1 //===- PhiValues.cpp - Phi Value Analysis ---------------------------------===//
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 #include "llvm/Analysis/PhiValues.h"
10 #include "llvm/ADT/SmallVector.h"
11 #include "llvm/IR/Instructions.h"
12 #include "llvm/InitializePasses.h"
13 
14 using namespace llvm;
15 
16 void PhiValues::PhiValuesCallbackVH::deleted() {
17   PV->invalidateValue(getValPtr());
18 }
19 
20 void PhiValues::PhiValuesCallbackVH::allUsesReplacedWith(Value *) {
21   // We could potentially update the cached values we have with the new value,
22   // but it's simpler to just treat the old value as invalidated.
23   PV->invalidateValue(getValPtr());
24 }
25 
26 bool PhiValues::invalidate(Function &, const PreservedAnalyses &PA,
27                            FunctionAnalysisManager::Invalidator &) {
28   // PhiValues is invalidated if it isn't preserved.
29   auto PAC = PA.getChecker<PhiValuesAnalysis>();
30   return !(PAC.preserved() || PAC.preservedSet<AllAnalysesOn<Function>>());
31 }
32 
33 // The goal here is to find all of the non-phi values reachable from this phi,
34 // and to do the same for all of the phis reachable from this phi, as doing so
35 // is necessary anyway in order to get the values for this phi. We do this using
36 // Tarjan's algorithm with Nuutila's improvements to find the strongly connected
37 // components of the phi graph rooted in this phi:
38 //  * All phis in a strongly connected component will have the same reachable
39 //    non-phi values. The SCC may not be the maximal subgraph for that set of
40 //    reachable values, but finding out that isn't really necessary (it would
41 //    only reduce the amount of memory needed to store the values).
42 //  * Tarjan's algorithm completes components in a bottom-up manner, i.e. it
43 //    never completes a component before the components reachable from it have
44 //    been completed. This means that when we complete a component we have
45 //    everything we need to collect the values reachable from that component.
46 //  * We collect both the non-phi values reachable from each SCC, as that's what
47 //    we're ultimately interested in, and all of the reachable values, i.e.
48 //    including phis, as that makes invalidateValue easier.
49 void PhiValues::processPhi(const PHINode *Phi,
50                            SmallVectorImpl<const PHINode *> &Stack) {
51   // Initialize the phi with the next depth number.
52   assert(DepthMap.lookup(Phi) == 0);
53   assert(NextDepthNumber != UINT_MAX);
54   unsigned int RootDepthNumber = ++NextDepthNumber;
55   DepthMap[Phi] = RootDepthNumber;
56 
57   // Recursively process the incoming phis of this phi.
58   TrackedValues.insert(PhiValuesCallbackVH(const_cast<PHINode *>(Phi), this));
59   for (Value *PhiOp : Phi->incoming_values()) {
60     if (PHINode *PhiPhiOp = dyn_cast<PHINode>(PhiOp)) {
61       // Recurse if the phi has not yet been visited.
62       unsigned int OpDepthNumber = DepthMap.lookup(PhiPhiOp);
63       if (OpDepthNumber == 0) {
64         processPhi(PhiPhiOp, Stack);
65         OpDepthNumber = DepthMap.lookup(PhiPhiOp);
66         assert(OpDepthNumber != 0);
67       }
68       // If the phi did not become part of a component then this phi and that
69       // phi are part of the same component, so adjust the depth number.
70       if (!ReachableMap.count(OpDepthNumber))
71         DepthMap[Phi] = std::min(DepthMap[Phi], OpDepthNumber);
72     } else {
73       TrackedValues.insert(PhiValuesCallbackVH(PhiOp, this));
74     }
75   }
76 
77   // Now that incoming phis have been handled, push this phi to the stack.
78   Stack.push_back(Phi);
79 
80   // If the depth number has not changed then we've finished collecting the phis
81   // of a strongly connected component.
82   if (DepthMap[Phi] == RootDepthNumber) {
83     // Collect the reachable values for this component. The phis of this
84     // component will be those on top of the depth stack with the same or
85     // greater depth number.
86     ConstValueSet &Reachable = ReachableMap[RootDepthNumber];
87     while (true) {
88       const PHINode *ComponentPhi = Stack.pop_back_val();
89       Reachable.insert(ComponentPhi);
90 
91       for (Value *Op : ComponentPhi->incoming_values()) {
92         if (PHINode *PhiOp = dyn_cast<PHINode>(Op)) {
93           // If this phi is not part of the same component then that component
94           // is guaranteed to have been completed before this one. Therefore we
95           // can just add its reachable values to the reachable values of this
96           // component.
97           unsigned int OpDepthNumber = DepthMap[PhiOp];
98           if (OpDepthNumber != RootDepthNumber) {
99             auto It = ReachableMap.find(OpDepthNumber);
100             if (It != ReachableMap.end())
101               Reachable.insert(It->second.begin(), It->second.end());
102           }
103         } else
104           Reachable.insert(Op);
105       }
106 
107       if (Stack.empty())
108         break;
109 
110       unsigned int &ComponentDepthNumber = DepthMap[Stack.back()];
111       if (ComponentDepthNumber < RootDepthNumber)
112         break;
113 
114       ComponentDepthNumber = RootDepthNumber;
115     }
116 
117     // Filter out phis to get the non-phi reachable values.
118     ValueSet &NonPhi = NonPhiReachableMap[RootDepthNumber];
119     for (const Value *V : Reachable)
120       if (!isa<PHINode>(V))
121         NonPhi.insert(const_cast<Value *>(V));
122   }
123 }
124 
125 const PhiValues::ValueSet &PhiValues::getValuesForPhi(const PHINode *PN) {
126   unsigned int DepthNumber = DepthMap.lookup(PN);
127   if (DepthNumber == 0) {
128     SmallVector<const PHINode *, 8> Stack;
129     processPhi(PN, Stack);
130     DepthNumber = DepthMap.lookup(PN);
131     assert(Stack.empty());
132     assert(DepthNumber != 0);
133   }
134   return NonPhiReachableMap[DepthNumber];
135 }
136 
137 void PhiValues::invalidateValue(const Value *V) {
138   // Components that can reach V are invalid.
139   SmallVector<unsigned int, 8> InvalidComponents;
140   for (auto &Pair : ReachableMap)
141     if (Pair.second.count(V))
142       InvalidComponents.push_back(Pair.first);
143 
144   for (unsigned int N : InvalidComponents) {
145     for (const Value *V : ReachableMap[N])
146       if (const PHINode *PN = dyn_cast<PHINode>(V))
147         DepthMap.erase(PN);
148     NonPhiReachableMap.erase(N);
149     ReachableMap.erase(N);
150   }
151   // This value is no longer tracked
152   auto It = TrackedValues.find_as(V);
153   if (It != TrackedValues.end())
154     TrackedValues.erase(It);
155 }
156 
157 void PhiValues::releaseMemory() {
158   DepthMap.clear();
159   NonPhiReachableMap.clear();
160   ReachableMap.clear();
161 }
162 
163 void PhiValues::print(raw_ostream &OS) const {
164   // Iterate through the phi nodes of the function rather than iterating through
165   // DepthMap in order to get predictable ordering.
166   for (const BasicBlock &BB : F) {
167     for (const PHINode &PN : BB.phis()) {
168       OS << "PHI ";
169       PN.printAsOperand(OS, false);
170       OS << " has values:\n";
171       unsigned int N = DepthMap.lookup(&PN);
172       auto It = NonPhiReachableMap.find(N);
173       if (It == NonPhiReachableMap.end())
174         OS << "  UNKNOWN\n";
175       else if (It->second.empty())
176         OS << "  NONE\n";
177       else
178         for (Value *V : It->second)
179           // Printing of an instruction prints two spaces at the start, so
180           // handle instructions and everything else slightly differently in
181           // order to get consistent indenting.
182           if (Instruction *I = dyn_cast<Instruction>(V))
183             OS << *I << "\n";
184           else
185             OS << "  " << *V << "\n";
186     }
187   }
188 }
189 
190 AnalysisKey PhiValuesAnalysis::Key;
191 PhiValues PhiValuesAnalysis::run(Function &F, FunctionAnalysisManager &) {
192   return PhiValues(F);
193 }
194 
195 PreservedAnalyses PhiValuesPrinterPass::run(Function &F,
196                                             FunctionAnalysisManager &AM) {
197   OS << "PHI Values for function: " << F.getName() << "\n";
198   PhiValues &PI = AM.getResult<PhiValuesAnalysis>(F);
199   for (const BasicBlock &BB : F)
200     for (const PHINode &PN : BB.phis())
201       PI.getValuesForPhi(&PN);
202   PI.print(OS);
203   return PreservedAnalyses::all();
204 }
205 
206 PhiValuesWrapperPass::PhiValuesWrapperPass() : FunctionPass(ID) {
207   initializePhiValuesWrapperPassPass(*PassRegistry::getPassRegistry());
208 }
209 
210 bool PhiValuesWrapperPass::runOnFunction(Function &F) {
211   Result.reset(new PhiValues(F));
212   return false;
213 }
214 
215 void PhiValuesWrapperPass::releaseMemory() {
216   Result->releaseMemory();
217 }
218 
219 void PhiValuesWrapperPass::getAnalysisUsage(AnalysisUsage &AU) const {
220   AU.setPreservesAll();
221 }
222 
223 char PhiValuesWrapperPass::ID = 0;
224 
225 INITIALIZE_PASS(PhiValuesWrapperPass, "phi-values", "Phi Values Analysis", false,
226                 true)
227