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   DefaultActions[TargetOpcode::G_IMPLICIT_DEF] = NarrowScalar;
39 
40   // FIXME: these two can be legalized to the fundamental load/store Jakob
41   // proposed. Once loads & stores are supported.
42   DefaultActions[TargetOpcode::G_ANYEXT] = Legal;
43   DefaultActions[TargetOpcode::G_TRUNC] = Legal;
44 
45   DefaultActions[TargetOpcode::G_INTRINSIC] = Legal;
46   DefaultActions[TargetOpcode::G_INTRINSIC_W_SIDE_EFFECTS] = Legal;
47 
48   DefaultActions[TargetOpcode::G_ADD] = NarrowScalar;
49   DefaultActions[TargetOpcode::G_LOAD] = NarrowScalar;
50   DefaultActions[TargetOpcode::G_STORE] = NarrowScalar;
51 
52   DefaultActions[TargetOpcode::G_BRCOND] = WidenScalar;
53   DefaultActions[TargetOpcode::G_INSERT] = NarrowScalar;
54   DefaultActions[TargetOpcode::G_EXTRACT] = NarrowScalar;
55   DefaultActions[TargetOpcode::G_FNEG] = Lower;
56 }
57 
58 void LegalizerInfo::computeTables() {
59   for (unsigned Opcode = 0; Opcode <= LastOp - FirstOp; ++Opcode) {
60     for (unsigned Idx = 0; Idx != Actions[Opcode].size(); ++Idx) {
61       for (auto &Action : Actions[Opcode][Idx]) {
62         LLT Ty = Action.first;
63         if (!Ty.isVector())
64           continue;
65 
66         auto &Entry = MaxLegalVectorElts[std::make_pair(Opcode + FirstOp,
67                                                         Ty.getElementType())];
68         Entry = std::max(Entry, Ty.getNumElements());
69       }
70     }
71   }
72 
73   TablesInitialized = true;
74 }
75 
76 // FIXME: inefficient implementation for now. Without ComputeValueVTs we're
77 // probably going to need specialized lookup structures for various types before
78 // we have any hope of doing well with something like <13 x i3>. Even the common
79 // cases should do better than what we have now.
80 std::pair<LegalizerInfo::LegalizeAction, LLT>
81 LegalizerInfo::getAction(const InstrAspect &Aspect) const {
82   assert(TablesInitialized && "backend forgot to call computeTables");
83   // These *have* to be implemented for now, they're the fundamental basis of
84   // how everything else is transformed.
85 
86   // FIXME: the long-term plan calls for expansion in terms of load/store (if
87   // they're not legal).
88   if (Aspect.Opcode == TargetOpcode::G_MERGE_VALUES ||
89       Aspect.Opcode == TargetOpcode::G_UNMERGE_VALUES)
90     return std::make_pair(Legal, Aspect.Type);
91 
92   LLT Ty = Aspect.Type;
93   LegalizeAction Action = findInActions(Aspect);
94   // LegalizerHelper is not able to handle non-power-of-2 types right now, so do
95   // not try to legalize them unless they are marked as Legal or Custom.
96   // FIXME: This is a temporary hack until the general non-power-of-2
97   // legalization works.
98   if (!isPowerOf2_64(Ty.getSizeInBits()) &&
99       !(Action == Legal || Action == Custom))
100     return std::make_pair(Unsupported, LLT());
101 
102   if (Action != NotFound)
103     return findLegalAction(Aspect, Action);
104 
105   unsigned Opcode = Aspect.Opcode;
106   if (!Ty.isVector()) {
107     auto DefaultAction = DefaultActions.find(Aspect.Opcode);
108     if (DefaultAction != DefaultActions.end() && DefaultAction->second == Legal)
109       return std::make_pair(Legal, Ty);
110 
111     if (DefaultAction != DefaultActions.end() && DefaultAction->second == Lower)
112       return std::make_pair(Lower, Ty);
113 
114     if (DefaultAction == DefaultActions.end() ||
115         DefaultAction->second != NarrowScalar)
116       return std::make_pair(Unsupported, LLT());
117     return findLegalAction(Aspect, NarrowScalar);
118   }
119 
120   LLT EltTy = Ty.getElementType();
121   int NumElts = Ty.getNumElements();
122 
123   auto ScalarAction = ScalarInVectorActions.find(std::make_pair(Opcode, EltTy));
124   if (ScalarAction != ScalarInVectorActions.end() &&
125       ScalarAction->second != Legal)
126     return findLegalAction(Aspect, ScalarAction->second);
127 
128   // The element type is legal in principle, but the number of elements is
129   // wrong.
130   auto MaxLegalElts = MaxLegalVectorElts.lookup(std::make_pair(Opcode, EltTy));
131   if (MaxLegalElts > NumElts)
132     return findLegalAction(Aspect, MoreElements);
133 
134   if (MaxLegalElts == 0) {
135     // Scalarize if there's no legal vector type, which is just a special case
136     // of FewerElements.
137     return std::make_pair(FewerElements, EltTy);
138   }
139 
140   return findLegalAction(Aspect, FewerElements);
141 }
142 
143 std::tuple<LegalizerInfo::LegalizeAction, unsigned, LLT>
144 LegalizerInfo::getAction(const MachineInstr &MI,
145                          const MachineRegisterInfo &MRI) const {
146   SmallBitVector SeenTypes(8);
147   const MCOperandInfo *OpInfo = MI.getDesc().OpInfo;
148   for (unsigned i = 0; i < MI.getDesc().getNumOperands(); ++i) {
149     if (!OpInfo[i].isGenericType())
150       continue;
151 
152     // We don't want to repeatedly check the same operand index, that
153     // could get expensive.
154     unsigned TypeIdx = OpInfo[i].getGenericTypeIndex();
155     if (SeenTypes[TypeIdx])
156       continue;
157 
158     SeenTypes.set(TypeIdx);
159 
160     LLT Ty = MRI.getType(MI.getOperand(i).getReg());
161     auto Action = getAction({MI.getOpcode(), TypeIdx, Ty});
162     if (Action.first != Legal)
163       return std::make_tuple(Action.first, TypeIdx, Action.second);
164   }
165   return std::make_tuple(Legal, 0, LLT{});
166 }
167 
168 bool LegalizerInfo::isLegal(const MachineInstr &MI,
169                             const MachineRegisterInfo &MRI) const {
170   return std::get<0>(getAction(MI, MRI)) == Legal;
171 }
172 
173 Optional<LLT> LegalizerInfo::findLegalType(const InstrAspect &Aspect,
174                                  LegalizeAction Action) const {
175   switch(Action) {
176   default:
177     llvm_unreachable("Cannot find legal type");
178   case Legal:
179   case Lower:
180   case Libcall:
181   case Custom:
182     return Aspect.Type;
183   case NarrowScalar: {
184     return findLegalizableSize(
185         Aspect, [&](LLT Ty) -> LLT { return Ty.halfScalarSize(); });
186   }
187   case WidenScalar: {
188     return findLegalizableSize(Aspect, [&](LLT Ty) -> LLT {
189       return Ty.getSizeInBits() < 8 ? LLT::scalar(8) : Ty.doubleScalarSize();
190     });
191   }
192   case FewerElements: {
193     return findLegalizableSize(
194         Aspect, [&](LLT Ty) -> LLT { return Ty.halfElements(); });
195   }
196   case MoreElements: {
197     return findLegalizableSize(
198         Aspect, [&](LLT Ty) -> LLT { return Ty.doubleElements(); });
199   }
200   }
201 }
202 
203 bool LegalizerInfo::legalizeCustom(MachineInstr &MI,
204                                    MachineRegisterInfo &MRI,
205                                    MachineIRBuilder &MIRBuilder) const {
206   return false;
207 }
208