1//===- llvm/Analysis/AssumptionCache.h - Track @llvm.assume -----*- 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// This file contains a pass that keeps track of @llvm.assume intrinsics in
10// the functions of a module (allowing assumptions within any function to be
11// found cheaply by other parts of the optimizer).
12//
13//===----------------------------------------------------------------------===//
14
15#ifndef LLVM_ANALYSIS_ASSUMPTIONCACHE_H
16#define LLVM_ANALYSIS_ASSUMPTIONCACHE_H
17
18#include "llvm/ADT/ArrayRef.h"
19#include "llvm/ADT/DenseMap.h"
20#include "llvm/ADT/DenseMapInfo.h"
21#include "llvm/ADT/SmallVector.h"
22#include "llvm/IR/PassManager.h"
23#include "llvm/IR/ValueHandle.h"
24#include "llvm/Pass.h"
25#include <memory>
26
27namespace llvm {
28
29class AssumeInst;
30class Function;
31class raw_ostream;
32class TargetTransformInfo;
33class Value;
34
35/// A cache of \@llvm.assume calls within a function.
36///
37/// This cache provides fast lookup of assumptions within a function by caching
38/// them and amortizing the cost of scanning for them across all queries. Passes
39/// that create new assumptions are required to call registerAssumption() to
40/// register any new \@llvm.assume calls that they create. Deletions of
41/// \@llvm.assume calls do not require special handling.
42class AssumptionCache {
43public:
44 /// Value of ResultElem::Index indicating that the argument to the call of the
45 /// llvm.assume.
46 enum : unsigned { ExprResultIdx = std::numeric_limits<unsigned>::max() };
47
48 struct ResultElem {
49 WeakVH Assume;
50
51 /// contains either ExprResultIdx or the index of the operand bundle
52 /// containing the knowledge.
53 unsigned Index;
54 operator Value *() const { return Assume; }
55 };
56
57private:
58 /// The function for which this cache is handling assumptions.
59 ///
60 /// We track this to lazily populate our assumptions.
61 Function &F;
62
63 TargetTransformInfo *TTI;
64
65 /// Vector of weak value handles to calls of the \@llvm.assume
66 /// intrinsic.
67 SmallVector<ResultElem, 4> AssumeHandles;
68
69 class AffectedValueCallbackVH final : public CallbackVH {
70 AssumptionCache *AC;
71
72 void deleted() override;
73 void allUsesReplacedWith(Value *) override;
74
75 public:
76 using DMI = DenseMapInfo<Value *>;
77
78 AffectedValueCallbackVH(Value *V, AssumptionCache *AC = nullptr)
79 : CallbackVH(V), AC(AC) {}
80 };
81
82 friend AffectedValueCallbackVH;
83
84 /// A map of values about which an assumption might be providing
85 /// information to the relevant set of assumptions.
86 using AffectedValuesMap =
87 DenseMap<AffectedValueCallbackVH, SmallVector<ResultElem, 1>,
88 AffectedValueCallbackVH::DMI>;
89 AffectedValuesMap AffectedValues;
90
91 /// Get the vector of assumptions which affect a value from the cache.
92 SmallVector<ResultElem, 1> &getOrInsertAffectedValues(Value *V);
93
94 /// Move affected values in the cache for OV to be affected values for NV.
95 void transferAffectedValuesInCache(Value *OV, Value *NV);
96
97 /// Flag tracking whether we have scanned the function yet.
98 ///
99 /// We want to be as lazy about this as possible, and so we scan the function
100 /// at the last moment.
101 bool Scanned = false;
102
103 /// Scan the function for assumptions and add them to the cache.
104 void scanFunction();
105
106public:
107 /// Construct an AssumptionCache from a function by scanning all of
108 /// its instructions.
109 AssumptionCache(Function &F, TargetTransformInfo *TTI = nullptr)
110 : F(F), TTI(TTI) {}
111
112 /// This cache is designed to be self-updating and so it should never be
113 /// invalidated.
114 bool invalidate(Function &, const PreservedAnalyses &,
115 FunctionAnalysisManager::Invalidator &) {
116 return false;
117 }
118
119 /// Add an \@llvm.assume intrinsic to this function's cache.
120 ///
121 /// The call passed in must be an instruction within this function and must
122 /// not already be in the cache.
123 void registerAssumption(AssumeInst *CI);
124
125 /// Remove an \@llvm.assume intrinsic from this function's cache if it has
126 /// been added to the cache earlier.
127 void unregisterAssumption(AssumeInst *CI);
128
129 /// Update the cache of values being affected by this assumption (i.e.
130 /// the values about which this assumption provides information).
131 void updateAffectedValues(AssumeInst *CI);
132
133 /// Clear the cache of \@llvm.assume intrinsics for a function.
134 ///
135 /// It will be re-scanned the next time it is requested.
136 void clear() {
137 AssumeHandles.clear();
138 AffectedValues.clear();
139 Scanned = false;
140 }
141
142 /// Access the list of assumption handles currently tracked for this
143 /// function.
144 ///
145 /// Note that these produce weak handles that may be null. The caller must
146 /// handle that case.
147 /// FIXME: We should replace this with pointee_iterator<filter_iterator<...>>
148 /// when we can write that to filter out the null values. Then caller code
149 /// will become simpler.
150 MutableArrayRef<ResultElem> assumptions() {
151 if (!Scanned)
152 scanFunction();
153 return AssumeHandles;
154 }
155
156 /// Access the list of assumptions which affect this value.
157 MutableArrayRef<ResultElem> assumptionsFor(const Value *V) {
158 if (!Scanned)
159 scanFunction();
160
161 auto AVI = AffectedValues.find_as(const_cast<Value *>(V));
162 if (AVI == AffectedValues.end())
163 return MutableArrayRef<ResultElem>();
164
165 return AVI->second;
166 }
167};
168
169/// A function analysis which provides an \c AssumptionCache.
170///
171/// This analysis is intended for use with the new pass manager and will vend
172/// assumption caches for a given function.
173class AssumptionAnalysis : public AnalysisInfoMixin<AssumptionAnalysis> {
174 friend AnalysisInfoMixin<AssumptionAnalysis>;
175
176 static AnalysisKey Key;
177
178public:
179 using Result = AssumptionCache;
180
181 AssumptionCache run(Function &F, FunctionAnalysisManager &);
182};
183
184/// Printer pass for the \c AssumptionAnalysis results.
185class AssumptionPrinterPass : public PassInfoMixin<AssumptionPrinterPass> {
186 raw_ostream &OS;
187
188public:
189 explicit AssumptionPrinterPass(raw_ostream &OS) : OS(OS) {}
190
191 PreservedAnalyses run(Function &F, FunctionAnalysisManager &AM);
192};
193
194/// An immutable pass that tracks lazily created \c AssumptionCache
195/// objects.
196///
197/// This is essentially a workaround for the legacy pass manager's weaknesses
198/// which associates each assumption cache with Function and clears it if the
199/// function is deleted. The nature of the AssumptionCache is that it is not
200/// invalidated by any changes to the function body and so this is sufficient
201/// to be conservatively correct.
202class AssumptionCacheTracker : public ImmutablePass {
203 /// A callback value handle applied to function objects, which we use to
204 /// delete our cache of intrinsics for a function when it is deleted.
205 class FunctionCallbackVH final : public CallbackVH {
206 AssumptionCacheTracker *ACT;
207
208 void deleted() override;
209
210 public:
211 using DMI = DenseMapInfo<Value *>;
212
213 FunctionCallbackVH(Value *V, AssumptionCacheTracker *ACT = nullptr)
214 : CallbackVH(V), ACT(ACT) {}
215 };
216
217 friend FunctionCallbackVH;
218
219 using FunctionCallsMap =
220 DenseMap<FunctionCallbackVH, std::unique_ptr<AssumptionCache>,
221 FunctionCallbackVH::DMI>;
222
223 FunctionCallsMap AssumptionCaches;
224
225public:
226 /// Get the cached assumptions for a function.
227 ///
228 /// If no assumptions are cached, this will scan the function. Otherwise, the
229 /// existing cache will be returned.
230 AssumptionCache &getAssumptionCache(Function &F);
231
232 /// Return the cached assumptions for a function if it has already been
233 /// scanned. Otherwise return nullptr.
234 AssumptionCache *lookupAssumptionCache(Function &F);
235
236 AssumptionCacheTracker();
237 ~AssumptionCacheTracker() override;
238
239 void releaseMemory() override {
240 verifyAnalysis();
241 AssumptionCaches.shrink_and_clear();
242 }
243
244 void verifyAnalysis() const override;
245
246 bool doFinalization(Module &) override {
247 verifyAnalysis();
248 return false;
249 }
250
251 static char ID; // Pass identification, replacement for typeid
252};
253
254template<> struct simplify_type<AssumptionCache::ResultElem> {
255 using SimpleType = Value *;
256
257 static SimpleType getSimplifiedValue(AssumptionCache::ResultElem &Val) {
258 return Val;
259 }
260};
261template<> struct simplify_type<const AssumptionCache::ResultElem> {
262 using SimpleType = /*const*/ Value *;
263
264 static SimpleType getSimplifiedValue(const AssumptionCache::ResultElem &Val) {
265 return Val;
266 }
267};
268
269} // end namespace llvm
270
271#endif // LLVM_ANALYSIS_ASSUMPTIONCACHE_H
272

source code of llvm/include/llvm/Analysis/AssumptionCache.h