llvm/lib/Target/M68k/M68kSubtarget.cpp

   1 //===-- M68kSubtarget.cpp - M68k Subtarget Information ----------*- C++ -*-===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8 ///
   9 /// \file
  10 /// This file implements the M68k specific subclass of TargetSubtargetInfo.
  11 ///
  12 //===----------------------------------------------------------------------===//
  13
  14 #include "M68kSubtarget.h"
  15 #include "GISel/M68kCallLowering.h"
  16 #include "GISel/M68kLegalizerInfo.h"
  17 #include "GISel/M68kRegisterBankInfo.h"
  18
  19 #include "M68k.h"
  20 #include "M68kMachineFunction.h"
  21 #include "M68kRegisterInfo.h"
  22 #include "M68kTargetMachine.h"
  23
  24 #include "llvm/CodeGen/MachineJumpTableInfo.h"
  25 #include "llvm/IR/Attributes.h"
  26 #include "llvm/IR/Function.h"
  27 #include "llvm/MC/TargetRegistry.h"
  28 #include "llvm/Support/CommandLine.h"
  29 #include "llvm/Support/ErrorHandling.h"
  30
  31 using namespace llvm;
  32
  33 #define DEBUG_TYPE "m68k-subtarget"
  34
  35 #define GET_SUBTARGETINFO_TARGET_DESC
  36 #define GET_SUBTARGETINFO_CTOR
  37 #include "M68kGenSubtargetInfo.inc"
  38
  39 extern bool FixGlobalBaseReg;
  40
  41 /// Select the M68k CPU for the given triple and cpu name.
  42 static StringRef selectM68kCPU(Triple TT, StringRef CPU) {
  43   if (CPU.empty() || CPU == "generic") {
  44     CPU = "M68000";
  45   }
  46   return CPU;
  47 }
  48
  49 void M68kSubtarget::anchor() {}
  50
  51 M68kSubtarget::M68kSubtarget(const Triple &TT, StringRef CPU, StringRef FS,
  52                              const M68kTargetMachine &TM)
  53     : M68kGenSubtargetInfo(TT, CPU, /*TuneCPU*/ CPU, FS), TM(TM), TSInfo(),
  54       InstrInfo(initializeSubtargetDependencies(CPU, TT, FS, TM)),
  55       FrameLowering(*this, this->getStackAlignment()), TLInfo(TM, *this),
  56       TargetTriple(TT) {
  57   CallLoweringInfo.reset(new M68kCallLowering(*getTargetLowering()));
  58   Legalizer.reset(new M68kLegalizerInfo(*this));
  59
  60   auto *RBI = new M68kRegisterBankInfo(*getRegisterInfo());
  61   RegBankInfo.reset(RBI);
  62   InstSelector.reset(createM68kInstructionSelector(TM, *this, *RBI));
  63 }
  64
  65 const CallLowering *M68kSubtarget::getCallLowering() const {
  66   return CallLoweringInfo.get();
  67 }
  68
  69 InstructionSelector *M68kSubtarget::getInstructionSelector() const {
  70   return InstSelector.get();
  71 }
  72
  73 const LegalizerInfo *M68kSubtarget::getLegalizerInfo() const {
  74   return Legalizer.get();
  75 }
  76
  77 const RegisterBankInfo *M68kSubtarget::getRegBankInfo() const {
  78   return RegBankInfo.get();
  79 }
  80
  81 bool M68kSubtarget::isPositionIndependent() const {
  82   return TM.isPositionIndependent();
  83 }
  84
  85 bool M68kSubtarget::isLegalToCallImmediateAddr() const { return true; }
  86
  87 M68kSubtarget &M68kSubtarget::initializeSubtargetDependencies(
  88     StringRef CPU, Triple TT, StringRef FS, const M68kTargetMachine &TM) {
  89   std::string CPUName = selectM68kCPU(TT, CPU).str();
  90
  91   // Parse features string.
  92   ParseSubtargetFeatures(CPUName, CPUName, FS);
  93
  94   // Initialize scheduling itinerary for the specified CPU.
  95   InstrItins = getInstrItineraryForCPU(CPUName);
  96
  97   stackAlignment = 8;
  98
  99   return *this;
 100 }
 101
 102 //===----------------------------------------------------------------------===//
 103 // Code Model
 104 //
 105 // Key assumptions:
 106 //  - Whenever possible we use pc-rel encoding since it is smaller(16 bit) than
 107 //    absolute(32 bit).
 108 //  - GOT is reachable within 16 bit offset for both Small and Medium models.
 109 //  - Code section is reachable within 16 bit offset for both models.
 110 //
 111 //  ---------------------+-------------------------+--------------------------
 112 //                       |          Small          |          Medium
 113 //                       +-------------------------+------------+-------------
 114 //                       |   Static   |    PIC     |   Static   |    PIC
 115 //  ---------------------+------------+------------+------------+-------------
 116 //                branch |   pc-rel   |   pc-rel   |   pc-rel   |   pc-rel
 117 //  ---------------------+------------+------------+------------+-------------
 118 //           call global |    @PLT    |    @PLT    |    @PLT    |    @PLT
 119 //  ---------------------+------------+------------+------------+-------------
 120 //         call internal |   pc-rel   |   pc-rel   |   pc-rel   |   pc-rel
 121 //  ---------------------+------------+------------+------------+-------------
 122 //            data local |   pc-rel   |   pc-rel   |  ~pc-rel   |  ^pc-rel
 123 //  ---------------------+------------+------------+------------+-------------
 124 //       data local big* |   pc-rel   |   pc-rel   |  absolute  |  @GOTOFF
 125 //  ---------------------+------------+------------+------------+-------------
 126 //           data global |   pc-rel   |  @GOTPCREL |  ~pc-rel   |  @GOTPCREL
 127 //  ---------------------+------------+------------+------------+-------------
 128 //      data global big* |   pc-rel   |  @GOTPCREL |  absolute  |  @GOTPCREL
 129 //  ---------------------+------------+------------+------------+-------------
 130 //
 131 // * Big data potentially cannot be reached within 16 bit offset and requires
 132 //   special handling for old(x00 and x10) CPUs. Normally these symbols go into
 133 //   separate .ldata section which mapped after normal .data and .text, but I
 134 //   don't really know how this must be done for M68k atm... will try to dig
 135 //   this info out from GCC. For now CPUs prior to M68020 will use static ref
 136 //   for Static Model and @GOT based references for PIC.
 137 //
 138 // ~ These are absolute for older CPUs for now.
 139 // ^ These are @GOTOFF for older CPUs for now.
 140 //===----------------------------------------------------------------------===//
 141
 142 /// Classify a blockaddress reference for the current subtarget according to how
 143 /// we should reference it in a non-pcrel context.
 144 unsigned char M68kSubtarget::classifyBlockAddressReference() const {
 145   // Unless we start to support Large Code Model branching is always pc-rel
 146   return M68kII::MO_PC_RELATIVE_ADDRESS;
 147 }
 148
 149 unsigned char
 150 M68kSubtarget::classifyLocalReference(const GlobalValue *GV) const {
 151   switch (TM.getCodeModel()) {
 152   default:
 153     llvm_unreachable("Unsupported code model");
 154   case CodeModel::Small:
 155   case CodeModel::Kernel: {
 156     return M68kII::MO_PC_RELATIVE_ADDRESS;
 157   }
 158   case CodeModel::Medium: {
 159     if (isPositionIndependent()) {
 160       // On M68020 and better we can fit big any data offset into dips field.
 161       if (atLeastM68020()) {
 162         return M68kII::MO_PC_RELATIVE_ADDRESS;
 163       }
 164       // Otherwise we could check the data size and make sure it will fit into
 165       // 16 bit offset. For now we will be conservative and go with @GOTOFF
 166       return M68kII::MO_GOTOFF;
 167     } else {
 168       if (atLeastM68020()) {
 169         return M68kII::MO_PC_RELATIVE_ADDRESS;
 170       }
 171       return M68kII::MO_ABSOLUTE_ADDRESS;
 172     }
 173   }
 174   }
 175 }
 176
 177 unsigned char M68kSubtarget::classifyExternalReference(const Module &M) const {
 178   if (TM.shouldAssumeDSOLocal(M, nullptr))
 179     return classifyLocalReference(nullptr);
 180
 181   if (isPositionIndependent())
 182     return M68kII::MO_GOTPCREL;
 183
 184   return M68kII::MO_GOT;
 185 }
 186
 187 unsigned char
 188 M68kSubtarget::classifyGlobalReference(const GlobalValue *GV) const {
 189   return classifyGlobalReference(GV, *GV->getParent());
 190 }
 191
 192 unsigned char M68kSubtarget::classifyGlobalReference(const GlobalValue *GV,
 193                                                      const Module &M) const {
 194   if (TM.shouldAssumeDSOLocal(M, GV))
 195     return classifyLocalReference(GV);
 196
 197   switch (TM.getCodeModel()) {
 198   default:
 199     llvm_unreachable("Unsupported code model");
 200   case CodeModel::Small:
 201   case CodeModel::Kernel: {
 202     if (isPositionIndependent())
 203       return M68kII::MO_GOTPCREL;
 204     return M68kII::MO_PC_RELATIVE_ADDRESS;
 205   }
 206   case CodeModel::Medium: {
 207     if (isPositionIndependent())
 208       return M68kII::MO_GOTPCREL;
 209
 210     if (atLeastM68020())
 211       return M68kII::MO_PC_RELATIVE_ADDRESS;
 212
 213     return M68kII::MO_ABSOLUTE_ADDRESS;
 214   }
 215   }
 216 }
 217
 218 unsigned M68kSubtarget::getJumpTableEncoding() const {
 219   if (isPositionIndependent()) {
 220     // The only time we want to use GOTOFF(used when with EK_Custom32) is when
 221     // the potential delta between the jump target and table base can be larger
 222     // than displacement field, which is True for older CPUs(16 bit disp)
 223     // in Medium model(can have large data way beyond 16 bit).
 224     if (TM.getCodeModel() == CodeModel::Medium && !atLeastM68020())
 225       return MachineJumpTableInfo::EK_Custom32;
 226
 227     return MachineJumpTableInfo::EK_LabelDifference32;
 228   }
 229
 230   // In non-pic modes, just use the address of a block.
 231   return MachineJumpTableInfo::EK_BlockAddress;
 232 }
 233
 234 unsigned char
 235 M68kSubtarget::classifyGlobalFunctionReference(const GlobalValue *GV) const {
 236   return classifyGlobalFunctionReference(GV, *GV->getParent());
 237 }
 238
 239 unsigned char
 240 M68kSubtarget::classifyGlobalFunctionReference(const GlobalValue *GV,
 241                                                const Module &M) const {
 242   // local always use pc-rel referencing
 243   if (TM.shouldAssumeDSOLocal(M, GV))
 244     return M68kII::MO_NO_FLAG;
 245
 246   // If the function is marked as non-lazy, generate an indirect call
 247   // which loads from the GOT directly. This avoids run-time overhead
 248   // at the cost of eager binding.
 249   auto *F = dyn_cast_or_null<Function>(GV);
 250   if (F && F->hasFnAttribute(Attribute::NonLazyBind)) {
 251     return M68kII::MO_GOTPCREL;
 252   }
 253
 254   // otherwise linker will figure this out
 255   return M68kII::MO_PLT;
 256 }