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