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