AArch64Subtarget.cpp revision 288943 
1//===-- AArch64Subtarget.cpp - AArch64 Subtarget Information ----*- C++ -*-===//
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// This file implements the AArch64 specific subclass of TargetSubtarget.
11//
12//===----------------------------------------------------------------------===//
13
14#include "AArch64InstrInfo.h"
15#include "AArch64PBQPRegAlloc.h"
16#include "AArch64Subtarget.h"
17#include "llvm/ADT/SmallVector.h"
18#include "llvm/CodeGen/MachineScheduler.h"
19#include "llvm/IR/GlobalValue.h"
20#include "llvm/Support/TargetRegistry.h"
21
22using namespace llvm;
23
24#define DEBUG_TYPE "aarch64-subtarget"
25
26#define GET_SUBTARGETINFO_CTOR
27#define GET_SUBTARGETINFO_TARGET_DESC
28#include "AArch64GenSubtargetInfo.inc"
29
30static cl::opt<bool>
31EnableEarlyIfConvert("aarch64-early-ifcvt", cl::desc("Enable the early if "
32                     "converter pass"), cl::init(true), cl::Hidden);
33
34AArch64Subtarget &
35AArch64Subtarget::initializeSubtargetDependencies(StringRef FS) {
36  // Determine default and user-specified characteristics
37
38  if (CPUString.empty())
39    CPUString = "generic";
40
41  ParseSubtargetFeatures(CPUString, FS);
42  return *this;
43}
44
45AArch64Subtarget::AArch64Subtarget(const Triple &TT, const std::string &CPU,
46                                   const std::string &FS,
47                                   const TargetMachine &TM, bool LittleEndian)
48    : AArch64GenSubtargetInfo(TT, CPU, FS), ARMProcFamily(Others),
49      HasV8_1aOps(false), HasFPARMv8(false), HasNEON(false), HasCrypto(false),
50      HasCRC(false), HasZeroCycleRegMove(false), HasZeroCycleZeroing(false),
51      IsLittle(LittleEndian), CPUString(CPU), TargetTriple(TT), FrameLowering(),
52      InstrInfo(initializeSubtargetDependencies(FS)), TSInfo(),
53      TLInfo(TM, *this) {}
54
55/// ClassifyGlobalReference - Find the target operand flags that describe
56/// how a global value should be referenced for the current subtarget.
57unsigned char
58AArch64Subtarget::ClassifyGlobalReference(const GlobalValue *GV,
59                                        const TargetMachine &TM) const {
60  bool isDef = GV->isStrongDefinitionForLinker();
61
62  // MachO large model always goes via a GOT, simply to get a single 8-byte
63  // absolute relocation on all global addresses.
64  if (TM.getCodeModel() == CodeModel::Large && isTargetMachO())
65    return AArch64II::MO_GOT;
66
67  // The small code mode's direct accesses use ADRP, which cannot necessarily
68  // produce the value 0 (if the code is above 4GB).
69  if (TM.getCodeModel() == CodeModel::Small && GV->hasExternalWeakLinkage()) {
70    // In PIC mode use the GOT, but in absolute mode use a constant pool load.
71    if (TM.getRelocationModel() == Reloc::Static)
72        return AArch64II::MO_CONSTPOOL;
73    else
74        return AArch64II::MO_GOT;
75  }
76
77  // If symbol visibility is hidden, the extra load is not needed if
78  // the symbol is definitely defined in the current translation unit.
79
80  // The handling of non-hidden symbols in PIC mode is rather target-dependent:
81  //   + On MachO, if the symbol is defined in this module the GOT can be
82  //     skipped.
83  //   + On ELF, the R_AARCH64_COPY relocation means that even symbols actually
84  //     defined could end up in unexpected places. Use a GOT.
85  if (TM.getRelocationModel() != Reloc::Static && GV->hasDefaultVisibility()) {
86    if (isTargetMachO())
87      return isDef ? AArch64II::MO_NO_FLAG : AArch64II::MO_GOT;
88    else
89      // No need to go through the GOT for local symbols on ELF.
90      return GV->hasLocalLinkage() ? AArch64II::MO_NO_FLAG : AArch64II::MO_GOT;
91  }
92
93  return AArch64II::MO_NO_FLAG;
94}
95
96/// This function returns the name of a function which has an interface
97/// like the non-standard bzero function, if such a function exists on
98/// the current subtarget and it is considered prefereable over
99/// memset with zero passed as the second argument. Otherwise it
100/// returns null.
101const char *AArch64Subtarget::getBZeroEntry() const {
102  // Prefer bzero on Darwin only.
103  if(isTargetDarwin())
104    return "bzero";
105
106  return nullptr;
107}
108
109void AArch64Subtarget::overrideSchedPolicy(MachineSchedPolicy &Policy,
110                                         MachineInstr *begin, MachineInstr *end,
111                                         unsigned NumRegionInstrs) const {
112  // LNT run (at least on Cyclone) showed reasonably significant gains for
113  // bi-directional scheduling. 253.perlbmk.
114  Policy.OnlyTopDown = false;
115  Policy.OnlyBottomUp = false;
116}
117
118bool AArch64Subtarget::enableEarlyIfConversion() const {
119  return EnableEarlyIfConvert;
120}
121
122std::unique_ptr<PBQPRAConstraint>
123AArch64Subtarget::getCustomPBQPConstraints() const {
124  if (!isCortexA57())
125    return nullptr;
126
127  return llvm::make_unique<A57ChainingConstraint>();
128}
129