NVPTXPrologEpilogPass.cpp revision dce4a407a24b04eebc6a376f8e62b41aaa7b071f 
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
26using namespace llvm;
27
28#define DEBUG_TYPE "nvptx-prolog-epilog"
29
30namespace {
31class NVPTXPrologEpilogPass : public MachineFunctionPass {
32public:
33  static char ID;
34  NVPTXPrologEpilogPass() : MachineFunctionPass(ID) {}
35
36  bool runOnMachineFunction(MachineFunction &MF) override;
37
38private:
39  void calculateFrameObjectOffsets(MachineFunction &Fn);
40};
41}
42
43MachineFunctionPass *llvm::createNVPTXPrologEpilogPass() {
44  return new NVPTXPrologEpilogPass();
45}
46
47char NVPTXPrologEpilogPass::ID = 0;
48
49bool NVPTXPrologEpilogPass::runOnMachineFunction(MachineFunction &MF) {
50  const TargetMachine &TM = MF.getTarget();
51  const TargetFrameLowering &TFI = *TM.getFrameLowering();
52  const TargetRegisterInfo &TRI = *TM.getRegisterInfo();
53  bool Modified = false;
54
55  calculateFrameObjectOffsets(MF);
56
57  for (MachineFunction::iterator BB = MF.begin(), E = MF.end(); BB != E; ++BB) {
58    for (MachineBasicBlock::iterator I = BB->begin(); I != BB->end(); ++I) {
59      MachineInstr *MI = I;
60      for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
61        if (!MI->getOperand(i).isFI())
62          continue;
63        TRI.eliminateFrameIndex(MI, 0, i, nullptr);
64        Modified = true;
65      }
66    }
67  }
68
69  // Add function prolog/epilog
70  TFI.emitPrologue(MF);
71
72  for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I) {
73    // If last instruction is a return instruction, add an epilogue
74    if (!I->empty() && I->back().isReturn())
75      TFI.emitEpilogue(MF, *I);
76  }
77
78  return Modified;
79}
80
81/// AdjustStackOffset - Helper function used to adjust the stack frame offset.
82static inline void
83AdjustStackOffset(MachineFrameInfo *MFI, int FrameIdx,
84                  bool StackGrowsDown, int64_t &Offset,
85                  unsigned &MaxAlign) {
86  // If the stack grows down, add the object size to find the lowest address.
87  if (StackGrowsDown)
88    Offset += MFI->getObjectSize(FrameIdx);
89
90  unsigned Align = MFI->getObjectAlignment(FrameIdx);
91
92  // If the alignment of this object is greater than that of the stack, then
93  // increase the stack alignment to match.
94  MaxAlign = std::max(MaxAlign, Align);
95
96  // Adjust to alignment boundary.
97  Offset = (Offset + Align - 1) / Align * Align;
98
99  if (StackGrowsDown) {
100    DEBUG(dbgs() << "alloc FI(" << FrameIdx << ") at SP[" << -Offset << "]\n");
101    MFI->setObjectOffset(FrameIdx, -Offset); // Set the computed offset
102  } else {
103    DEBUG(dbgs() << "alloc FI(" << FrameIdx << ") at SP[" << Offset << "]\n");
104    MFI->setObjectOffset(FrameIdx, Offset);
105    Offset += MFI->getObjectSize(FrameIdx);
106  }
107}
108
109void
110NVPTXPrologEpilogPass::calculateFrameObjectOffsets(MachineFunction &Fn) {
111  const TargetFrameLowering &TFI = *Fn.getTarget().getFrameLowering();
112  const TargetRegisterInfo *RegInfo = Fn.getTarget().getRegisterInfo();
113
114  bool StackGrowsDown =
115    TFI.getStackGrowthDirection() == TargetFrameLowering::StackGrowsDown;
116
117  // Loop over all of the stack objects, assigning sequential addresses...
118  MachineFrameInfo *MFI = Fn.getFrameInfo();
119
120  // Start at the beginning of the local area.
121  // The Offset is the distance from the stack top in the direction
122  // of stack growth -- so it's always nonnegative.
123  int LocalAreaOffset = TFI.getOffsetOfLocalArea();
124  if (StackGrowsDown)
125    LocalAreaOffset = -LocalAreaOffset;
126  assert(LocalAreaOffset >= 0
127         && "Local area offset should be in direction of stack growth");
128  int64_t Offset = LocalAreaOffset;
129
130  // If there are fixed sized objects that are preallocated in the local area,
131  // non-fixed objects can't be allocated right at the start of local area.
132  // We currently don't support filling in holes in between fixed sized
133  // objects, so we adjust 'Offset' to point to the end of last fixed sized
134  // preallocated object.
135  for (int i = MFI->getObjectIndexBegin(); i != 0; ++i) {
136    int64_t FixedOff;
137    if (StackGrowsDown) {
138      // The maximum distance from the stack pointer is at lower address of
139      // the object -- which is given by offset. For down growing stack
140      // the offset is negative, so we negate the offset to get the distance.
141      FixedOff = -MFI->getObjectOffset(i);
142    } else {
143      // The maximum distance from the start pointer is at the upper
144      // address of the object.
145      FixedOff = MFI->getObjectOffset(i) + MFI->getObjectSize(i);
146    }
147    if (FixedOff > Offset) Offset = FixedOff;
148  }
149
150  // NOTE: We do not have a call stack
151
152  unsigned MaxAlign = MFI->getMaxAlignment();
153
154  // No scavenger
155
156  // FIXME: Once this is working, then enable flag will change to a target
157  // check for whether the frame is large enough to want to use virtual
158  // frame index registers. Functions which don't want/need this optimization
159  // will continue to use the existing code path.
160  if (MFI->getUseLocalStackAllocationBlock()) {
161    unsigned Align = MFI->getLocalFrameMaxAlign();
162
163    // Adjust to alignment boundary.
164    Offset = (Offset + Align - 1) / Align * Align;
165
166    DEBUG(dbgs() << "Local frame base offset: " << Offset << "\n");
167
168    // Resolve offsets for objects in the local block.
169    for (unsigned i = 0, e = MFI->getLocalFrameObjectCount(); i != e; ++i) {
170      std::pair<int, int64_t> Entry = MFI->getLocalFrameObjectMap(i);
171      int64_t FIOffset = (StackGrowsDown ? -Offset : Offset) + Entry.second;
172      DEBUG(dbgs() << "alloc FI(" << Entry.first << ") at SP[" <<
173            FIOffset << "]\n");
174      MFI->setObjectOffset(Entry.first, FIOffset);
175    }
176    // Allocate the local block
177    Offset += MFI->getLocalFrameSize();
178
179    MaxAlign = std::max(Align, MaxAlign);
180  }
181
182  // No stack protector
183
184  // Then assign frame offsets to stack objects that are not used to spill
185  // callee saved registers.
186  for (unsigned i = 0, e = MFI->getObjectIndexEnd(); i != e; ++i) {
187    if (MFI->isObjectPreAllocated(i) &&
188        MFI->getUseLocalStackAllocationBlock())
189      continue;
190    if (MFI->isDeadObjectIndex(i))
191      continue;
192
193    AdjustStackOffset(MFI, i, StackGrowsDown, Offset, MaxAlign);
194  }
195
196  // No scavenger
197
198  if (!TFI.targetHandlesStackFrameRounding()) {
199    // If we have reserved argument space for call sites in the function
200    // immediately on entry to the current function, count it as part of the
201    // overall stack size.
202    if (MFI->adjustsStack() && TFI.hasReservedCallFrame(Fn))
203      Offset += MFI->getMaxCallFrameSize();
204
205    // Round up the size to a multiple of the alignment.  If the function has
206    // any calls or alloca's, align to the target's StackAlignment value to
207    // ensure that the callee's frame or the alloca data is suitably aligned;
208    // otherwise, for leaf functions, align to the TransientStackAlignment
209    // value.
210    unsigned StackAlign;
211    if (MFI->adjustsStack() || MFI->hasVarSizedObjects() ||
212        (RegInfo->needsStackRealignment(Fn) && MFI->getObjectIndexEnd() != 0))
213      StackAlign = TFI.getStackAlignment();
214    else
215      StackAlign = TFI.getTransientStackAlignment();
216
217    // If the frame pointer is eliminated, all frame offsets will be relative to
218    // SP not FP. Align to MaxAlign so this works.
219    StackAlign = std::max(StackAlign, MaxAlign);
220    unsigned AlignMask = StackAlign - 1;
221    Offset = (Offset + AlignMask) & ~uint64_t(AlignMask);
222  }
223
224  // Update frame info to pretend that this is part of the stack...
225  int64_t StackSize = Offset - LocalAreaOffset;
226  MFI->setStackSize(StackSize);
227}
228