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(Align Alignment) {
  32   if (!StackRealignable)
  33     assert(Alignment <= StackAlignment &&
  34            "For targets without stack realignment, Alignment is out of limit!");
  35   if (MaxAlignment < Alignment)
  36     MaxAlignment = Alignment;
  37 }
  38
  39 /// Clamp the alignment if requested and emit a warning.
  40 static inline Align clampStackAlignment(bool ShouldClamp, Align Alignment,
  41                                         Align StackAlignment) {
  42   if (!ShouldClamp || Alignment <= StackAlignment)
  43     return Alignment;
  44   LLVM_DEBUG(dbgs() << "Warning: requested alignment " << Alignment.value()
  45                     << " exceeds the stack alignment " << StackAlignment.value()
  46                     << " when stack realignment is off" << '\n');
  47   return StackAlignment;
  48 }
  49
  50 int MachineFrameInfo::CreateStackObject(uint64_t Size, Align Alignment,
  51                                         bool IsSpillSlot,
  52                                         const AllocaInst *Alloca,
  53                                         uint8_t StackID) {
  54   assert(Size != 0 && "Cannot allocate zero size stack objects!");
  55   Alignment = clampStackAlignment(!StackRealignable, Alignment, StackAlignment);
  56   Objects.push_back(StackObject(Size, Alignment, 0, false, IsSpillSlot, Alloca,
  57                                 !IsSpillSlot, StackID));
  58   int Index = (int)Objects.size() - NumFixedObjects - 1;
  59   assert(Index >= 0 && "Bad frame index!");
  60   if (StackID == 0)
  61     ensureMaxAlignment(Alignment);
  62   return Index;
  63 }
  64
  65 int MachineFrameInfo::CreateSpillStackObject(uint64_t Size, Align 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(Align 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   Align Alignment =
  92       commonAlignment(ForcedRealign ? Align::None() : StackAlignment, SPOffset);
  93   Alignment = clampStackAlignment(!StackRealignable, Alignment, StackAlignment);
  94   Objects.insert(Objects.begin(),
  95                  StackObject(Size, Alignment, SPOffset, IsImmutable,
  96                              /*IsSpillSlot=*/false, /*Alloca=*/nullptr,
  97                              IsAliased));
  98   return -++NumFixedObjects;
  99 }
 100
 101 int MachineFrameInfo::CreateFixedSpillStackObject(uint64_t Size,
 102                                                   int64_t SPOffset,
 103                                                   bool IsImmutable) {
 104   Align Alignment =
 105       commonAlignment(ForcedRealign ? Align::None() : StackAlignment, SPOffset);
 106   Alignment = clampStackAlignment(!StackRealignable, Alignment, StackAlignment);
 107   Objects.insert(Objects.begin(),
 108                  StackObject(Size, Alignment, SPOffset, IsImmutable,
 109                              /*IsSpillSlot=*/true, /*Alloca=*/nullptr,
 110                              /*IsAliased=*/false));
 111   return -++NumFixedObjects;
 112 }
 113
 114 BitVector MachineFrameInfo::getPristineRegs(const MachineFunction &MF) const {
 115   const TargetRegisterInfo *TRI = MF.getSubtarget().getRegisterInfo();
 116   BitVector BV(TRI->getNumRegs());
 117
 118   // Before CSI is calculated, no registers are considered pristine. They can be
 119   // freely used and PEI will make sure they are saved.
 120   if (!isCalleeSavedInfoValid())
 121     return BV;
 122
 123   const MachineRegisterInfo &MRI = MF.getRegInfo();
 124   for (const MCPhysReg *CSR = MRI.getCalleeSavedRegs(); CSR && *CSR;
 125        ++CSR)
 126     BV.set(*CSR);
 127
 128   // Saved CSRs are not pristine.
 129   for (auto &I : getCalleeSavedInfo())
 130     for (MCSubRegIterator S(I.getReg(), TRI, true); S.isValid(); ++S)
 131       BV.reset(*S);
 132
 133   return BV;
 134 }
 135
 136 unsigned MachineFrameInfo::estimateStackSize(const MachineFunction &MF) const {
 137   const TargetFrameLowering *TFI = MF.getSubtarget().getFrameLowering();
 138   const TargetRegisterInfo *RegInfo = MF.getSubtarget().getRegisterInfo();
 139   unsigned MaxAlign = getMaxAlignment();
 140   int Offset = 0;
 141
 142   // This code is very, very similar to PEI::calculateFrameObjectOffsets().
 143   // It really should be refactored to share code. Until then, changes
 144   // should keep in mind that there's tight coupling between the two.
 145
 146   for (int i = getObjectIndexBegin(); i != 0; ++i) {
 147     // Only estimate stack size of default stack.
 148     if (getStackID(i) != TargetStackID::Default)
 149       continue;
 150     int FixedOff = -getObjectOffset(i);
 151     if (FixedOff > Offset) Offset = FixedOff;
 152   }
 153   for (unsigned i = 0, e = getObjectIndexEnd(); i != e; ++i) {
 154     // Only estimate stack size of live objects on default stack.
 155     if (isDeadObjectIndex(i) || getStackID(i) != TargetStackID::Default)
 156       continue;
 157     Offset += getObjectSize(i);
 158     unsigned Align = getObjectAlignment(i);
 159     // Adjust to alignment boundary
 160     Offset = (Offset+Align-1)/Align*Align;
 161
 162     MaxAlign = std::max(Align, MaxAlign);
 163   }
 164
 165   if (adjustsStack() && TFI->hasReservedCallFrame(MF))
 166     Offset += getMaxCallFrameSize();
 167
 168   // Round up the size to a multiple of the alignment.  If the function has
 169   // any calls or alloca's, align to the target's StackAlignment value to
 170   // ensure that the callee's frame or the alloca data is suitably aligned;
 171   // otherwise, for leaf functions, align to the TransientStackAlignment
 172   // value.
 173   unsigned StackAlign;
 174   if (adjustsStack() || hasVarSizedObjects() ||
 175       (RegInfo->needsStackRealignment(MF) && getObjectIndexEnd() != 0))
 176     StackAlign = TFI->getStackAlignment();
 177   else
 178     StackAlign = TFI->getTransientStackAlignment();
 179
 180   // If the frame pointer is eliminated, all frame offsets will be relative to
 181   // SP not FP. Align to MaxAlign so this works.
 182   StackAlign = std::max(StackAlign, MaxAlign);
 183   unsigned AlignMask = StackAlign - 1;
 184   Offset = (Offset + AlignMask) & ~uint64_t(AlignMask);
 185
 186   return (unsigned)Offset;
 187 }
 188
 189 void MachineFrameInfo::computeMaxCallFrameSize(const MachineFunction &MF) {
 190   const TargetInstrInfo &TII = *MF.getSubtarget().getInstrInfo();
 191   unsigned FrameSetupOpcode = TII.getCallFrameSetupOpcode();
 192   unsigned FrameDestroyOpcode = TII.getCallFrameDestroyOpcode();
 193   assert(FrameSetupOpcode != ~0u && FrameDestroyOpcode != ~0u &&
 194          "Can only compute MaxCallFrameSize if Setup/Destroy opcode are known");
 195
 196   MaxCallFrameSize = 0;
 197   for (const MachineBasicBlock &MBB : MF) {
 198     for (const MachineInstr &MI : MBB) {
 199       unsigned Opcode = MI.getOpcode();
 200       if (Opcode == FrameSetupOpcode || Opcode == FrameDestroyOpcode) {
 201         unsigned Size = TII.getFrameSize(MI);
 202         MaxCallFrameSize = std::max(MaxCallFrameSize, Size);
 203         AdjustsStack = true;
 204       } else if (MI.isInlineAsm()) {
 205         // Some inline asm's need a stack frame, as indicated by operand 1.
 206         unsigned ExtraInfo = MI.getOperand(InlineAsm::MIOp_ExtraInfo).getImm();
 207         if (ExtraInfo & InlineAsm::Extra_IsAlignStack)
 208           AdjustsStack = true;
 209       }
 210     }
 211   }
 212 }
 213
 214 void MachineFrameInfo::print(const MachineFunction &MF, raw_ostream &OS) const{
 215   if (Objects.empty()) return;
 216
 217   const TargetFrameLowering *FI = MF.getSubtarget().getFrameLowering();
 218   int ValOffset = (FI ? FI->getOffsetOfLocalArea() : 0);
 219
 220   OS << "Frame Objects:\n";
 221
 222   for (unsigned i = 0, e = Objects.size(); i != e; ++i) {
 223     const StackObject &SO = Objects[i];
 224     OS << "  fi#" << (int)(i-NumFixedObjects) << ": ";
 225
 226     if (SO.StackID != 0)
 227       OS << "id=" << static_cast<unsigned>(SO.StackID) << ' ';
 228
 229     if (SO.Size == ~0ULL) {
 230       OS << "dead\n";
 231       continue;
 232     }
 233     if (SO.Size == 0)
 234       OS << "variable sized";
 235     else
 236       OS << "size=" << SO.Size;
 237     OS << ", align=" << SO.Alignment.value();
 238
 239     if (i < NumFixedObjects)
 240       OS << ", fixed";
 241     if (i < NumFixedObjects || SO.SPOffset != -1) {
 242       int64_t Off = SO.SPOffset - ValOffset;
 243       OS << ", at location [SP";
 244       if (Off > 0)
 245         OS << "+" << Off;
 246       else if (Off < 0)
 247         OS << Off;
 248       OS << "]";
 249     }
 250     OS << "\n";
 251   }
 252 }
 253
 254 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
 255 LLVM_DUMP_METHOD void MachineFrameInfo::dump(const MachineFunction &MF) const {
 256   print(MF, dbgs());
 257 }
 258 #endif