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 #include "llvm/ADT/SmallBitVector.h"
22 #include "llvm/CodeGen/MachineInstr.h"
23 #include "llvm/CodeGen/MachineOperand.h"
24 #include "llvm/CodeGen/MachineRegisterInfo.h"
25 #include "llvm/MC/MCInstrDesc.h"
26 #include "llvm/Support/ErrorHandling.h"
27 #include "llvm/Support/LowLevelTypeImpl.h"
28 #include "llvm/Support/MathExtras.h"
29 #include "llvm/Target/TargetOpcodes.h"
30 #include <algorithm>
31 #include <cassert>
32 #include <tuple>
33 #include <utility>
34 
35 using namespace llvm;
36 
37 LegalizerInfo::LegalizerInfo() {
38   // FIXME: these two can be legalized to the fundamental load/store Jakob
39   // proposed. Once loads & stores are supported.
40   DefaultActions[TargetOpcode::G_ANYEXT] = Legal;
41   DefaultActions[TargetOpcode::G_TRUNC] = Legal;
42 
43   DefaultActions[TargetOpcode::G_INTRINSIC] = Legal;
44   DefaultActions[TargetOpcode::G_INTRINSIC_W_SIDE_EFFECTS] = Legal;
45 
46   DefaultActions[TargetOpcode::G_ADD] = NarrowScalar;
47   DefaultActions[TargetOpcode::G_LOAD] = NarrowScalar;
48   DefaultActions[TargetOpcode::G_STORE] = NarrowScalar;
49 
50   DefaultActions[TargetOpcode::G_BRCOND] = WidenScalar;
51   DefaultActions[TargetOpcode::G_INSERT] = NarrowScalar;
52   DefaultActions[TargetOpcode::G_EXTRACT] = NarrowScalar;
53   DefaultActions[TargetOpcode::G_FNEG] = Lower;
54 }
55 
56 void LegalizerInfo::computeTables() {
57   for (unsigned Opcode = 0; Opcode <= LastOp - FirstOp; ++Opcode) {
58     for (unsigned Idx = 0; Idx != Actions[Opcode].size(); ++Idx) {
59       for (auto &Action : Actions[Opcode][Idx]) {
60         LLT Ty = Action.first;
61         if (!Ty.isVector())
62           continue;
63 
64         auto &Entry = MaxLegalVectorElts[std::make_pair(Opcode + FirstOp,
65                                                         Ty.getElementType())];
66         Entry = std::max(Entry, Ty.getNumElements());
67       }
68     }
69   }
70 
71   TablesInitialized = true;
72 }
73 
74 // FIXME: inefficient implementation for now. Without ComputeValueVTs we're
75 // probably going to need specialized lookup structures for various types before
76 // we have any hope of doing well with something like <13 x i3>. Even the common
77 // cases should do better than what we have now.
78 std::pair<LegalizerInfo::LegalizeAction, LLT>
79 LegalizerInfo::getAction(const InstrAspect &Aspect) const {
80   assert(TablesInitialized && "backend forgot to call computeTables");
81   // These *have* to be implemented for now, they're the fundamental basis of
82   // how everything else is transformed.
83 
84   // FIXME: the long-term plan calls for expansion in terms of load/store (if
85   // they're not legal).
86   if (Aspect.Opcode == TargetOpcode::G_MERGE_VALUES ||
87       Aspect.Opcode == TargetOpcode::G_UNMERGE_VALUES)
88     return std::make_pair(Legal, Aspect.Type);
89 
90   LLT Ty = Aspect.Type;
91   LegalizeAction Action = findInActions(Aspect);
92   // LegalizerHelper is not able to handle non-power-of-2 types right now, so do
93   // not try to legalize them unless they are marked as Legal or Custom.
94   // FIXME: This is a temporary hack until the general non-power-of-2
95   // legalization works.
96   if (!isPowerOf2_64(Ty.getSizeInBits()) &&
97       !(Action == Legal || Action == Custom))
98     return std::make_pair(Unsupported, LLT());
99 
100   if (Action != NotFound)
101     return findLegalAction(Aspect, Action);
102 
103   unsigned Opcode = Aspect.Opcode;
104   if (!Ty.isVector()) {
105     auto DefaultAction = DefaultActions.find(Aspect.Opcode);
106     if (DefaultAction != DefaultActions.end() && DefaultAction->second == Legal)
107       return std::make_pair(Legal, Ty);
108 
109     if (DefaultAction != DefaultActions.end() && DefaultAction->second == Lower)
110       return std::make_pair(Lower, Ty);
111 
112     if (DefaultAction == DefaultActions.end() ||
113         DefaultAction->second != NarrowScalar)
114       return std::make_pair(Unsupported, LLT());
115     return findLegalAction(Aspect, NarrowScalar);
116   }
117 
118   LLT EltTy = Ty.getElementType();
119   int NumElts = Ty.getNumElements();
120 
121   auto ScalarAction = ScalarInVectorActions.find(std::make_pair(Opcode, EltTy));
122   if (ScalarAction != ScalarInVectorActions.end() &&
123       ScalarAction->second != Legal)
124     return findLegalAction(Aspect, ScalarAction->second);
125 
126   // The element type is legal in principle, but the number of elements is
127   // wrong.
128   auto MaxLegalElts = MaxLegalVectorElts.lookup(std::make_pair(Opcode, EltTy));
129   if (MaxLegalElts > NumElts)
130     return findLegalAction(Aspect, MoreElements);
131 
132   if (MaxLegalElts == 0) {
133     // Scalarize if there's no legal vector type, which is just a special case
134     // of FewerElements.
135     return std::make_pair(FewerElements, EltTy);
136   }
137 
138   return findLegalAction(Aspect, FewerElements);
139 }
140 
141 std::tuple<LegalizerInfo::LegalizeAction, unsigned, LLT>
142 LegalizerInfo::getAction(const MachineInstr &MI,
143                          const MachineRegisterInfo &MRI) const {
144   SmallBitVector SeenTypes(8);
145   const MCOperandInfo *OpInfo = MI.getDesc().OpInfo;
146   for (unsigned i = 0; i < MI.getDesc().getNumOperands(); ++i) {
147     if (!OpInfo[i].isGenericType())
148       continue;
149 
150     // We don't want to repeatedly check the same operand index, that
151     // could get expensive.
152     unsigned TypeIdx = OpInfo[i].getGenericTypeIndex();
153     if (SeenTypes[TypeIdx])
154       continue;
155 
156     SeenTypes.set(TypeIdx);
157 
158     LLT Ty = MRI.getType(MI.getOperand(i).getReg());
159     auto Action = getAction({MI.getOpcode(), TypeIdx, Ty});
160     if (Action.first != Legal)
161       return std::make_tuple(Action.first, TypeIdx, Action.second);
162   }
163   return std::make_tuple(Legal, 0, LLT{});
164 }
165 
166 bool LegalizerInfo::isLegal(const MachineInstr &MI,
167                             const MachineRegisterInfo &MRI) const {
168   return std::get<0>(getAction(MI, MRI)) == Legal;
169 }
170 
171 Optional<LLT> LegalizerInfo::findLegalType(const InstrAspect &Aspect,
172                                  LegalizeAction Action) const {
173   switch(Action) {
174   default:
175     llvm_unreachable("Cannot find legal type");
176   case Legal:
177   case Lower:
178   case Libcall:
179   case Custom:
180     return Aspect.Type;
181   case NarrowScalar:
182     return findLegalType(Aspect,
183                          [](LLT Ty) -> LLT { return Ty.halfScalarSize(); });
184   case WidenScalar:
185     return findLegalType(Aspect, [](LLT Ty) -> LLT {
186       return Ty.getSizeInBits() < 8 ? LLT::scalar(8) : Ty.doubleScalarSize();
187     });
188   case FewerElements:
189     return findLegalType(Aspect,
190                          [](LLT Ty) -> LLT { return Ty.halfElements(); });
191   case MoreElements:
192     return findLegalType(Aspect,
193                          [](LLT Ty) -> LLT { return Ty.doubleElements(); });
194   }
195 }
196 
197 bool LegalizerInfo::legalizeCustom(MachineInstr &MI,
198                                    MachineRegisterInfo &MRI,
199                                    MachineIRBuilder &MIRBuilder) const {
200   return false;
201 }
202