lib/CodeGen/MachineFrameInfo.cpp

   1 //===-- MachineFrameInfo.cpp ---------------------------------------------===//
   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 Implements MachineFrameInfo that manages the stack frame.
  10 //
  11 //===----------------------------------------------------------------------===//
  12
  13 #include "llvm/CodeGen/MachineFrameInfo.h"
  14
  15 #include "llvm/ADT/BitVector.h"
  16 #include "llvm/CodeGen/MachineFunction.h"
  17 #include "llvm/CodeGen/MachineRegisterInfo.h"
  18 #include "llvm/CodeGen/TargetFrameLowering.h"
  19 #include "llvm/CodeGen/TargetInstrInfo.h"
  20 #include "llvm/CodeGen/TargetRegisterInfo.h"
  21 #include "llvm/CodeGen/TargetSubtargetInfo.h"
  22 #include "llvm/Config/llvm-config.h"
  23 #include "llvm/Support/Debug.h"
  24 #include "llvm/Support/raw_ostream.h"
  25 #include <cassert>
  26
  27 #define DEBUG_TYPE "codegen"
  28
  29 using namespace llvm;
  30
  31 void MachineFrameInfo::ensureMaxAlignment(unsigned Align) {
  32   if (!StackRealignable)
  33     assert(Align <= StackAlignment &&
  34            "For targets without stack realignment, Align is out of limit!");
  35   if (MaxAlignment < Align) MaxAlignment = Align;
  36 }
  37
  38 /// Clamp the alignment if requested and emit a warning.
  39 static inline unsigned clampStackAlignment(bool ShouldClamp, unsigned Align,
  40                                            unsigned StackAlign) {
  41   if (!ShouldClamp || Align <= StackAlign)
  42     return Align;
  43   LLVM_DEBUG(dbgs() << "Warning: requested alignment " << Align
  44                     << " exceeds the stack alignment " << StackAlign
  45                     << " when stack realignment is off" << '\n');
  46   return StackAlign;
  47 }
  48
  49 int MachineFrameInfo::CreateStackObject(uint64_t Size, unsigned Alignment,
  50                                         bool IsSpillSlot,
  51                                         const AllocaInst *Alloca,
  52                                         uint8_t StackID) {
  53   assert(Size != 0 && "Cannot allocate zero size stack objects!");
  54   Alignment = clampStackAlignment(!StackRealignable, Alignment, StackAlignment);
  55   Objects.push_back(StackObject(Size, Alignment, 0, false, IsSpillSlot, Alloca,
  56                                 !IsSpillSlot, StackID));
  57   int Index = (int)Objects.size() - NumFixedObjects - 1;
  58   assert(Index >= 0 && "Bad frame index!");
  59   if (StackID == 0)
  60     ensureMaxAlignment(Alignment);
  61   return Index;
  62 }
  63
  64 int MachineFrameInfo::CreateSpillStackObject(uint64_t Size,
  65                                              unsigned Alignment) {
  66   Alignment = clampStackAlignment(!StackRealignable, Alignment, StackAlignment);
  67   CreateStackObject(Size, Alignment, true);
  68   int Index = (int)Objects.size() - NumFixedObjects - 1;
  69   ensureMaxAlignment(Alignment);
  70   return Index;
  71 }
  72
  73 int MachineFrameInfo::CreateVariableSizedObject(unsigned Alignment,
  74                                                 const AllocaInst *Alloca) {
  75   HasVarSizedObjects = true;
  76   Alignment = clampStackAlignment(!StackRealignable, Alignment, StackAlignment);
  77   Objects.push_back(StackObject(0, Alignment, 0, false, false, Alloca, true));
  78   ensureMaxAlignment(Alignment);
  79   return (int)Objects.size()-NumFixedObjects-1;
  80 }
  81
  82 int MachineFrameInfo::CreateFixedObject(uint64_t Size, int64_t SPOffset,
  83                                         bool IsImmutable, bool IsAliased) {
  84   assert(Size != 0 && "Cannot allocate zero size fixed stack objects!");
  85   // The alignment of the frame index can be determined from its offset from
  86   // the incoming frame position.  If the frame object is at offset 32 and
  87   // the stack is guaranteed to be 16-byte aligned, then we know that the
  88   // object is 16-byte aligned. Note that unlike the non-fixed case, if the
  89   // stack needs realignment, we can't assume that the stack will in fact be
  90   // aligned.
  91   unsigned Alignment = MinAlign(SPOffset, ForcedRealign ? 1 : StackAlignment);
  92   Alignment = clampStackAlignment(!StackRealignable, Alignment, StackAlignment);
  93   Objects.insert(Objects.begin(),
  94                  StackObject(Size, Alignment, SPOffset, IsImmutable,
  95                              /*IsSpillSlot=*/false, /*Alloca=*/nullptr,
  96                              IsAliased));
  97   return -++NumFixedObjects;
  98 }
  99
 100 int MachineFrameInfo::CreateFixedSpillStackObject(uint64_t Size,
 101                                                   int64_t SPOffset,
 102                                                   bool IsImmutable) {
 103   unsigned Alignment = MinAlign(SPOffset, ForcedRealign ? 1 : StackAlignment);
 104   Alignment = clampStackAlignment(!StackRealignable, Alignment, StackAlignment);
 105   Objects.insert(Objects.begin(),
 106                  StackObject(Size, Alignment, SPOffset, IsImmutable,
 107                              /*IsSpillSlot=*/true, /*Alloca=*/nullptr,
 108                              /*IsAliased=*/false));
 109   return -++NumFixedObjects;
 110 }
 111
 112 BitVector MachineFrameInfo::getPristineRegs(const MachineFunction &MF) const {
 113   const TargetRegisterInfo *TRI = MF.getSubtarget().getRegisterInfo();
 114   BitVector BV(TRI->getNumRegs());
 115
 116   // Before CSI is calculated, no registers are considered pristine. They can be
 117   // freely used and PEI will make sure they are saved.
 118   if (!isCalleeSavedInfoValid())
 119     return BV;
 120
 121   const MachineRegisterInfo &MRI = MF.getRegInfo();
 122   for (const MCPhysReg *CSR = MRI.getCalleeSavedRegs(); CSR && *CSR;
 123        ++CSR)
 124     BV.set(*CSR);
 125
 126   // Saved CSRs are not pristine.
 127   for (auto &I : getCalleeSavedInfo())
 128     for (MCSubRegIterator S(I.getReg(), TRI, true); S.isValid(); ++S)
 129       BV.reset(*S);
 130
 131   return BV;
 132 }
 133
 134 unsigned MachineFrameInfo::estimateStackSize(const MachineFunction &MF) const {
 135   const TargetFrameLowering *TFI = MF.getSubtarget().getFrameLowering();
 136   const TargetRegisterInfo *RegInfo = MF.getSubtarget().getRegisterInfo();
 137   unsigned MaxAlign = getMaxAlignment();
 138   int Offset = 0;
 139
 140   // This code is very, very similar to PEI::calculateFrameObjectOffsets().
 141   // It really should be refactored to share code. Until then, changes
 142   // should keep in mind that there's tight coupling between the two.
 143
 144   for (int i = getObjectIndexBegin(); i != 0; ++i) {
 145     // Only estimate stack size of default stack.
 146     if (getStackID(i) != TargetStackID::Default)
 147       continue;
 148     int FixedOff = -getObjectOffset(i);
 149     if (FixedOff > Offset) Offset = FixedOff;
 150   }
 151   for (unsigned i = 0, e = getObjectIndexEnd(); i != e; ++i) {
 152     // Only estimate stack size of live objects on default stack.
 153     if (isDeadObjectIndex(i) || getStackID(i) != TargetStackID::Default)
 154       continue;
 155     Offset += getObjectSize(i);
 156     unsigned Align = getObjectAlignment(i);
 157     // Adjust to alignment boundary
 158     Offset = (Offset+Align-1)/Align*Align;
 159
 160     MaxAlign = std::max(Align, MaxAlign);
 161   }
 162
 163   if (adjustsStack() && TFI->hasReservedCallFrame(MF))
 164     Offset += getMaxCallFrameSize();
 165
 166   // Round up the size to a multiple of the alignment.  If the function has
 167   // any calls or alloca's, align to the target's StackAlignment value to
 168   // ensure that the callee's frame or the alloca data is suitably aligned;
 169   // otherwise, for leaf functions, align to the TransientStackAlignment
 170   // value.
 171   unsigned StackAlign;
 172   if (adjustsStack() || hasVarSizedObjects() ||
 173       (RegInfo->needsStackRealignment(MF) && getObjectIndexEnd() != 0))
 174     StackAlign = TFI->getStackAlignment();
 175   else
 176     StackAlign = TFI->getTransientStackAlignment();
 177
 178   // If the frame pointer is eliminated, all frame offsets will be relative to
 179   // SP not FP. Align to MaxAlign so this works.
 180   StackAlign = std::max(StackAlign, MaxAlign);
 181   unsigned AlignMask = StackAlign - 1;
 182   Offset = (Offset + AlignMask) & ~uint64_t(AlignMask);
 183
 184   return (unsigned)Offset;
 185 }
 186
 187 void MachineFrameInfo::computeMaxCallFrameSize(const MachineFunction &MF) {
 188   const TargetInstrInfo &TII = *MF.getSubtarget().getInstrInfo();
 189   unsigned FrameSetupOpcode = TII.getCallFrameSetupOpcode();
 190   unsigned FrameDestroyOpcode = TII.getCallFrameDestroyOpcode();
 191   assert(FrameSetupOpcode != ~0u && FrameDestroyOpcode != ~0u &&
 192          "Can only compute MaxCallFrameSize if Setup/Destroy opcode are known");
 193
 194   MaxCallFrameSize = 0;
 195   for (const MachineBasicBlock &MBB : MF) {
 196     for (const MachineInstr &MI : MBB) {
 197       unsigned Opcode = MI.getOpcode();
 198       if (Opcode == FrameSetupOpcode || Opcode == FrameDestroyOpcode) {
 199         unsigned Size = TII.getFrameSize(MI);
 200         MaxCallFrameSize = std::max(MaxCallFrameSize, Size);
 201         AdjustsStack = true;
 202       } else if (MI.isInlineAsm()) {
 203         // Some inline asm's need a stack frame, as indicated by operand 1.
 204         unsigned ExtraInfo = MI.getOperand(InlineAsm::MIOp_ExtraInfo).getImm();
 205         if (ExtraInfo & InlineAsm::Extra_IsAlignStack)
 206           AdjustsStack = true;
 207       }
 208     }
 209   }
 210 }
 211
 212 void MachineFrameInfo::print(const MachineFunction &MF, raw_ostream &OS) const{
 213   if (Objects.empty()) return;
 214
 215   const TargetFrameLowering *FI = MF.getSubtarget().getFrameLowering();
 216   int ValOffset = (FI ? FI->getOffsetOfLocalArea() : 0);
 217
 218   OS << "Frame Objects:\n";
 219
 220   for (unsigned i = 0, e = Objects.size(); i != e; ++i) {
 221     const StackObject &SO = Objects[i];
 222     OS << "  fi#" << (int)(i-NumFixedObjects) << ": ";
 223
 224     if (SO.StackID != 0)
 225       OS << "id=" << static_cast<unsigned>(SO.StackID) << ' ';
 226
 227     if (SO.Size == ~0ULL) {
 228       OS << "dead\n";
 229       continue;
 230     }
 231     if (SO.Size == 0)
 232       OS << "variable sized";
 233     else
 234       OS << "size=" << SO.Size;
 235     OS << ", align=" << SO.Alignment;
 236
 237     if (i < NumFixedObjects)
 238       OS << ", fixed";
 239     if (i < NumFixedObjects || SO.SPOffset != -1) {
 240       int64_t Off = SO.SPOffset - ValOffset;
 241       OS << ", at location [SP";
 242       if (Off > 0)
 243         OS << "+" << Off;
 244       else if (Off < 0)
 245         OS << Off;
 246       OS << "]";
 247     }
 248     OS << "\n";
 249   }
 250 }
 251
 252 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
 253 LLVM_DUMP_METHOD void MachineFrameInfo::dump(const MachineFunction &MF) const {
 254   print(MF, dbgs());
 255 }
 256 #endif