1 //===-- MachineFrameInfo.cpp ---------------------------------------------===//
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 /// \file Implements MachineFrameInfo that manages the stack frame.
11 //
12 //===----------------------------------------------------------------------===//
13 
14 #include "llvm/CodeGen/MachineFrameInfo.h"
15 
16 #include "llvm/ADT/BitVector.h"
17 #include "llvm/CodeGen/MachineFunction.h"
18 #include "llvm/CodeGen/MachineRegisterInfo.h"
19 #include "llvm/Support/Debug.h"
20 #include "llvm/Support/raw_ostream.h"
21 #include "llvm/Target/TargetFrameLowering.h"
22 #include "llvm/Target/TargetInstrInfo.h"
23 #include "llvm/Target/TargetRegisterInfo.h"
24 #include "llvm/Target/TargetSubtargetInfo.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   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 isSS, const AllocaInst *Alloca) {
51   assert(Size != 0 && "Cannot allocate zero size stack objects!");
52   Alignment = clampStackAlignment(!StackRealignable, Alignment, StackAlignment);
53   Objects.push_back(StackObject(Size, Alignment, 0, false, isSS, Alloca,
54                                 !isSS));
55   int Index = (int)Objects.size() - NumFixedObjects - 1;
56   assert(Index >= 0 && "Bad frame index!");
57   ensureMaxAlignment(Alignment);
58   return Index;
59 }
60 
61 int MachineFrameInfo::CreateSpillStackObject(uint64_t Size,
62                                              unsigned Alignment) {
63   Alignment = clampStackAlignment(!StackRealignable, Alignment, StackAlignment);
64   CreateStackObject(Size, Alignment, true);
65   int Index = (int)Objects.size() - NumFixedObjects - 1;
66   ensureMaxAlignment(Alignment);
67   return Index;
68 }
69 
70 int MachineFrameInfo::CreateVariableSizedObject(unsigned Alignment,
71                                                 const AllocaInst *Alloca) {
72   HasVarSizedObjects = true;
73   Alignment = clampStackAlignment(!StackRealignable, Alignment, StackAlignment);
74   Objects.push_back(StackObject(0, Alignment, 0, false, false, Alloca, true));
75   ensureMaxAlignment(Alignment);
76   return (int)Objects.size()-NumFixedObjects-1;
77 }
78 
79 int MachineFrameInfo::CreateFixedObject(uint64_t Size, int64_t SPOffset,
80                                         bool Immutable, bool isAliased) {
81   assert(Size != 0 && "Cannot allocate zero size fixed stack objects!");
82   // The alignment of the frame index can be determined from its offset from
83   // the incoming frame position.  If the frame object is at offset 32 and
84   // the stack is guaranteed to be 16-byte aligned, then we know that the
85   // object is 16-byte aligned. Note that unlike the non-fixed case, if the
86   // stack needs realignment, we can't assume that the stack will in fact be
87   // aligned.
88   unsigned Align = MinAlign(SPOffset, ForcedRealign ? 1 : StackAlignment);
89   Align = clampStackAlignment(!StackRealignable, Align, StackAlignment);
90   Objects.insert(Objects.begin(), StackObject(Size, Align, SPOffset, Immutable,
91                                               /*isSS*/   false,
92                                               /*Alloca*/ nullptr, isAliased));
93   return -++NumFixedObjects;
94 }
95 
96 int MachineFrameInfo::CreateFixedSpillStackObject(uint64_t Size,
97                                                   int64_t SPOffset,
98                                                   bool Immutable) {
99   unsigned Align = MinAlign(SPOffset, ForcedRealign ? 1 : StackAlignment);
100   Align = clampStackAlignment(!StackRealignable, Align, StackAlignment);
101   Objects.insert(Objects.begin(), StackObject(Size, Align, SPOffset, Immutable,
102                                               /*isSS*/ true,
103                                               /*Alloca*/ nullptr,
104                                               /*isAliased*/ false));
105   return -++NumFixedObjects;
106 }
107 
108 BitVector MachineFrameInfo::getPristineRegs(const MachineFunction &MF) const {
109   const TargetRegisterInfo *TRI = MF.getSubtarget().getRegisterInfo();
110   BitVector BV(TRI->getNumRegs());
111 
112   // Before CSI is calculated, no registers are considered pristine. They can be
113   // freely used and PEI will make sure they are saved.
114   if (!isCalleeSavedInfoValid())
115     return BV;
116 
117   const MachineRegisterInfo &MRI = MF.getRegInfo();
118   for (const MCPhysReg *CSR = MRI.getCalleeSavedRegs(); CSR && *CSR;
119        ++CSR)
120     BV.set(*CSR);
121 
122   // Saved CSRs are not pristine.
123   for (auto &I : getCalleeSavedInfo())
124     for (MCSubRegIterator S(I.getReg(), TRI, true); S.isValid(); ++S)
125       BV.reset(*S);
126 
127   return BV;
128 }
129 
130 unsigned MachineFrameInfo::estimateStackSize(const MachineFunction &MF) const {
131   const TargetFrameLowering *TFI = MF.getSubtarget().getFrameLowering();
132   const TargetRegisterInfo *RegInfo = MF.getSubtarget().getRegisterInfo();
133   unsigned MaxAlign = getMaxAlignment();
134   int Offset = 0;
135 
136   // This code is very, very similar to PEI::calculateFrameObjectOffsets().
137   // It really should be refactored to share code. Until then, changes
138   // should keep in mind that there's tight coupling between the two.
139 
140   for (int i = getObjectIndexBegin(); i != 0; ++i) {
141     int FixedOff = -getObjectOffset(i);
142     if (FixedOff > Offset) Offset = FixedOff;
143   }
144   for (unsigned i = 0, e = getObjectIndexEnd(); i != e; ++i) {
145     if (isDeadObjectIndex(i))
146       continue;
147     Offset += getObjectSize(i);
148     unsigned Align = getObjectAlignment(i);
149     // Adjust to alignment boundary
150     Offset = (Offset+Align-1)/Align*Align;
151 
152     MaxAlign = std::max(Align, MaxAlign);
153   }
154 
155   if (adjustsStack() && TFI->hasReservedCallFrame(MF))
156     Offset += getMaxCallFrameSize();
157 
158   // Round up the size to a multiple of the alignment.  If the function has
159   // any calls or alloca's, align to the target's StackAlignment value to
160   // ensure that the callee's frame or the alloca data is suitably aligned;
161   // otherwise, for leaf functions, align to the TransientStackAlignment
162   // value.
163   unsigned StackAlign;
164   if (adjustsStack() || hasVarSizedObjects() ||
165       (RegInfo->needsStackRealignment(MF) && getObjectIndexEnd() != 0))
166     StackAlign = TFI->getStackAlignment();
167   else
168     StackAlign = TFI->getTransientStackAlignment();
169 
170   // If the frame pointer is eliminated, all frame offsets will be relative to
171   // SP not FP. Align to MaxAlign so this works.
172   StackAlign = std::max(StackAlign, MaxAlign);
173   unsigned AlignMask = StackAlign - 1;
174   Offset = (Offset + AlignMask) & ~uint64_t(AlignMask);
175 
176   return (unsigned)Offset;
177 }
178 
179 void MachineFrameInfo::computeMaxCallFrameSize(const MachineFunction &MF) {
180   const TargetInstrInfo &TII = *MF.getSubtarget().getInstrInfo();
181   unsigned FrameSetupOpcode = TII.getCallFrameSetupOpcode();
182   unsigned FrameDestroyOpcode = TII.getCallFrameDestroyOpcode();
183   assert(FrameSetupOpcode != ~0u && FrameDestroyOpcode != ~0u &&
184          "Can only compute MaxCallFrameSize if Setup/Destroy opcode are known");
185 
186   MaxCallFrameSize = 0;
187   for (const MachineBasicBlock &MBB : MF) {
188     for (const MachineInstr &MI : MBB) {
189       unsigned Opcode = MI.getOpcode();
190       if (Opcode == FrameSetupOpcode || Opcode == FrameDestroyOpcode) {
191         unsigned Size = TII.getFrameSize(MI);
192         MaxCallFrameSize = std::max(MaxCallFrameSize, Size);
193         AdjustsStack = true;
194       } else if (MI.isInlineAsm()) {
195         // Some inline asm's need a stack frame, as indicated by operand 1.
196         unsigned ExtraInfo = MI.getOperand(InlineAsm::MIOp_ExtraInfo).getImm();
197         if (ExtraInfo & InlineAsm::Extra_IsAlignStack)
198           AdjustsStack = true;
199       }
200     }
201   }
202 }
203 
204 void MachineFrameInfo::print(const MachineFunction &MF, raw_ostream &OS) const{
205   if (Objects.empty()) return;
206 
207   const TargetFrameLowering *FI = MF.getSubtarget().getFrameLowering();
208   int ValOffset = (FI ? FI->getOffsetOfLocalArea() : 0);
209 
210   OS << "Frame Objects:\n";
211 
212   for (unsigned i = 0, e = Objects.size(); i != e; ++i) {
213     const StackObject &SO = Objects[i];
214     OS << "  fi#" << (int)(i-NumFixedObjects) << ": ";
215     if (SO.Size == ~0ULL) {
216       OS << "dead\n";
217       continue;
218     }
219     if (SO.Size == 0)
220       OS << "variable sized";
221     else
222       OS << "size=" << SO.Size;
223     OS << ", align=" << SO.Alignment;
224 
225     if (i < NumFixedObjects)
226       OS << ", fixed";
227     if (i < NumFixedObjects || SO.SPOffset != -1) {
228       int64_t Off = SO.SPOffset - ValOffset;
229       OS << ", at location [SP";
230       if (Off > 0)
231         OS << "+" << Off;
232       else if (Off < 0)
233         OS << Off;
234       OS << "]";
235     }
236     OS << "\n";
237   }
238 }
239 
240 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
241 LLVM_DUMP_METHOD void MachineFrameInfo::dump(const MachineFunction &MF) const {
242   print(MF, dbgs());
243 }
244 #endif
245