1 //===- LoopAnalysisManager.cpp - Loop analysis management -----------------===//
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/LoopAnalysisManager.h"
10 #include "llvm/Analysis/BasicAliasAnalysis.h"
11 #include "llvm/Analysis/GlobalsModRef.h"
12 #include "llvm/Analysis/LoopInfo.h"
13 #include "llvm/Analysis/MemorySSA.h"
14 #include "llvm/Analysis/ScalarEvolution.h"
15 #include "llvm/Analysis/ScalarEvolutionAliasAnalysis.h"
16 #include "llvm/IR/Dominators.h"
17 
18 using namespace llvm;
19 
20 namespace llvm {
21 // Explicit template instantiations and specialization definitions for core
22 // template typedefs.
23 template class AllAnalysesOn<Loop>;
24 template class AnalysisManager<Loop, LoopStandardAnalysisResults &>;
25 template class InnerAnalysisManagerProxy<LoopAnalysisManager, Function>;
26 template class OuterAnalysisManagerProxy<FunctionAnalysisManager, Loop,
27                                          LoopStandardAnalysisResults &>;
28 
29 bool LoopAnalysisManagerFunctionProxy::Result::invalidate(
30     Function &F, const PreservedAnalyses &PA,
31     FunctionAnalysisManager::Invalidator &Inv) {
32   // First compute the sequence of IR units covered by this proxy. We will want
33   // to visit this in postorder, but because this is a tree structure we can do
34   // this by building a preorder sequence and walking it backwards. We also
35   // want siblings in forward program order to match the LoopPassManager so we
36   // get the preorder with siblings reversed.
37   SmallVector<Loop *, 4> PreOrderLoops = LI->getLoopsInReverseSiblingPreorder();
38 
39   // If this proxy or the loop info is going to be invalidated, we also need
40   // to clear all the keys coming from that analysis. We also completely blow
41   // away the loop analyses if any of the standard analyses provided by the
42   // loop pass manager go away so that loop analyses can freely use these
43   // without worrying about declaring dependencies on them etc.
44   // FIXME: It isn't clear if this is the right tradeoff. We could instead make
45   // loop analyses declare any dependencies on these and use the more general
46   // invalidation logic below to act on that.
47   auto PAC = PA.getChecker<LoopAnalysisManagerFunctionProxy>();
48   bool invalidateMemorySSAAnalysis = false;
49   if (MSSAUsed)
50     invalidateMemorySSAAnalysis = Inv.invalidate<MemorySSAAnalysis>(F, PA);
51   if (!(PAC.preserved() || PAC.preservedSet<AllAnalysesOn<Function>>()) ||
52       Inv.invalidate<AAManager>(F, PA) ||
53       Inv.invalidate<AssumptionAnalysis>(F, PA) ||
54       Inv.invalidate<DominatorTreeAnalysis>(F, PA) ||
55       Inv.invalidate<LoopAnalysis>(F, PA) ||
56       Inv.invalidate<ScalarEvolutionAnalysis>(F, PA) ||
57       invalidateMemorySSAAnalysis) {
58     // Note that the LoopInfo may be stale at this point, however the loop
59     // objects themselves remain the only viable keys that could be in the
60     // analysis manager's cache. So we just walk the keys and forcibly clear
61     // those results. Note that the order doesn't matter here as this will just
62     // directly destroy the results without calling methods on them.
63     for (Loop *L : PreOrderLoops) {
64       // NB! `L` may not be in a good enough state to run Loop::getName.
65       InnerAM->clear(*L, "<possibly invalidated loop>");
66     }
67 
68     // We also need to null out the inner AM so that when the object gets
69     // destroyed as invalid we don't try to clear the inner AM again. At that
70     // point we won't be able to reliably walk the loops for this function and
71     // only clear results associated with those loops the way we do here.
72     // FIXME: Making InnerAM null at this point isn't very nice. Most analyses
73     // try to remain valid during invalidation. Maybe we should add an
74     // `IsClean` flag?
75     InnerAM = nullptr;
76 
77     // Now return true to indicate this *is* invalid and a fresh proxy result
78     // needs to be built. This is especially important given the null InnerAM.
79     return true;
80   }
81 
82   // Directly check if the relevant set is preserved so we can short circuit
83   // invalidating loops.
84   bool AreLoopAnalysesPreserved =
85       PA.allAnalysesInSetPreserved<AllAnalysesOn<Loop>>();
86 
87   // Since we have a valid LoopInfo we can actually leave the cached results in
88   // the analysis manager associated with the Loop keys, but we need to
89   // propagate any necessary invalidation logic into them. We'd like to
90   // invalidate things in roughly the same order as they were put into the
91   // cache and so we walk the preorder list in reverse to form a valid
92   // postorder.
93   for (Loop *L : reverse(PreOrderLoops)) {
94     Optional<PreservedAnalyses> InnerPA;
95 
96     // Check to see whether the preserved set needs to be adjusted based on
97     // function-level analysis invalidation triggering deferred invalidation
98     // for this loop.
99     if (auto *OuterProxy =
100             InnerAM->getCachedResult<FunctionAnalysisManagerLoopProxy>(*L))
101       for (const auto &OuterInvalidationPair :
102            OuterProxy->getOuterInvalidations()) {
103         AnalysisKey *OuterAnalysisID = OuterInvalidationPair.first;
104         const auto &InnerAnalysisIDs = OuterInvalidationPair.second;
105         if (Inv.invalidate(OuterAnalysisID, F, PA)) {
106           if (!InnerPA)
107             InnerPA = PA;
108           for (AnalysisKey *InnerAnalysisID : InnerAnalysisIDs)
109             InnerPA->abandon(InnerAnalysisID);
110         }
111       }
112 
113     // Check if we needed a custom PA set. If so we'll need to run the inner
114     // invalidation.
115     if (InnerPA) {
116       InnerAM->invalidate(*L, *InnerPA);
117       continue;
118     }
119 
120     // Otherwise we only need to do invalidation if the original PA set didn't
121     // preserve all Loop analyses.
122     if (!AreLoopAnalysesPreserved)
123       InnerAM->invalidate(*L, PA);
124   }
125 
126   // Return false to indicate that this result is still a valid proxy.
127   return false;
128 }
129 
130 template <>
131 LoopAnalysisManagerFunctionProxy::Result
132 LoopAnalysisManagerFunctionProxy::run(Function &F,
133                                       FunctionAnalysisManager &AM) {
134   return Result(*InnerAM, AM.getResult<LoopAnalysis>(F));
135 }
136 }
137 
138 PreservedAnalyses llvm::getLoopPassPreservedAnalyses() {
139   PreservedAnalyses PA;
140   PA.preserve<DominatorTreeAnalysis>();
141   PA.preserve<LoopAnalysis>();
142   PA.preserve<LoopAnalysisManagerFunctionProxy>();
143   PA.preserve<ScalarEvolutionAnalysis>();
144   // FIXME: What we really want to do here is preserve an AA category, but that
145   // concept doesn't exist yet.
146   PA.preserve<AAManager>();
147   PA.preserve<BasicAA>();
148   PA.preserve<GlobalsAA>();
149   PA.preserve<SCEVAA>();
150   return PA;
151 }
152