1//===-- NVPTXPrologEpilogPass.cpp - NVPTX prolog/epilog inserter ----------===//
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// This file is a copy of the generic LLVM PrologEpilogInserter pass, modified
10// to remove unneeded functionality and to handle virtual registers. Most code
11// here is a copy of PrologEpilogInserter.cpp.
12//
13//===----------------------------------------------------------------------===//
14
15#include "NVPTX.h"
16#include "llvm/CodeGen/MachineFrameInfo.h"
17#include "llvm/CodeGen/MachineFunction.h"
18#include "llvm/CodeGen/MachineFunctionPass.h"
19#include "llvm/CodeGen/TargetFrameLowering.h"
20#include "llvm/CodeGen/TargetRegisterInfo.h"
21#include "llvm/CodeGen/TargetSubtargetInfo.h"
22#include "llvm/IR/DebugInfoMetadata.h"
23#include "llvm/Pass.h"
24#include "llvm/Support/Debug.h"
25#include "llvm/Support/raw_ostream.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 (MachineBasicBlock &MBB : MF) {
59    for (MachineInstr &MI : MBB) {
60      for (unsigned i = 0, e = MI.getNumOperands(); i != e; ++i) {
61        if (!MI.getOperand(i).isFI())
62          continue;
63
64        // Frame indices in debug values are encoded in a target independent
65        // way with simply the frame index and offset rather than any
66        // target-specific addressing mode.
67        if (MI.isDebugValue()) {
68          assert(i == 0 && "Frame indices can only appear as the first "
69                           "operand of a DBG_VALUE machine instruction");
70          unsigned Reg;
71          int64_t Offset =
72              TFI.getFrameIndexReference(MF, MI.getOperand(0).getIndex(), Reg);
73          MI.getOperand(0).ChangeToRegister(Reg, /*isDef=*/false);
74          MI.getOperand(0).setIsDebug();
75          auto *DIExpr = DIExpression::prepend(
76              MI.getDebugExpression(), DIExpression::ApplyOffset, Offset);
77          MI.getOperand(3).setMetadata(DIExpr);
78          continue;
79        }
80
81        TRI.eliminateFrameIndex(MI, 0, i, nullptr);
82        Modified = true;
83      }
84    }
85  }
86
87  // Add function prolog/epilog
88  TFI.emitPrologue(MF, MF.front());
89
90  for (MachineFunction::iterator I = MF.begin(), E = MF.end(); I != E; ++I) {
91    // If last instruction is a return instruction, add an epilogue
92    if (I->isReturnBlock())
93      TFI.emitEpilogue(MF, *I);
94  }
95
96  return Modified;
97}
98
99/// AdjustStackOffset - Helper function used to adjust the stack frame offset.
100static inline void
101AdjustStackOffset(MachineFrameInfo &MFI, int FrameIdx,
102                  bool StackGrowsDown, int64_t &Offset,
103                  unsigned &MaxAlign) {
104  // If the stack grows down, add the object size to find the lowest address.
105  if (StackGrowsDown)
106    Offset += MFI.getObjectSize(FrameIdx);
107
108  unsigned Align = MFI.getObjectAlignment(FrameIdx);
109
110  // If the alignment of this object is greater than that of the stack, then
111  // increase the stack alignment to match.
112  MaxAlign = std::max(MaxAlign, Align);
113
114  // Adjust to alignment boundary.
115  Offset = (Offset + Align - 1) / Align * Align;
116
117  if (StackGrowsDown) {
118    LLVM_DEBUG(dbgs() << "alloc FI(" << FrameIdx << ") at SP[" << -Offset
119                      << "]\n");
120    MFI.setObjectOffset(FrameIdx, -Offset); // Set the computed offset
121  } else {
122    LLVM_DEBUG(dbgs() << "alloc FI(" << FrameIdx << ") at SP[" << Offset
123                      << "]\n");
124    MFI.setObjectOffset(FrameIdx, Offset);
125    Offset += MFI.getObjectSize(FrameIdx);
126  }
127}
128
129void
130NVPTXPrologEpilogPass::calculateFrameObjectOffsets(MachineFunction &Fn) {
131  const TargetFrameLowering &TFI = *Fn.getSubtarget().getFrameLowering();
132  const TargetRegisterInfo *RegInfo = Fn.getSubtarget().getRegisterInfo();
133
134  bool StackGrowsDown =
135    TFI.getStackGrowthDirection() == TargetFrameLowering::StackGrowsDown;
136
137  // Loop over all of the stack objects, assigning sequential addresses...
138  MachineFrameInfo &MFI = Fn.getFrameInfo();
139
140  // Start at the beginning of the local area.
141  // The Offset is the distance from the stack top in the direction
142  // of stack growth -- so it's always nonnegative.
143  int LocalAreaOffset = TFI.getOffsetOfLocalArea();
144  if (StackGrowsDown)
145    LocalAreaOffset = -LocalAreaOffset;
146  assert(LocalAreaOffset >= 0
147         && "Local area offset should be in direction of stack growth");
148  int64_t Offset = LocalAreaOffset;
149
150  // If there are fixed sized objects that are preallocated in the local area,
151  // non-fixed objects can't be allocated right at the start of local area.
152  // We currently don't support filling in holes in between fixed sized
153  // objects, so we adjust 'Offset' to point to the end of last fixed sized
154  // preallocated object.
155  for (int i = MFI.getObjectIndexBegin(); i != 0; ++i) {
156    int64_t FixedOff;
157    if (StackGrowsDown) {
158      // The maximum distance from the stack pointer is at lower address of
159      // the object -- which is given by offset. For down growing stack
160      // the offset is negative, so we negate the offset to get the distance.
161      FixedOff = -MFI.getObjectOffset(i);
162    } else {
163      // The maximum distance from the start pointer is at the upper
164      // address of the object.
165      FixedOff = MFI.getObjectOffset(i) + MFI.getObjectSize(i);
166    }
167    if (FixedOff > Offset) Offset = FixedOff;
168  }
169
170  // NOTE: We do not have a call stack
171
172  unsigned MaxAlign = MFI.getMaxAlignment();
173
174  // No scavenger
175
176  // FIXME: Once this is working, then enable flag will change to a target
177  // check for whether the frame is large enough to want to use virtual
178  // frame index registers. Functions which don't want/need this optimization
179  // will continue to use the existing code path.
180  if (MFI.getUseLocalStackAllocationBlock()) {
181    unsigned Align = MFI.getLocalFrameMaxAlign().value();
182
183    // Adjust to alignment boundary.
184    Offset = (Offset + Align - 1) / Align * Align;
185
186    LLVM_DEBUG(dbgs() << "Local frame base offset: " << Offset << "\n");
187
188    // Resolve offsets for objects in the local block.
189    for (unsigned i = 0, e = MFI.getLocalFrameObjectCount(); i != e; ++i) {
190      std::pair<int, int64_t> Entry = MFI.getLocalFrameObjectMap(i);
191      int64_t FIOffset = (StackGrowsDown ? -Offset : Offset) + Entry.second;
192      LLVM_DEBUG(dbgs() << "alloc FI(" << Entry.first << ") at SP[" << FIOffset
193                        << "]\n");
194      MFI.setObjectOffset(Entry.first, FIOffset);
195    }
196    // Allocate the local block
197    Offset += MFI.getLocalFrameSize();
198
199    MaxAlign = std::max(Align, MaxAlign);
200  }
201
202  // No stack protector
203
204  // Then assign frame offsets to stack objects that are not used to spill
205  // callee saved registers.
206  for (unsigned i = 0, e = MFI.getObjectIndexEnd(); i != e; ++i) {
207    if (MFI.isObjectPreAllocated(i) &&
208        MFI.getUseLocalStackAllocationBlock())
209      continue;
210    if (MFI.isDeadObjectIndex(i))
211      continue;
212
213    AdjustStackOffset(MFI, i, StackGrowsDown, Offset, MaxAlign);
214  }
215
216  // No scavenger
217
218  if (!TFI.targetHandlesStackFrameRounding()) {
219    // If we have reserved argument space for call sites in the function
220    // immediately on entry to the current function, count it as part of the
221    // overall stack size.
222    if (MFI.adjustsStack() && TFI.hasReservedCallFrame(Fn))
223      Offset += MFI.getMaxCallFrameSize();
224
225    // Round up the size to a multiple of the alignment.  If the function has
226    // any calls or alloca's, align to the target's StackAlignment value to
227    // ensure that the callee's frame or the alloca data is suitably aligned;
228    // otherwise, for leaf functions, align to the TransientStackAlignment
229    // value.
230    unsigned StackAlign;
231    if (MFI.adjustsStack() || MFI.hasVarSizedObjects() ||
232        (RegInfo->needsStackRealignment(Fn) && MFI.getObjectIndexEnd() != 0))
233      StackAlign = TFI.getStackAlignment();
234    else
235      StackAlign = TFI.getTransientStackAlignment();
236
237    // If the frame pointer is eliminated, all frame offsets will be relative to
238    // SP not FP. Align to MaxAlign so this works.
239    StackAlign = std::max(StackAlign, MaxAlign);
240    unsigned AlignMask = StackAlign - 1;
241    Offset = (Offset + AlignMask) & ~uint64_t(AlignMask);
242  }
243
244  // Update frame info to pretend that this is part of the stack...
245  int64_t StackSize = Offset - LocalAreaOffset;
246  MFI.setStackSize(StackSize);
247}
248