1 //===-- MipsFrameLowering.cpp - Mips Frame Information --------------------===// 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 contains the Mips implementation of TargetFrameLowering class. 11 // 12 //===----------------------------------------------------------------------===// 13 14 #include "MipsFrameLowering.h" 15 #include "MipsAnalyzeImmediate.h" 16 #include "MipsInstrInfo.h" 17 #include "MipsMachineFunction.h" 18 #include "MCTargetDesc/MipsBaseInfo.h" 19 #include "llvm/Function.h" 20 #include "llvm/CodeGen/MachineFrameInfo.h" 21 #include "llvm/CodeGen/MachineFunction.h" 22 #include "llvm/CodeGen/MachineInstrBuilder.h" 23 #include "llvm/CodeGen/MachineModuleInfo.h" 24 #include "llvm/CodeGen/MachineRegisterInfo.h" 25 #include "llvm/Target/TargetData.h" 26 #include "llvm/Target/TargetOptions.h" 27 #include "llvm/Support/CommandLine.h" 28 29 using namespace llvm; 30 31 32 //===----------------------------------------------------------------------===// 33 // 34 // Stack Frame Processing methods 35 // +----------------------------+ 36 // 37 // The stack is allocated decrementing the stack pointer on 38 // the first instruction of a function prologue. Once decremented, 39 // all stack references are done thought a positive offset 40 // from the stack/frame pointer, so the stack is considering 41 // to grow up! Otherwise terrible hacks would have to be made 42 // to get this stack ABI compliant :) 43 // 44 // The stack frame required by the ABI (after call): 45 // Offset 46 // 47 // 0 ---------- 48 // 4 Args to pass 49 // . saved $GP (used in PIC) 50 // . Alloca allocations 51 // . Local Area 52 // . CPU "Callee Saved" Registers 53 // . saved FP 54 // . saved RA 55 // . FPU "Callee Saved" Registers 56 // StackSize ----------- 57 // 58 // Offset - offset from sp after stack allocation on function prologue 59 // 60 // The sp is the stack pointer subtracted/added from the stack size 61 // at the Prologue/Epilogue 62 // 63 // References to the previous stack (to obtain arguments) are done 64 // with offsets that exceeds the stack size: (stacksize+(4*(num_arg-1)) 65 // 66 // Examples: 67 // - reference to the actual stack frame 68 // for any local area var there is smt like : FI >= 0, StackOffset: 4 69 // sw REGX, 4(SP) 70 // 71 // - reference to previous stack frame 72 // suppose there's a load to the 5th arguments : FI < 0, StackOffset: 16. 73 // The emitted instruction will be something like: 74 // lw REGX, 16+StackSize(SP) 75 // 76 // Since the total stack size is unknown on LowerFormalArguments, all 77 // stack references (ObjectOffset) created to reference the function 78 // arguments, are negative numbers. This way, on eliminateFrameIndex it's 79 // possible to detect those references and the offsets are adjusted to 80 // their real location. 81 // 82 //===----------------------------------------------------------------------===// 83 84 // hasFP - Return true if the specified function should have a dedicated frame 85 // pointer register. This is true if the function has variable sized allocas or 86 // if frame pointer elimination is disabled. 87 bool MipsFrameLowering::hasFP(const MachineFunction &MF) const { 88 const MachineFrameInfo *MFI = MF.getFrameInfo(); 89 return MF.getTarget().Options.DisableFramePointerElim(MF) || 90 MFI->hasVarSizedObjects() || MFI->isFrameAddressTaken(); 91 } 92 93 bool MipsFrameLowering::targetHandlesStackFrameRounding() const { 94 return true; 95 } 96 97 void MipsFrameLowering::emitPrologue(MachineFunction &MF) const { 98 MachineBasicBlock &MBB = MF.front(); 99 MachineFrameInfo *MFI = MF.getFrameInfo(); 100 MipsFunctionInfo *MipsFI = MF.getInfo<MipsFunctionInfo>(); 101 const MipsRegisterInfo *RegInfo = 102 static_cast<const MipsRegisterInfo*>(MF.getTarget().getRegisterInfo()); 103 const MipsInstrInfo &TII = 104 *static_cast<const MipsInstrInfo*>(MF.getTarget().getInstrInfo()); 105 MachineBasicBlock::iterator MBBI = MBB.begin(); 106 DebugLoc dl = MBBI != MBB.end() ? MBBI->getDebugLoc() : DebugLoc(); 107 unsigned SP = STI.isABI_N64() ? Mips::SP_64 : Mips::SP; 108 unsigned FP = STI.isABI_N64() ? Mips::FP_64 : Mips::FP; 109 unsigned ZERO = STI.isABI_N64() ? Mips::ZERO_64 : Mips::ZERO; 110 unsigned ADDu = STI.isABI_N64() ? Mips::DADDu : Mips::ADDu; 111 unsigned ADDiu = STI.isABI_N64() ? Mips::DADDiu : Mips::ADDiu; 112 113 // First, compute final stack size. 114 unsigned StackAlign = getStackAlignment(); 115 uint64_t StackSize = MFI->getObjectOffset(MipsFI->getGlobalRegFI()) + 116 StackAlign + RoundUpToAlignment(MFI->getStackSize(), StackAlign); 117 118 // Update stack size 119 MFI->setStackSize(StackSize); 120 121 // No need to allocate space on the stack. 122 if (StackSize == 0 && !MFI->adjustsStack()) return; 123 124 MachineModuleInfo &MMI = MF.getMMI(); 125 std::vector<MachineMove> &Moves = MMI.getFrameMoves(); 126 MachineLocation DstML, SrcML; 127 128 // Adjust stack. 129 if (isInt<16>(-StackSize)) // addi sp, sp, (-stacksize) 130 BuildMI(MBB, MBBI, dl, TII.get(ADDiu), SP).addReg(SP).addImm(-StackSize); 131 else { // Expand immediate that doesn't fit in 16-bit. 132 unsigned ATReg = STI.isABI_N64() ? Mips::AT_64 : Mips::AT; 133 134 MF.getInfo<MipsFunctionInfo>()->setEmitNOAT(); 135 Mips::loadImmediate(-StackSize, STI.isABI_N64(), TII, MBB, MBBI, dl, false, 136 0); 137 BuildMI(MBB, MBBI, dl, TII.get(ADDu), SP).addReg(SP).addReg(ATReg); 138 } 139 140 // emit ".cfi_def_cfa_offset StackSize" 141 MCSymbol *AdjustSPLabel = MMI.getContext().CreateTempSymbol(); 142 BuildMI(MBB, MBBI, dl, 143 TII.get(TargetOpcode::PROLOG_LABEL)).addSym(AdjustSPLabel); 144 DstML = MachineLocation(MachineLocation::VirtualFP); 145 SrcML = MachineLocation(MachineLocation::VirtualFP, -StackSize); 146 Moves.push_back(MachineMove(AdjustSPLabel, DstML, SrcML)); 147 148 const std::vector<CalleeSavedInfo> &CSI = MFI->getCalleeSavedInfo(); 149 150 if (CSI.size()) { 151 // Find the instruction past the last instruction that saves a callee-saved 152 // register to the stack. 153 for (unsigned i = 0; i < CSI.size(); ++i) 154 ++MBBI; 155 156 // Iterate over list of callee-saved registers and emit .cfi_offset 157 // directives. 158 MCSymbol *CSLabel = MMI.getContext().CreateTempSymbol(); 159 BuildMI(MBB, MBBI, dl, 160 TII.get(TargetOpcode::PROLOG_LABEL)).addSym(CSLabel); 161 162 for (std::vector<CalleeSavedInfo>::const_iterator I = CSI.begin(), 163 E = CSI.end(); I != E; ++I) { 164 int64_t Offset = MFI->getObjectOffset(I->getFrameIdx()); 165 unsigned Reg = I->getReg(); 166 167 // If Reg is a double precision register, emit two cfa_offsets, 168 // one for each of the paired single precision registers. 169 if (Mips::AFGR64RegClass.contains(Reg)) { 170 MachineLocation DstML0(MachineLocation::VirtualFP, Offset); 171 MachineLocation DstML1(MachineLocation::VirtualFP, Offset + 4); 172 MachineLocation SrcML0(RegInfo->getSubReg(Reg, Mips::sub_fpeven)); 173 MachineLocation SrcML1(RegInfo->getSubReg(Reg, Mips::sub_fpodd)); 174 175 if (!STI.isLittle()) 176 std::swap(SrcML0, SrcML1); 177 178 Moves.push_back(MachineMove(CSLabel, DstML0, SrcML0)); 179 Moves.push_back(MachineMove(CSLabel, DstML1, SrcML1)); 180 } else { 181 // Reg is either in CPURegs or FGR32. 182 DstML = MachineLocation(MachineLocation::VirtualFP, Offset); 183 SrcML = MachineLocation(Reg); 184 Moves.push_back(MachineMove(CSLabel, DstML, SrcML)); 185 } 186 } 187 } 188 189 // if framepointer enabled, set it to point to the stack pointer. 190 if (hasFP(MF)) { 191 // Insert instruction "move $fp, $sp" at this location. 192 BuildMI(MBB, MBBI, dl, TII.get(ADDu), FP).addReg(SP).addReg(ZERO); 193 194 // emit ".cfi_def_cfa_register $fp" 195 MCSymbol *SetFPLabel = MMI.getContext().CreateTempSymbol(); 196 BuildMI(MBB, MBBI, dl, 197 TII.get(TargetOpcode::PROLOG_LABEL)).addSym(SetFPLabel); 198 DstML = MachineLocation(FP); 199 SrcML = MachineLocation(MachineLocation::VirtualFP); 200 Moves.push_back(MachineMove(SetFPLabel, DstML, SrcML)); 201 } 202 } 203 204 void MipsFrameLowering::emitEpilogue(MachineFunction &MF, 205 MachineBasicBlock &MBB) const { 206 MachineBasicBlock::iterator MBBI = MBB.getLastNonDebugInstr(); 207 MachineFrameInfo *MFI = MF.getFrameInfo(); 208 const MipsInstrInfo &TII = 209 *static_cast<const MipsInstrInfo*>(MF.getTarget().getInstrInfo()); 210 DebugLoc dl = MBBI->getDebugLoc(); 211 unsigned SP = STI.isABI_N64() ? Mips::SP_64 : Mips::SP; 212 unsigned FP = STI.isABI_N64() ? Mips::FP_64 : Mips::FP; 213 unsigned ZERO = STI.isABI_N64() ? Mips::ZERO_64 : Mips::ZERO; 214 unsigned ADDu = STI.isABI_N64() ? Mips::DADDu : Mips::ADDu; 215 unsigned ADDiu = STI.isABI_N64() ? Mips::DADDiu : Mips::ADDiu; 216 217 // if framepointer enabled, restore the stack pointer. 218 if (hasFP(MF)) { 219 // Find the first instruction that restores a callee-saved register. 220 MachineBasicBlock::iterator I = MBBI; 221 222 for (unsigned i = 0; i < MFI->getCalleeSavedInfo().size(); ++i) 223 --I; 224 225 // Insert instruction "move $sp, $fp" at this location. 226 BuildMI(MBB, I, dl, TII.get(ADDu), SP).addReg(FP).addReg(ZERO); 227 } 228 229 // Get the number of bytes from FrameInfo 230 uint64_t StackSize = MFI->getStackSize(); 231 232 if (!StackSize) 233 return; 234 235 // Adjust stack. 236 if (isInt<16>(StackSize)) // addi sp, sp, (-stacksize) 237 BuildMI(MBB, MBBI, dl, TII.get(ADDiu), SP).addReg(SP).addImm(StackSize); 238 else { // Expand immediate that doesn't fit in 16-bit. 239 unsigned ATReg = STI.isABI_N64() ? Mips::AT_64 : Mips::AT; 240 241 MF.getInfo<MipsFunctionInfo>()->setEmitNOAT(); 242 Mips::loadImmediate(StackSize, STI.isABI_N64(), TII, MBB, MBBI, dl, false, 243 0); 244 BuildMI(MBB, MBBI, dl, TII.get(ADDu), SP).addReg(SP).addReg(ATReg); 245 } 246 } 247 248 void MipsFrameLowering:: 249 processFunctionBeforeCalleeSavedScan(MachineFunction &MF, 250 RegScavenger *RS) const { 251 MachineRegisterInfo& MRI = MF.getRegInfo(); 252 unsigned FP = STI.isABI_N64() ? Mips::FP_64 : Mips::FP; 253 254 // FIXME: remove this code if register allocator can correctly mark 255 // $fp and $ra used or unused. 256 257 // Mark $fp and $ra as used or unused. 258 if (hasFP(MF)) 259 MRI.setPhysRegUsed(FP); 260 261 // The register allocator might determine $ra is used after seeing 262 // instruction "jr $ra", but we do not want PrologEpilogInserter to insert 263 // instructions to save/restore $ra unless there is a function call. 264 // To correct this, $ra is explicitly marked unused if there is no 265 // function call. 266 if (MF.getFrameInfo()->hasCalls()) 267 MRI.setPhysRegUsed(Mips::RA); 268 else { 269 MRI.setPhysRegUnused(Mips::RA); 270 MRI.setPhysRegUnused(Mips::RA_64); 271 } 272 } 273