1//===- StatepointLowering.h - SDAGBuilder's statepoint code ---*- C++ -*---===//
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 includes support code use by SelectionDAGBuilder when lowering a
10// statepoint sequence in SelectionDAG IR.
11//
12//===----------------------------------------------------------------------===//
13
14#ifndef LLVM_LIB_CODEGEN_SELECTIONDAG_STATEPOINTLOWERING_H
15#define LLVM_LIB_CODEGEN_SELECTIONDAG_STATEPOINTLOWERING_H
16
17#include "llvm/ADT/DenseMap.h"
18#include "llvm/ADT/SmallBitVector.h"
19#include "llvm/ADT/SmallVector.h"
20#include "llvm/CodeGen/SelectionDAGNodes.h"
21#include "llvm/IR/IntrinsicInst.h"
22#include <cassert>
23
24namespace llvm {
25
26class SelectionDAGBuilder;
27
28/// This class tracks both per-statepoint and per-selectiondag information.
29/// For each statepoint it tracks locations of it's gc valuess (incoming and
30/// relocated) and list of gcreloc calls scheduled for visiting (this is
31/// used for a debug mode consistency check only).  The spill slot tracking
32/// works in concert with information in FunctionLoweringInfo.
33class StatepointLoweringState {
34public:
35  StatepointLoweringState() = default;
36
37  /// Reset all state tracking for a newly encountered safepoint.  Also
38  /// performs some consistency checking.
39  void startNewStatepoint(SelectionDAGBuilder &Builder);
40
41  /// Clear the memory usage of this object.  This is called from
42  /// SelectionDAGBuilder::clear.  We require this is never called in the
43  /// midst of processing a statepoint sequence.
44  void clear();
45
46  /// Returns the spill location of a value incoming to the current
47  /// statepoint.  Will return SDValue() if this value hasn't been
48  /// spilled.  Otherwise, the value has already been spilled and no
49  /// further action is required by the caller.
50  SDValue getLocation(SDValue Val) {
51    auto I = Locations.find(Val);
52    if (I == Locations.end())
53      return SDValue();
54    return I->second;
55  }
56
57  void setLocation(SDValue Val, SDValue Location) {
58    assert(!Locations.count(Val) &&
59           "Trying to allocate already allocated location");
60    Locations[Val] = Location;
61  }
62
63  /// Record the fact that we expect to encounter a given gc_relocate
64  /// before the next statepoint.  If we don't see it, we'll report
65  /// an assertion.
66  void scheduleRelocCall(const GCRelocateInst &RelocCall) {
67    // We are not interested in lowering dead instructions.
68    if (!RelocCall.use_empty())
69      PendingGCRelocateCalls.push_back(&RelocCall);
70  }
71
72  /// Remove this gc_relocate from the list we're expecting to see
73  /// before the next statepoint.  If we weren't expecting to see
74  /// it, we'll report an assertion.
75  void relocCallVisited(const GCRelocateInst &RelocCall) {
76    // We are not interested in lowering dead instructions.
77    if (RelocCall.use_empty())
78      return;
79    auto I = llvm::find(PendingGCRelocateCalls, &RelocCall);
80    assert(I != PendingGCRelocateCalls.end() &&
81           "Visited unexpected gcrelocate call");
82    PendingGCRelocateCalls.erase(I);
83  }
84
85  // TODO: Should add consistency tracking to ensure we encounter
86  // expected gc_result calls too.
87
88  /// Get a stack slot we can use to store an value of type ValueType.  This
89  /// will hopefully be a recylced slot from another statepoint.
90  SDValue allocateStackSlot(EVT ValueType, SelectionDAGBuilder &Builder);
91
92  void reserveStackSlot(int Offset) {
93    assert(Offset >= 0 && Offset < (int)AllocatedStackSlots.size() &&
94           "out of bounds");
95    assert(!AllocatedStackSlots.test(Offset) && "already reserved!");
96    assert(NextSlotToAllocate <= (unsigned)Offset && "consistency!");
97    AllocatedStackSlots.set(Offset);
98  }
99
100  bool isStackSlotAllocated(int Offset) {
101    assert(Offset >= 0 && Offset < (int)AllocatedStackSlots.size() &&
102           "out of bounds");
103    return AllocatedStackSlots.test(Offset);
104  }
105
106private:
107  /// Maps pre-relocation value (gc pointer directly incoming into statepoint)
108  /// into it's location (currently only stack slots)
109  DenseMap<SDValue, SDValue> Locations;
110
111  /// A boolean indicator for each slot listed in the FunctionInfo as to
112  /// whether it has been used in the current statepoint.  Since we try to
113  /// preserve stack slots across safepoints, there can be gaps in which
114  /// slots have been allocated.
115  SmallBitVector AllocatedStackSlots;
116
117  /// Points just beyond the last slot known to have been allocated
118  unsigned NextSlotToAllocate = 0;
119
120  /// Keep track of pending gcrelocate calls for consistency check
121  SmallVector<const GCRelocateInst *, 10> PendingGCRelocateCalls;
122};
123
124} // end namespace llvm
125
126#endif // LLVM_LIB_CODEGEN_SELECTIONDAG_STATEPOINTLOWERING_H
127