1//===-- NVPTXPrologEpilogPass.cpp - NVPTX prolog/epilog inserter ----------===//
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// This file is a copy of the generic LLVM PrologEpilogInserter pass, modified
11// to remove unneeded functionality and to handle virtual registers. Most code
12// here is a copy of PrologEpilogInserter.cpp.
13//
14//===----------------------------------------------------------------------===//
15
16#include "NVPTX.h"
17#include "llvm/CodeGen/MachineFrameInfo.h"
18#include "llvm/CodeGen/MachineFunction.h"
19#include "llvm/CodeGen/MachineFunctionPass.h"
20#include "llvm/Pass.h"
21#include "llvm/Support/Debug.h"
22#include "llvm/Support/raw_ostream.h"
23#include "llvm/Target/TargetFrameLowering.h"
24#include "llvm/Target/TargetRegisterInfo.h"
25#include "llvm/Target/TargetSubtargetInfo.h"
26
27using namespace llvm;
28
29#define DEBUG_TYPE "nvptx-prolog-epilog"
30
31namespace {
32class NVPTXPrologEpilogPass : public MachineFunctionPass {
33public:
34  static char ID;
35  NVPTXPrologEpilogPass() : MachineFunctionPass(ID) {}
36
37  bool runOnMachineFunction(MachineFunction &MF) override;
38
39private:
40  void calculateFrameObjectOffsets(MachineFunction &Fn);
41};
42}
43
44MachineFunctionPass *llvm::createNVPTXPrologEpilogPass() {
45  return new NVPTXPrologEpilogPass();
46}
47
48char NVPTXPrologEpilogPass::ID = 0;
49
50bool NVPTXPrologEpilogPass::runOnMachineFunction(MachineFunction &MF) {
51  const TargetSubtargetInfo &STI = MF.getSubtarget();
52  const TargetFrameLowering &TFI = *STI.getFrameLowering();
53  const TargetRegisterInfo &TRI = *STI.getRegisterInfo();
54  bool Modified = false;
55
56  calculateFrameObjectOffsets(MF);
57
58  for (MachineFunction::iterator BB = MF.begin(), E = MF.end(); BB != E; ++BB) {
59    for (MachineBasicBlock::iterator I = BB->begin(); I != BB->end(); ++I) {
60      MachineInstr *MI = I;
61      for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
62        if (!MI->getOperand(i).isFI())
63          continue;
64        TRI.eliminateFrameIndex(MI, 0, i, nullptr);
65        Modified = true;
66      }
67    }
68  }
69
70  // Add function prolog/epilog
71  TFI.emitPrologue(MF);
72
73  for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I) {
74    // If last instruction is a return instruction, add an epilogue
75    if (!I->empty() && I->back().isReturn())
76      TFI.emitEpilogue(MF, *I);
77  }
78
79  return Modified;
80}
81
82/// AdjustStackOffset - Helper function used to adjust the stack frame offset.
83static inline void
84AdjustStackOffset(MachineFrameInfo *MFI, int FrameIdx,
85                  bool StackGrowsDown, int64_t &Offset,
86                  unsigned &MaxAlign) {
87  // If the stack grows down, add the object size to find the lowest address.
88  if (StackGrowsDown)
89    Offset += MFI->getObjectSize(FrameIdx);
90
91  unsigned Align = MFI->getObjectAlignment(FrameIdx);
92
93  // If the alignment of this object is greater than that of the stack, then
94  // increase the stack alignment to match.
95  MaxAlign = std::max(MaxAlign, Align);
96
97  // Adjust to alignment boundary.
98  Offset = (Offset + Align - 1) / Align * Align;
99
100  if (StackGrowsDown) {
101    DEBUG(dbgs() << "alloc FI(" << FrameIdx << ") at SP[" << -Offset << "]\n");
102    MFI->setObjectOffset(FrameIdx, -Offset); // Set the computed offset
103  } else {
104    DEBUG(dbgs() << "alloc FI(" << FrameIdx << ") at SP[" << Offset << "]\n");
105    MFI->setObjectOffset(FrameIdx, Offset);
106    Offset += MFI->getObjectSize(FrameIdx);
107  }
108}
109
110void
111NVPTXPrologEpilogPass::calculateFrameObjectOffsets(MachineFunction &Fn) {
112  const TargetFrameLowering &TFI = *Fn.getSubtarget().getFrameLowering();
113  const TargetRegisterInfo *RegInfo = Fn.getSubtarget().getRegisterInfo();
114
115  bool StackGrowsDown =
116    TFI.getStackGrowthDirection() == TargetFrameLowering::StackGrowsDown;
117
118  // Loop over all of the stack objects, assigning sequential addresses...
119  MachineFrameInfo *MFI = Fn.getFrameInfo();
120
121  // Start at the beginning of the local area.
122  // The Offset is the distance from the stack top in the direction
123  // of stack growth -- so it's always nonnegative.
124  int LocalAreaOffset = TFI.getOffsetOfLocalArea();
125  if (StackGrowsDown)
126    LocalAreaOffset = -LocalAreaOffset;
127  assert(LocalAreaOffset >= 0
128         && "Local area offset should be in direction of stack growth");
129  int64_t Offset = LocalAreaOffset;
130
131  // If there are fixed sized objects that are preallocated in the local area,
132  // non-fixed objects can't be allocated right at the start of local area.
133  // We currently don't support filling in holes in between fixed sized
134  // objects, so we adjust 'Offset' to point to the end of last fixed sized
135  // preallocated object.
136  for (int i = MFI->getObjectIndexBegin(); i != 0; ++i) {
137    int64_t FixedOff;
138    if (StackGrowsDown) {
139      // The maximum distance from the stack pointer is at lower address of
140      // the object -- which is given by offset. For down growing stack
141      // the offset is negative, so we negate the offset to get the distance.
142      FixedOff = -MFI->getObjectOffset(i);
143    } else {
144      // The maximum distance from the start pointer is at the upper
145      // address of the object.
146      FixedOff = MFI->getObjectOffset(i) + MFI->getObjectSize(i);
147    }
148    if (FixedOff > Offset) Offset = FixedOff;
149  }
150
151  // NOTE: We do not have a call stack
152
153  unsigned MaxAlign = MFI->getMaxAlignment();
154
155  // No scavenger
156
157  // FIXME: Once this is working, then enable flag will change to a target
158  // check for whether the frame is large enough to want to use virtual
159  // frame index registers. Functions which don't want/need this optimization
160  // will continue to use the existing code path.
161  if (MFI->getUseLocalStackAllocationBlock()) {
162    unsigned Align = MFI->getLocalFrameMaxAlign();
163
164    // Adjust to alignment boundary.
165    Offset = (Offset + Align - 1) / Align * Align;
166
167    DEBUG(dbgs() << "Local frame base offset: " << Offset << "\n");
168
169    // Resolve offsets for objects in the local block.
170    for (unsigned i = 0, e = MFI->getLocalFrameObjectCount(); i != e; ++i) {
171      std::pair<int, int64_t> Entry = MFI->getLocalFrameObjectMap(i);
172      int64_t FIOffset = (StackGrowsDown ? -Offset : Offset) + Entry.second;
173      DEBUG(dbgs() << "alloc FI(" << Entry.first << ") at SP[" <<
174            FIOffset << "]\n");
175      MFI->setObjectOffset(Entry.first, FIOffset);
176    }
177    // Allocate the local block
178    Offset += MFI->getLocalFrameSize();
179
180    MaxAlign = std::max(Align, MaxAlign);
181  }
182
183  // No stack protector
184
185  // Then assign frame offsets to stack objects that are not used to spill
186  // callee saved registers.
187  for (unsigned i = 0, e = MFI->getObjectIndexEnd(); i != e; ++i) {
188    if (MFI->isObjectPreAllocated(i) &&
189        MFI->getUseLocalStackAllocationBlock())
190      continue;
191    if (MFI->isDeadObjectIndex(i))
192      continue;
193
194    AdjustStackOffset(MFI, i, StackGrowsDown, Offset, MaxAlign);
195  }
196
197  // No scavenger
198
199  if (!TFI.targetHandlesStackFrameRounding()) {
200    // If we have reserved argument space for call sites in the function
201    // immediately on entry to the current function, count it as part of the
202    // overall stack size.
203    if (MFI->adjustsStack() && TFI.hasReservedCallFrame(Fn))
204      Offset += MFI->getMaxCallFrameSize();
205
206    // Round up the size to a multiple of the alignment.  If the function has
207    // any calls or alloca's, align to the target's StackAlignment value to
208    // ensure that the callee's frame or the alloca data is suitably aligned;
209    // otherwise, for leaf functions, align to the TransientStackAlignment
210    // value.
211    unsigned StackAlign;
212    if (MFI->adjustsStack() || MFI->hasVarSizedObjects() ||
213        (RegInfo->needsStackRealignment(Fn) && MFI->getObjectIndexEnd() != 0))
214      StackAlign = TFI.getStackAlignment();
215    else
216      StackAlign = TFI.getTransientStackAlignment();
217
218    // If the frame pointer is eliminated, all frame offsets will be relative to
219    // SP not FP. Align to MaxAlign so this works.
220    StackAlign = std::max(StackAlign, MaxAlign);
221    unsigned AlignMask = StackAlign - 1;
222    Offset = (Offset + AlignMask) & ~uint64_t(AlignMask);
223  }
224
225  // Update frame info to pretend that this is part of the stack...
226  int64_t StackSize = Offset - LocalAreaOffset;
227  MFI->setStackSize(StackSize);
228}
229