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 "MCTargetDesc/MipsBaseInfo.h" 16 #include "MipsAnalyzeImmediate.h" 17 #include "MipsInstrInfo.h" 18 #include "MipsMachineFunction.h" 19 #include "MipsTargetMachine.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/IR/DataLayout.h" 26 #include "llvm/IR/Function.h" 27 #include "llvm/Support/CommandLine.h" 28 #include "llvm/Target/TargetOptions.h" 29 30 using namespace llvm; 31 32 33 //===----------------------------------------------------------------------===// 34 // 35 // Stack Frame Processing methods 36 // +----------------------------+ 37 // 38 // The stack is allocated decrementing the stack pointer on 39 // the first instruction of a function prologue. Once decremented, 40 // all stack references are done thought a positive offset 41 // from the stack/frame pointer, so the stack is considering 42 // to grow up! Otherwise terrible hacks would have to be made 43 // to get this stack ABI compliant :) 44 // 45 // The stack frame required by the ABI (after call): 46 // Offset 47 // 48 // 0 ---------- 49 // 4 Args to pass 50 // . saved $GP (used in PIC) 51 // . Alloca allocations 52 // . Local Area 53 // . CPU "Callee Saved" Registers 54 // . saved FP 55 // . saved RA 56 // . FPU "Callee Saved" Registers 57 // StackSize ----------- 58 // 59 // Offset - offset from sp after stack allocation on function prologue 60 // 61 // The sp is the stack pointer subtracted/added from the stack size 62 // at the Prologue/Epilogue 63 // 64 // References to the previous stack (to obtain arguments) are done 65 // with offsets that exceeds the stack size: (stacksize+(4*(num_arg-1)) 66 // 67 // Examples: 68 // - reference to the actual stack frame 69 // for any local area var there is smt like : FI >= 0, StackOffset: 4 70 // sw REGX, 4(SP) 71 // 72 // - reference to previous stack frame 73 // suppose there's a load to the 5th arguments : FI < 0, StackOffset: 16. 74 // The emitted instruction will be something like: 75 // lw REGX, 16+StackSize(SP) 76 // 77 // Since the total stack size is unknown on LowerFormalArguments, all 78 // stack references (ObjectOffset) created to reference the function 79 // arguments, are negative numbers. This way, on eliminateFrameIndex it's 80 // possible to detect those references and the offsets are adjusted to 81 // their real location. 82 // 83 //===----------------------------------------------------------------------===// 84 create(MipsTargetMachine & TM,const MipsSubtarget & ST)85 const MipsFrameLowering *MipsFrameLowering::create(MipsTargetMachine &TM, 86 const MipsSubtarget &ST) { 87 if (TM.getSubtargetImpl()->inMips16Mode()) 88 return llvm::createMips16FrameLowering(ST); 89 90 return llvm::createMipsSEFrameLowering(ST); 91 } 92 93 // hasFP - Return true if the specified function should have a dedicated frame 94 // pointer register. This is true if the function has variable sized allocas or 95 // if frame pointer elimination is disabled. hasFP(const MachineFunction & MF) const96 bool MipsFrameLowering::hasFP(const MachineFunction &MF) const { 97 const MachineFrameInfo *MFI = MF.getFrameInfo(); 98 return MF.getTarget().Options.DisableFramePointerElim(MF) || 99 MFI->hasVarSizedObjects() || MFI->isFrameAddressTaken(); 100 } 101 estimateStackSize(const MachineFunction & MF) const102 uint64_t MipsFrameLowering::estimateStackSize(const MachineFunction &MF) const { 103 const MachineFrameInfo *MFI = MF.getFrameInfo(); 104 const TargetRegisterInfo &TRI = *MF.getTarget().getRegisterInfo(); 105 106 int64_t Offset = 0; 107 108 // Iterate over fixed sized objects. 109 for (int I = MFI->getObjectIndexBegin(); I != 0; ++I) 110 Offset = std::max(Offset, -MFI->getObjectOffset(I)); 111 112 // Conservatively assume all callee-saved registers will be saved. 113 for (const uint16_t *R = TRI.getCalleeSavedRegs(&MF); *R; ++R) { 114 unsigned Size = TRI.getMinimalPhysRegClass(*R)->getSize(); 115 Offset = RoundUpToAlignment(Offset + Size, Size); 116 } 117 118 unsigned MaxAlign = MFI->getMaxAlignment(); 119 120 // Check that MaxAlign is not zero if there is a stack object that is not a 121 // callee-saved spill. 122 assert(!MFI->getObjectIndexEnd() || MaxAlign); 123 124 // Iterate over other objects. 125 for (unsigned I = 0, E = MFI->getObjectIndexEnd(); I != E; ++I) 126 Offset = RoundUpToAlignment(Offset + MFI->getObjectSize(I), MaxAlign); 127 128 // Call frame. 129 if (MFI->adjustsStack() && hasReservedCallFrame(MF)) 130 Offset = RoundUpToAlignment(Offset + MFI->getMaxCallFrameSize(), 131 std::max(MaxAlign, getStackAlignment())); 132 133 return RoundUpToAlignment(Offset, getStackAlignment()); 134 } 135