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   // Nothing is going to go well with types that aren't a power of 2 yet, so
77   // don't even try because we might make things worse.
78   if (!isPowerOf2_64(Aspect.Type.getSizeInBits()))
79       return std::make_pair(Unsupported, LLT());
80 
81   // FIXME: the long-term plan calls for expansion in terms of load/store (if
82   // they're not legal).
83   if (Aspect.Opcode == TargetOpcode::G_SEQUENCE ||
84       Aspect.Opcode == TargetOpcode::G_EXTRACT ||
85       Aspect.Opcode == TargetOpcode::G_MERGE_VALUES ||
86       Aspect.Opcode == TargetOpcode::G_UNMERGE_VALUES)
87     return std::make_pair(Legal, Aspect.Type);
88 
89   LegalizeAction Action = findInActions(Aspect);
90   if (Action != NotFound)
91     return findLegalAction(Aspect, Action);
92 
93   unsigned Opcode = Aspect.Opcode;
94   LLT Ty = Aspect.Type;
95   if (!Ty.isVector()) {
96     auto DefaultAction = DefaultActions.find(Aspect.Opcode);
97     if (DefaultAction != DefaultActions.end() && DefaultAction->second == Legal)
98       return std::make_pair(Legal, Ty);
99 
100     if (DefaultAction != DefaultActions.end() && DefaultAction->second == Lower)
101       return std::make_pair(Lower, Ty);
102 
103     if (DefaultAction == DefaultActions.end() ||
104         DefaultAction->second != NarrowScalar)
105       return std::make_pair(Unsupported, LLT());
106     return findLegalAction(Aspect, NarrowScalar);
107   }
108 
109   LLT EltTy = Ty.getElementType();
110   int NumElts = Ty.getNumElements();
111 
112   auto ScalarAction = ScalarInVectorActions.find(std::make_pair(Opcode, EltTy));
113   if (ScalarAction != ScalarInVectorActions.end() &&
114       ScalarAction->second != Legal)
115     return findLegalAction(Aspect, ScalarAction->second);
116 
117   // The element type is legal in principle, but the number of elements is
118   // wrong.
119   auto MaxLegalElts = MaxLegalVectorElts.lookup(std::make_pair(Opcode, EltTy));
120   if (MaxLegalElts > NumElts)
121     return findLegalAction(Aspect, MoreElements);
122 
123   if (MaxLegalElts == 0) {
124     // Scalarize if there's no legal vector type, which is just a special case
125     // of FewerElements.
126     return std::make_pair(FewerElements, EltTy);
127   }
128 
129   return findLegalAction(Aspect, FewerElements);
130 }
131 
132 std::tuple<LegalizerInfo::LegalizeAction, unsigned, LLT>
133 LegalizerInfo::getAction(const MachineInstr &MI,
134                          const MachineRegisterInfo &MRI) const {
135   SmallBitVector SeenTypes(8);
136   const MCOperandInfo *OpInfo = MI.getDesc().OpInfo;
137   for (unsigned i = 0; i < MI.getDesc().getNumOperands(); ++i) {
138     if (!OpInfo[i].isGenericType())
139       continue;
140 
141     // We don't want to repeatedly check the same operand index, that
142     // could get expensive.
143     unsigned TypeIdx = OpInfo[i].getGenericTypeIndex();
144     if (SeenTypes[TypeIdx])
145       continue;
146 
147     SeenTypes.set(TypeIdx);
148 
149     LLT Ty = MRI.getType(MI.getOperand(i).getReg());
150     auto Action = getAction({MI.getOpcode(), TypeIdx, Ty});
151     if (Action.first != Legal)
152       return std::make_tuple(Action.first, TypeIdx, Action.second);
153   }
154   return std::make_tuple(Legal, 0, LLT{});
155 }
156 
157 bool LegalizerInfo::isLegal(const MachineInstr &MI,
158                             const MachineRegisterInfo &MRI) const {
159   return std::get<0>(getAction(MI, MRI)) == Legal;
160 }
161 
162 LLT LegalizerInfo::findLegalType(const InstrAspect &Aspect,
163                                  LegalizeAction Action) const {
164   switch(Action) {
165   default:
166     llvm_unreachable("Cannot find legal type");
167   case Legal:
168   case Lower:
169   case Libcall:
170   case Custom:
171     return Aspect.Type;
172   case NarrowScalar: {
173     return findLegalType(Aspect,
174                          [&](LLT Ty) -> LLT { return Ty.halfScalarSize(); });
175   }
176   case WidenScalar: {
177     return findLegalType(Aspect, [&](LLT Ty) -> LLT {
178       return Ty.getSizeInBits() < 8 ? LLT::scalar(8) : Ty.doubleScalarSize();
179     });
180   }
181   case FewerElements: {
182     return findLegalType(Aspect,
183                          [&](LLT Ty) -> LLT { return Ty.halfElements(); });
184   }
185   case MoreElements: {
186     return findLegalType(Aspect,
187                          [&](LLT Ty) -> LLT { return Ty.doubleElements(); });
188   }
189   }
190 }
191 
192 bool LegalizerInfo::legalizeCustom(MachineInstr &MI,
193                                    MachineRegisterInfo &MRI,
194                                    MachineIRBuilder &MIRBuilder) const {
195   return false;
196 }
197