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   // Nothing is going to go well with types that aren't a power of 2 yet, so
75   // don't even try because we might make things worse.
76   if (!isPowerOf2_64(Aspect.Type.getSizeInBits()))
77       return std::make_pair(Unsupported, LLT());
78 
79   // FIXME: the long-term plan calls for expansion in terms of load/store (if
80   // they're not legal).
81   if (Aspect.Opcode == TargetOpcode::G_SEQUENCE ||
82       Aspect.Opcode == TargetOpcode::G_EXTRACT)
83     return std::make_pair(Legal, Aspect.Type);
84 
85   LegalizeAction Action = findInActions(Aspect);
86   if (Action != NotFound)
87     return findLegalAction(Aspect, Action);
88 
89   unsigned Opcode = Aspect.Opcode;
90   LLT Ty = Aspect.Type;
91   if (!Ty.isVector()) {
92     auto DefaultAction = DefaultActions.find(Aspect.Opcode);
93     if (DefaultAction != DefaultActions.end() && DefaultAction->second == Legal)
94       return std::make_pair(Legal, Ty);
95 
96     if (DefaultAction == DefaultActions.end() ||
97         DefaultAction->second != NarrowScalar)
98       return std::make_pair(Unsupported, LLT());
99     return findLegalAction(Aspect, NarrowScalar);
100   }
101 
102   LLT EltTy = Ty.getElementType();
103   int NumElts = Ty.getNumElements();
104 
105   auto ScalarAction = ScalarInVectorActions.find(std::make_pair(Opcode, EltTy));
106   if (ScalarAction != ScalarInVectorActions.end() &&
107       ScalarAction->second != Legal)
108     return findLegalAction(Aspect, ScalarAction->second);
109 
110   // The element type is legal in principle, but the number of elements is
111   // wrong.
112   auto MaxLegalElts = MaxLegalVectorElts.lookup(std::make_pair(Opcode, EltTy));
113   if (MaxLegalElts > NumElts)
114     return findLegalAction(Aspect, MoreElements);
115 
116   if (MaxLegalElts == 0) {
117     // Scalarize if there's no legal vector type, which is just a special case
118     // of FewerElements.
119     return std::make_pair(FewerElements, EltTy);
120   }
121 
122   return findLegalAction(Aspect, FewerElements);
123 }
124 
125 std::tuple<LegalizerInfo::LegalizeAction, unsigned, LLT>
126 LegalizerInfo::getAction(const MachineInstr &MI,
127                          const MachineRegisterInfo &MRI) const {
128   SmallBitVector SeenTypes(8);
129   const MCOperandInfo *OpInfo = MI.getDesc().OpInfo;
130   for (unsigned i = 0; i < MI.getDesc().getNumOperands(); ++i) {
131     if (!OpInfo[i].isGenericType())
132       continue;
133 
134     // We don't want to repeatedly check the same operand index, that
135     // could get expensive.
136     unsigned TypeIdx = OpInfo[i].getGenericTypeIndex();
137     if (SeenTypes[TypeIdx])
138       continue;
139 
140     SeenTypes.set(TypeIdx);
141 
142     LLT Ty = MRI.getType(MI.getOperand(i).getReg());
143     auto Action = getAction({MI.getOpcode(), TypeIdx, Ty});
144     if (Action.first != Legal)
145       return std::make_tuple(Action.first, TypeIdx, Action.second);
146   }
147   return std::make_tuple(Legal, 0, LLT{});
148 }
149 
150 bool LegalizerInfo::isLegal(const MachineInstr &MI,
151                             const MachineRegisterInfo &MRI) const {
152   return std::get<0>(getAction(MI, MRI)) == Legal;
153 }
154 
155 LLT LegalizerInfo::findLegalType(const InstrAspect &Aspect,
156                                  LegalizeAction Action) const {
157   switch(Action) {
158   default:
159     llvm_unreachable("Cannot find legal type");
160   case Legal:
161   case Lower:
162   case Libcall:
163     return Aspect.Type;
164   case NarrowScalar: {
165     return findLegalType(Aspect,
166                          [&](LLT Ty) -> LLT { return Ty.halfScalarSize(); });
167   }
168   case WidenScalar: {
169     return findLegalType(Aspect, [&](LLT Ty) -> LLT {
170       return Ty.getSizeInBits() < 8 ? LLT::scalar(8) : Ty.doubleScalarSize();
171     });
172   }
173   case FewerElements: {
174     return findLegalType(Aspect,
175                          [&](LLT Ty) -> LLT { return Ty.halfElements(); });
176   }
177   case MoreElements: {
178     return findLegalType(Aspect,
179                          [&](LLT Ty) -> LLT { return Ty.doubleElements(); });
180   }
181   }
182 }
183