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                                         uint8_t ID) {
52   assert(Size != 0 && "Cannot allocate zero size stack objects!");
53   Alignment = clampStackAlignment(!StackRealignable, Alignment, StackAlignment);
54   Objects.push_back(StackObject(Size, Alignment, 0, false, isSS, Alloca,
55                                 !isSS, ID));
56   int Index = (int)Objects.size() - NumFixedObjects - 1;
57   assert(Index >= 0 && "Bad frame index!");
58   ensureMaxAlignment(Alignment);
59   return Index;
60 }
61 
62 int MachineFrameInfo::CreateSpillStackObject(uint64_t Size,
63                                              unsigned Alignment) {
64   Alignment = clampStackAlignment(!StackRealignable, Alignment, StackAlignment);
65   CreateStackObject(Size, Alignment, true);
66   int Index = (int)Objects.size() - NumFixedObjects - 1;
67   ensureMaxAlignment(Alignment);
68   return Index;
69 }
70 
71 int MachineFrameInfo::CreateVariableSizedObject(unsigned Alignment,
72                                                 const AllocaInst *Alloca) {
73   HasVarSizedObjects = true;
74   Alignment = clampStackAlignment(!StackRealignable, Alignment, StackAlignment);
75   Objects.push_back(StackObject(0, Alignment, 0, false, false, Alloca, true));
76   ensureMaxAlignment(Alignment);
77   return (int)Objects.size()-NumFixedObjects-1;
78 }
79 
80 int MachineFrameInfo::CreateFixedObject(uint64_t Size, int64_t SPOffset,
81                                         bool Immutable, bool isAliased) {
82   assert(Size != 0 && "Cannot allocate zero size fixed stack objects!");
83   // The alignment of the frame index can be determined from its offset from
84   // the incoming frame position.  If the frame object is at offset 32 and
85   // the stack is guaranteed to be 16-byte aligned, then we know that the
86   // object is 16-byte aligned. Note that unlike the non-fixed case, if the
87   // stack needs realignment, we can't assume that the stack will in fact be
88   // aligned.
89   unsigned Align = MinAlign(SPOffset, ForcedRealign ? 1 : StackAlignment);
90   Align = clampStackAlignment(!StackRealignable, Align, StackAlignment);
91   Objects.insert(Objects.begin(), StackObject(Size, Align, SPOffset, Immutable,
92                                               /*isSS*/   false,
93                                               /*Alloca*/ nullptr, isAliased));
94   return -++NumFixedObjects;
95 }
96 
97 int MachineFrameInfo::CreateFixedSpillStackObject(uint64_t Size,
98                                                   int64_t SPOffset,
99                                                   bool Immutable) {
100   unsigned Align = MinAlign(SPOffset, ForcedRealign ? 1 : StackAlignment);
101   Align = clampStackAlignment(!StackRealignable, Align, StackAlignment);
102   Objects.insert(Objects.begin(), StackObject(Size, Align, SPOffset, Immutable,
103                                               /*isSS*/ true,
104                                               /*Alloca*/ nullptr,
105                                               /*isAliased*/ false));
106   return -++NumFixedObjects;
107 }
108 
109 BitVector MachineFrameInfo::getPristineRegs(const MachineFunction &MF) const {
110   const TargetRegisterInfo *TRI = MF.getSubtarget().getRegisterInfo();
111   BitVector BV(TRI->getNumRegs());
112 
113   // Before CSI is calculated, no registers are considered pristine. They can be
114   // freely used and PEI will make sure they are saved.
115   if (!isCalleeSavedInfoValid())
116     return BV;
117 
118   const MachineRegisterInfo &MRI = MF.getRegInfo();
119   for (const MCPhysReg *CSR = MRI.getCalleeSavedRegs(); CSR && *CSR;
120        ++CSR)
121     BV.set(*CSR);
122 
123   // Saved CSRs are not pristine.
124   for (auto &I : getCalleeSavedInfo())
125     for (MCSubRegIterator S(I.getReg(), TRI, true); S.isValid(); ++S)
126       BV.reset(*S);
127 
128   return BV;
129 }
130 
131 unsigned MachineFrameInfo::estimateStackSize(const MachineFunction &MF) const {
132   const TargetFrameLowering *TFI = MF.getSubtarget().getFrameLowering();
133   const TargetRegisterInfo *RegInfo = MF.getSubtarget().getRegisterInfo();
134   unsigned MaxAlign = getMaxAlignment();
135   int Offset = 0;
136 
137   // This code is very, very similar to PEI::calculateFrameObjectOffsets().
138   // It really should be refactored to share code. Until then, changes
139   // should keep in mind that there's tight coupling between the two.
140 
141   for (int i = getObjectIndexBegin(); i != 0; ++i) {
142     int FixedOff = -getObjectOffset(i);
143     if (FixedOff > Offset) Offset = FixedOff;
144   }
145   for (unsigned i = 0, e = getObjectIndexEnd(); i != e; ++i) {
146     if (isDeadObjectIndex(i))
147       continue;
148     Offset += getObjectSize(i);
149     unsigned Align = getObjectAlignment(i);
150     // Adjust to alignment boundary
151     Offset = (Offset+Align-1)/Align*Align;
152 
153     MaxAlign = std::max(Align, MaxAlign);
154   }
155 
156   if (adjustsStack() && TFI->hasReservedCallFrame(MF))
157     Offset += getMaxCallFrameSize();
158 
159   // Round up the size to a multiple of the alignment.  If the function has
160   // any calls or alloca's, align to the target's StackAlignment value to
161   // ensure that the callee's frame or the alloca data is suitably aligned;
162   // otherwise, for leaf functions, align to the TransientStackAlignment
163   // value.
164   unsigned StackAlign;
165   if (adjustsStack() || hasVarSizedObjects() ||
166       (RegInfo->needsStackRealignment(MF) && getObjectIndexEnd() != 0))
167     StackAlign = TFI->getStackAlignment();
168   else
169     StackAlign = TFI->getTransientStackAlignment();
170 
171   // If the frame pointer is eliminated, all frame offsets will be relative to
172   // SP not FP. Align to MaxAlign so this works.
173   StackAlign = std::max(StackAlign, MaxAlign);
174   unsigned AlignMask = StackAlign - 1;
175   Offset = (Offset + AlignMask) & ~uint64_t(AlignMask);
176 
177   return (unsigned)Offset;
178 }
179 
180 void MachineFrameInfo::computeMaxCallFrameSize(const MachineFunction &MF) {
181   const TargetInstrInfo &TII = *MF.getSubtarget().getInstrInfo();
182   unsigned FrameSetupOpcode = TII.getCallFrameSetupOpcode();
183   unsigned FrameDestroyOpcode = TII.getCallFrameDestroyOpcode();
184   assert(FrameSetupOpcode != ~0u && FrameDestroyOpcode != ~0u &&
185          "Can only compute MaxCallFrameSize if Setup/Destroy opcode are known");
186 
187   MaxCallFrameSize = 0;
188   for (const MachineBasicBlock &MBB : MF) {
189     for (const MachineInstr &MI : MBB) {
190       unsigned Opcode = MI.getOpcode();
191       if (Opcode == FrameSetupOpcode || Opcode == FrameDestroyOpcode) {
192         unsigned Size = TII.getFrameSize(MI);
193         MaxCallFrameSize = std::max(MaxCallFrameSize, Size);
194         AdjustsStack = true;
195       } else if (MI.isInlineAsm()) {
196         // Some inline asm's need a stack frame, as indicated by operand 1.
197         unsigned ExtraInfo = MI.getOperand(InlineAsm::MIOp_ExtraInfo).getImm();
198         if (ExtraInfo & InlineAsm::Extra_IsAlignStack)
199           AdjustsStack = true;
200       }
201     }
202   }
203 }
204 
205 void MachineFrameInfo::print(const MachineFunction &MF, raw_ostream &OS) const{
206   if (Objects.empty()) return;
207 
208   const TargetFrameLowering *FI = MF.getSubtarget().getFrameLowering();
209   int ValOffset = (FI ? FI->getOffsetOfLocalArea() : 0);
210 
211   OS << "Frame Objects:\n";
212 
213   for (unsigned i = 0, e = Objects.size(); i != e; ++i) {
214     const StackObject &SO = Objects[i];
215     OS << "  fi#" << (int)(i-NumFixedObjects) << ": ";
216 
217     if (SO.StackID != 0)
218       OS << "id=" << SO.StackID << ' ';
219 
220     if (SO.Size == ~0ULL) {
221       OS << "dead\n";
222       continue;
223     }
224     if (SO.Size == 0)
225       OS << "variable sized";
226     else
227       OS << "size=" << SO.Size;
228     OS << ", align=" << SO.Alignment;
229 
230     if (i < NumFixedObjects)
231       OS << ", fixed";
232     if (i < NumFixedObjects || SO.SPOffset != -1) {
233       int64_t Off = SO.SPOffset - ValOffset;
234       OS << ", at location [SP";
235       if (Off > 0)
236         OS << "+" << Off;
237       else if (Off < 0)
238         OS << Off;
239       OS << "]";
240     }
241     OS << "\n";
242   }
243 }
244 
245 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
246 LLVM_DUMP_METHOD void MachineFrameInfo::dump(const MachineFunction &MF) const {
247   print(MF, dbgs());
248 }
249 #endif
250