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/STLExtras.h"
19 #include "llvm/ADT/SmallBitVector.h"
20 #include "llvm/ADT/SmallVector.h"
21 #include "llvm/CodeGen/SelectionDAGNodes.h"
22 #include "llvm/CodeGen/ValueTypes.h"
23 #include <cassert>
24 
25 namespace llvm {
26 
27 class CallInst;
28 class SelectionDAGBuilder;
29 
30 /// This class tracks both per-statepoint and per-selectiondag information.
31 /// For each statepoint it tracks locations of it's gc valuess (incoming and
32 /// relocated) and list of gcreloc calls scheduled for visiting (this is
33 /// used for a debug mode consistency check only).  The spill slot tracking
34 /// works in concert with information in FunctionLoweringInfo.
35 class StatepointLoweringState {
36 public:
37   StatepointLoweringState() = default;
38 
39   /// Reset all state tracking for a newly encountered safepoint.  Also
40   /// performs some consistency checking.
41   void startNewStatepoint(SelectionDAGBuilder &Builder);
42 
43   /// Clear the memory usage of this object.  This is called from
44   /// SelectionDAGBuilder::clear.  We require this is never called in the
45   /// midst of processing a statepoint sequence.
46   void clear();
47 
48   /// Returns the spill location of a value incoming to the current
49   /// statepoint.  Will return SDValue() if this value hasn't been
50   /// spilled.  Otherwise, the value has already been spilled and no
51   /// further action is required by the caller.
52   SDValue getLocation(SDValue Val) {
53     auto I = Locations.find(Val);
54     if (I == Locations.end())
55       return SDValue();
56     return I->second;
57   }
58 
59   void setLocation(SDValue Val, SDValue Location) {
60     assert(!Locations.count(Val) &&
61            "Trying to allocate already allocated location");
62     Locations[Val] = Location;
63   }
64 
65   /// Record the fact that we expect to encounter a given gc_relocate
66   /// before the next statepoint.  If we don't see it, we'll report
67   /// an assertion.
68   void scheduleRelocCall(const CallInst &RelocCall) {
69     // We are not interested in lowering dead instructions.
70     if (!RelocCall.use_empty())
71       PendingGCRelocateCalls.push_back(&RelocCall);
72   }
73 
74   /// Remove this gc_relocate from the list we're expecting to see
75   /// before the next statepoint.  If we weren't expecting to see
76   /// it, we'll report an assertion.
77   void relocCallVisited(const CallInst &RelocCall) {
78     // We are not interested in lowering dead instructions.
79     if (RelocCall.use_empty())
80       return;
81     auto I = llvm::find(PendingGCRelocateCalls, &RelocCall);
82     assert(I != PendingGCRelocateCalls.end() &&
83            "Visited unexpected gcrelocate call");
84     PendingGCRelocateCalls.erase(I);
85   }
86 
87   // TODO: Should add consistency tracking to ensure we encounter
88   // expected gc_result calls too.
89 
90   /// Get a stack slot we can use to store an value of type ValueType.  This
91   /// will hopefully be a recylced slot from another statepoint.
92   SDValue allocateStackSlot(EVT ValueType, SelectionDAGBuilder &Builder);
93 
94   void reserveStackSlot(int Offset) {
95     assert(Offset >= 0 && Offset < (int)AllocatedStackSlots.size() &&
96            "out of bounds");
97     assert(!AllocatedStackSlots.test(Offset) && "already reserved!");
98     assert(NextSlotToAllocate <= (unsigned)Offset && "consistency!");
99     AllocatedStackSlots.set(Offset);
100   }
101 
102   bool isStackSlotAllocated(int Offset) {
103     assert(Offset >= 0 && Offset < (int)AllocatedStackSlots.size() &&
104            "out of bounds");
105     return AllocatedStackSlots.test(Offset);
106   }
107 
108 private:
109   /// Maps pre-relocation value (gc pointer directly incoming into statepoint)
110   /// into it's location (currently only stack slots)
111   DenseMap<SDValue, SDValue> Locations;
112 
113   /// A boolean indicator for each slot listed in the FunctionInfo as to
114   /// whether it has been used in the current statepoint.  Since we try to
115   /// preserve stack slots across safepoints, there can be gaps in which
116   /// slots have been allocated.
117   SmallBitVector AllocatedStackSlots;
118 
119   /// Points just beyond the last slot known to have been allocated
120   unsigned NextSlotToAllocate = 0;
121 
122   /// Keep track of pending gcrelocate calls for consistency check
123   SmallVector<const CallInst *, 10> PendingGCRelocateCalls;
124 };
125 
126 } // end namespace llvm
127 
128 #endif // LLVM_LIB_CODEGEN_SELECTIONDAG_STATEPOINTLOWERING_H
129