llvm/lib/CodeGen/TargetFrameLoweringImpl.cpp

   1 //===- TargetFrameLoweringImpl.cpp - Implement target frame interface ------==//
   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 // Implements the layout of a stack frame on the target machine.
  10 //
  11 //===----------------------------------------------------------------------===//
  12
  13 #include "llvm/ADT/BitVector.h"
  14 #include "llvm/CodeGen/MachineFrameInfo.h"
  15 #include "llvm/CodeGen/MachineFunction.h"
  16 #include "llvm/CodeGen/MachineRegisterInfo.h"
  17 #include "llvm/CodeGen/TargetFrameLowering.h"
  18 #include "llvm/CodeGen/TargetSubtargetInfo.h"
  19 #include "llvm/IR/Attributes.h"
  20 #include "llvm/IR/Function.h"
  21 #include "llvm/IR/InstrTypes.h"
  22 #include "llvm/MC/MCAsmInfo.h"
  23 #include "llvm/Support/Compiler.h"
  24 #include "llvm/Target/TargetMachine.h"
  25 #include "llvm/Target/TargetOptions.h"
  26
  27 using namespace llvm;
  28
  29 TargetFrameLowering::~TargetFrameLowering() = default;
  30
  31 bool TargetFrameLowering::enableCalleeSaveSkip(const MachineFunction &MF) const {
  32   assert(MF.getFunction().hasFnAttribute(Attribute::NoReturn) &&
  33          MF.getFunction().hasFnAttribute(Attribute::NoUnwind) &&
  34          !MF.getFunction().hasFnAttribute(Attribute::UWTable));
  35   return false;
  36 }
  37
  38 bool TargetFrameLowering::enableCFIFixup(MachineFunction &MF) const {
  39   return MF.needsFrameMoves() &&
  40          !MF.getTarget().getMCAsmInfo()->usesWindowsCFI();
  41 }
  42
  43 /// Returns the displacement from the frame register to the stack
  44 /// frame of the specified index, along with the frame register used
  45 /// (in output arg FrameReg). This is the default implementation which
  46 /// is overridden for some targets.
  47 StackOffset
  48 TargetFrameLowering::getFrameIndexReference(const MachineFunction &MF, int FI,
  49                                             Register &FrameReg) const {
  50   const MachineFrameInfo &MFI = MF.getFrameInfo();
  51   const TargetRegisterInfo *RI = MF.getSubtarget().getRegisterInfo();
  52
  53   // By default, assume all frame indices are referenced via whatever
  54   // getFrameRegister() says. The target can override this if it's doing
  55   // something different.
  56   FrameReg = RI->getFrameRegister(MF);
  57
  58   return StackOffset::getFixed(MFI.getObjectOffset(FI) + MFI.getStackSize() -
  59                                getOffsetOfLocalArea() +
  60                                MFI.getOffsetAdjustment());
  61 }
  62
  63 /// Returns the offset from the stack pointer to the slot of the specified
  64 /// index. This function serves to provide a comparable offset from a single
  65 /// reference point (the value of the stack-pointer at function entry) that can
  66 /// be used for analysis. This is the default implementation using
  67 /// MachineFrameInfo offsets.
  68 StackOffset
  69 TargetFrameLowering::getFrameIndexReferenceFromSP(const MachineFunction &MF,
  70                                                   int FI) const {
  71   // To display the true offset from SP, we need to subtract the offset to the
  72   // local area from MFI's ObjectOffset.
  73   return StackOffset::getFixed(MF.getFrameInfo().getObjectOffset(FI) -
  74                                getOffsetOfLocalArea());
  75 }
  76
  77 bool TargetFrameLowering::needsFrameIndexResolution(
  78     const MachineFunction &MF) const {
  79   return MF.getFrameInfo().hasStackObjects();
  80 }
  81
  82 void TargetFrameLowering::getCalleeSaves(const MachineFunction &MF,
  83                                          BitVector &CalleeSaves) const {
  84   const TargetRegisterInfo &TRI = *MF.getSubtarget().getRegisterInfo();
  85   CalleeSaves.resize(TRI.getNumRegs());
  86
  87   const MachineFrameInfo &MFI = MF.getFrameInfo();
  88   if (!MFI.isCalleeSavedInfoValid())
  89     return;
  90
  91   for (const CalleeSavedInfo &Info : MFI.getCalleeSavedInfo())
  92     CalleeSaves.set(Info.getReg());
  93 }
  94
  95 void TargetFrameLowering::determineCalleeSaves(MachineFunction &MF,
  96                                                BitVector &SavedRegs,
  97                                                RegScavenger *RS) const {
  98   const TargetRegisterInfo &TRI = *MF.getSubtarget().getRegisterInfo();
  99
 100   // Resize before the early returns. Some backends expect that
 101   // SavedRegs.size() == TRI.getNumRegs() after this call even if there are no
 102   // saved registers.
 103   SavedRegs.resize(TRI.getNumRegs());
 104
 105   // Get the callee saved register list...
 106   const MCPhysReg *CSRegs = nullptr;
 107
 108   // When interprocedural register allocation is enabled, callee saved register
 109   // list should be empty, since caller saved registers are preferred over
 110   // callee saved registers. Unless it has some risked CSR to be optimized out.
 111   if (MF.getTarget().Options.EnableIPRA &&
 112       isSafeForNoCSROpt(MF.getFunction()) &&
 113       isProfitableForNoCSROpt(MF.getFunction()))
 114     CSRegs = TRI.getIPRACSRegs(&MF);
 115   else
 116     CSRegs = MF.getRegInfo().getCalleeSavedRegs();
 117
 118   // Early exit if there are no callee saved registers.
 119   if (!CSRegs || CSRegs[0] == 0)
 120     return;
 121
 122   // In Naked functions we aren't going to save any registers.
 123   if (MF.getFunction().hasFnAttribute(Attribute::Naked))
 124     return;
 125
 126   // Noreturn+nounwind functions never restore CSR, so no saves are needed.
 127   // Purely noreturn functions may still return through throws, so those must
 128   // save CSR for caller exception handlers.
 129   //
 130   // If the function uses longjmp to break out of its current path of
 131   // execution we do not need the CSR spills either: setjmp stores all CSRs
 132   // it was called with into the jmp_buf, which longjmp then restores.
 133   if (MF.getFunction().hasFnAttribute(Attribute::NoReturn) &&
 134         MF.getFunction().hasFnAttribute(Attribute::NoUnwind) &&
 135         !MF.getFunction().hasFnAttribute(Attribute::UWTable) &&
 136         enableCalleeSaveSkip(MF))
 137     return;
 138
 139   // Functions which call __builtin_unwind_init get all their registers saved.
 140   bool CallsUnwindInit = MF.callsUnwindInit();
 141   const MachineRegisterInfo &MRI = MF.getRegInfo();
 142   for (unsigned i = 0; CSRegs[i]; ++i) {
 143     unsigned Reg = CSRegs[i];
 144     if (CallsUnwindInit || MRI.isPhysRegModified(Reg))
 145       SavedRegs.set(Reg);
 146   }
 147 }
 148
 149 bool TargetFrameLowering::allocateScavengingFrameIndexesNearIncomingSP(
 150   const MachineFunction &MF) const {
 151   if (!hasFP(MF))
 152     return false;
 153
 154   const TargetRegisterInfo *RegInfo = MF.getSubtarget().getRegisterInfo();
 155   return RegInfo->useFPForScavengingIndex(MF) &&
 156          !RegInfo->hasStackRealignment(MF);
 157 }
 158
 159 bool TargetFrameLowering::isSafeForNoCSROpt(const Function &F) {
 160   if (!F.hasLocalLinkage() || F.hasAddressTaken() ||
 161       !F.hasFnAttribute(Attribute::NoRecurse))
 162     return false;
 163   // Function should not be optimized as tail call.
 164   for (const User *U : F.users())
 165     if (auto *CB = dyn_cast<CallBase>(U))
 166       if (CB->isTailCall())
 167         return false;
 168   return true;
 169 }
 170
 171 int TargetFrameLowering::getInitialCFAOffset(const MachineFunction &MF) const {
 172   llvm_unreachable("getInitialCFAOffset() not implemented!");
 173 }
 174
 175 Register
 176 TargetFrameLowering::getInitialCFARegister(const MachineFunction &MF) const {
 177   llvm_unreachable("getInitialCFARegister() not implemented!");
 178 }
 179
 180 TargetFrameLowering::DwarfFrameBase
 181 TargetFrameLowering::getDwarfFrameBase(const MachineFunction &MF) const {
 182   const TargetRegisterInfo *RI = MF.getSubtarget().getRegisterInfo();
 183   return DwarfFrameBase{DwarfFrameBase::Register, {RI->getFrameRegister(MF)}};
 184 }