1 //===- GISelWorkList.h - Worklist for GISel passes ----*- 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 #ifndef LLVM_GISEL_WORKLIST_H
10 #define LLVM_GISEL_WORKLIST_H
11 
12 #include "llvm/ADT/DenseMap.h"
13 #include "llvm/ADT/SmallVector.h"
14 #include "llvm/CodeGen/MachineBasicBlock.h"
15 #include "llvm/CodeGen/MachineInstr.h"
16 #include "llvm/Support/Debug.h"
17 
18 namespace llvm {
19 
20 class MachineInstr;
21 class MachineFunction;
22 
23 // Worklist which mostly works similar to InstCombineWorkList, but on
24 // MachineInstrs. The main difference with something like a SetVector is that
25 // erasing an element doesn't move all elements over one place - instead just
26 // nulls out the element of the vector.
27 //
28 // FIXME: Does it make sense to factor out common code with the
29 // instcombinerWorkList?
30 template<unsigned N>
31 class GISelWorkList {
32   SmallVector<MachineInstr *, N> Worklist;
33   DenseMap<MachineInstr *, unsigned> WorklistMap;
34 
35 #ifndef NDEBUG
36   bool Finalized = true;
37 #endif
38 
39 public:
40   GISelWorkList() : WorklistMap(N) {}
41 
42   bool empty() const { return WorklistMap.empty(); }
43 
44   unsigned size() const { return WorklistMap.size(); }
45 
46   // Since we don't know ahead of time how many instructions we're going to add
47   // to the worklist, and migrating densemap's elements is quite expensive
48   // everytime we resize, only insert to the smallvector (typically during the
49   // initial phase of populating lists). Before the worklist can be used,
50   // finalize should be called. Also assert with NDEBUG if list is ever used
51   // without finalizing. Note that unlike insert, we won't check for duplicates
52   // - so the ideal place to use this is during the initial prepopulating phase
53   // of most passes.
54   void deferred_insert(MachineInstr *I) {
55     Worklist.push_back(I);
56 #ifndef NDEBUG
57     Finalized = false;
58 #endif
59   }
60 
61   // This should only be called when using deferred_insert.
62   // This asserts that the WorklistMap is empty, and then
63   // inserts all the elements in the Worklist into the map.
64   // It also asserts if there are any duplicate elements found.
65   void finalize() {
66     assert(WorklistMap.empty() && "Expecting empty worklistmap");
67     if (Worklist.size() > N)
68       WorklistMap.reserve(Worklist.size());
69     for (unsigned i = 0; i < Worklist.size(); ++i)
70       if (!WorklistMap.try_emplace(Worklist[i], i).second)
71         llvm_unreachable("Duplicate elements in the list");
72 #ifndef NDEBUG
73     Finalized = true;
74 #endif
75   }
76 
77   /// Add the specified instruction to the worklist if it isn't already in it.
78   void insert(MachineInstr *I) {
79     assert(Finalized && "GISelWorkList used without finalizing");
80     if (WorklistMap.try_emplace(I, Worklist.size()).second)
81       Worklist.push_back(I);
82   }
83 
84   /// Remove I from the worklist if it exists.
85   void remove(const MachineInstr *I) {
86     assert((Finalized || WorklistMap.empty()) && "Neither finalized nor empty");
87     auto It = WorklistMap.find(I);
88     if (It == WorklistMap.end())
89       return; // Not in worklist.
90 
91     // Don't bother moving everything down, just null out the slot.
92     Worklist[It->second] = nullptr;
93 
94     WorklistMap.erase(It);
95   }
96 
97   void clear() {
98     Worklist.clear();
99     WorklistMap.clear();
100   }
101 
102   MachineInstr *pop_back_val() {
103     assert(Finalized && "GISelWorkList used without finalizing");
104     MachineInstr *I;
105     do {
106       I = Worklist.pop_back_val();
107     } while(!I);
108     assert(I && "Pop back on empty worklist");
109     WorklistMap.erase(I);
110     return I;
111   }
112 };
113 
114 } // end namespace llvm.
115 
116 #endif
117