
53 
54         auto &Entry = MaxLegalVectorElts[std::make_pair(Opcode + FirstOp,
55                                                         Ty.getElementType())];
56         Entry = std::max(Entry, Ty.getNumElements());
57       }
58     }
59   }
60 
61   TablesInitialized = true;
62 }
63 
64 // FIXME: inefficient implementation for now. Without ComputeValueVTs we're
65 // probably going to need specialized lookup structures for various types before
66 // we have any hope of doing well with something like <13 x i3>. Even the common
67 // cases should do better than what we have now.
68 std::pair<LegalizerInfo::LegalizeAction, LLT>
69 LegalizerInfo::getAction(const InstrAspect &Aspect) const {
70   assert(TablesInitialized && "backend forgot to call computeTables");
71   // These *have* to be implemented for now, they're the fundamental basis of
72   // how everything else is transformed.
73 
74   // FIXME: the long-term plan calls for expansion in terms of load/store (if
75   // they're not legal).
76   if (Aspect.Opcode == TargetOpcode::G_SEQUENCE ||
77       Aspect.Opcode == TargetOpcode::G_EXTRACT)
78     return std::make_pair(Legal, Aspect.Type);
79 
80   LegalizeAction Action = findInActions(Aspect);
81   if (Action != NotFound)
82     return findLegalAction(Aspect, Action);
83 
84   unsigned Opcode = Aspect.Opcode;
85   LLT Ty = Aspect.Type;
86   if (!Ty.isVector()) {
87     auto DefaultAction = DefaultActions.find(Aspect.Opcode);
88     if (DefaultAction != DefaultActions.end() && DefaultAction->second == Legal)
89       return std::make_pair(Legal, Ty);
90 
91     assert(DefaultAction->second == NarrowScalar && "unexpected default");
92     return findLegalAction(Aspect, NarrowScalar);
93   }
94 
95   LLT EltTy = Ty.getElementType();
96   int NumElts = Ty.getNumElements();
97 
98   auto ScalarAction = ScalarInVectorActions.find(std::make_pair(Opcode, EltTy));
99   if (ScalarAction != ScalarInVectorActions.end() &&
100       ScalarAction->second != Legal)
101     return findLegalAction(Aspect, ScalarAction->second);
102 
103   // The element type is legal in principle, but the number of elements is
104   // wrong.
105   auto MaxLegalElts = MaxLegalVectorElts.lookup(std::make_pair(Opcode, EltTy));
106   if (MaxLegalElts > NumElts)
107     return findLegalAction(Aspect, MoreElements);
108 
109   if (MaxLegalElts == 0) {
110     // Scalarize if there's no legal vector type, which is just a special case
111     // of FewerElements.
112     return std::make_pair(FewerElements, EltTy);
113   }
114 
115   return findLegalAction(Aspect, FewerElements);
116 }
117 
118 std::tuple<LegalizerInfo::LegalizeAction, unsigned, LLT>
119 LegalizerInfo::getAction(const MachineInstr &MI,
120                          const MachineRegisterInfo &MRI) const {
121   SmallBitVector SeenTypes(8);
122   const MCOperandInfo *OpInfo = MI.getDesc().OpInfo;
123   for (unsigned i = 0; i < MI.getDesc().getNumOperands(); ++i) {
124     if (!OpInfo[i].isGenericType())
125       continue;
126 
127     // We don't want to repeatedly check the same operand index, that
128     // could get expensive.
129     unsigned TypeIdx = OpInfo[i].getGenericTypeIndex();
130     if (SeenTypes[TypeIdx])
131       continue;
132 
133     SeenTypes.set(TypeIdx);
134 
135     LLT Ty = MRI.getType(MI.getOperand(i).getReg());
136     auto Action = getAction({MI.getOpcode(), TypeIdx, Ty});
137     if (Action.first != Legal)
138       return std::make_tuple(Action.first, TypeIdx, Action.second);
139   }
140   return std::make_tuple(Legal, 0, LLT{});
141 }
142 
143 bool LegalizerInfo::isLegal(const MachineInstr &MI,
144                             const MachineRegisterInfo &MRI) const {
145   return std::get<0>(getAction(MI, MRI)) == Legal;
146 }
147 
148 LLT LegalizerInfo::findLegalType(const InstrAspect &Aspect,
149                                  LegalizeAction Action) const {
150   switch(Action) {
151   default:
152     llvm_unreachable("Cannot find legal type");
153   case Legal:
154   case Lower:
155   case Libcall:
156     return Aspect.Type;
157   case NarrowScalar: {
158     return findLegalType(Aspect,
159                          [&](LLT Ty) -> LLT { return Ty.halfScalarSize(); });
160   }
161   case WidenScalar: {
162     return findLegalType(Aspect, [&](LLT Ty) -> LLT {
163       return Ty.getSizeInBits() < 8 ? LLT::scalar(8) : Ty.doubleScalarSize();
164     });
165   }
166   case FewerElements: {
167     return findLegalType(Aspect,
168                          [&](LLT Ty) -> LLT { return Ty.halfElements(); });
169   }
170   case MoreElements: {
171     return findLegalType(Aspect,
172                          [&](LLT Ty) -> LLT { return Ty.doubleElements(); });
173   }
174   }
175 }
176