1//===- AssumptionCache.cpp - Cache finding @llvm.assume calls -------------===//
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.
11//
12//===----------------------------------------------------------------------===//
13
14#include "llvm/Analysis/AssumptionCache.h"
15#include "llvm/ADT/STLExtras.h"
16#include "llvm/ADT/SmallPtrSet.h"
17#include "llvm/ADT/SmallVector.h"
18#include "llvm/IR/BasicBlock.h"
19#include "llvm/IR/Function.h"
20#include "llvm/IR/InstrTypes.h"
21#include "llvm/IR/Instruction.h"
22#include "llvm/IR/Instructions.h"
23#include "llvm/IR/Intrinsics.h"
24#include "llvm/IR/PassManager.h"
25#include "llvm/IR/PatternMatch.h"
26#include "llvm/InitializePasses.h"
27#include "llvm/Pass.h"
28#include "llvm/Support/Casting.h"
29#include "llvm/Support/CommandLine.h"
30#include "llvm/Support/ErrorHandling.h"
31#include "llvm/Support/raw_ostream.h"
32#include <algorithm>
33#include <cassert>
34#include <utility>
35
36using namespace llvm;
37using namespace llvm::PatternMatch;
38
39static cl::opt<bool>
40    VerifyAssumptionCache("verify-assumption-cache", cl::Hidden,
41                          cl::desc("Enable verification of assumption cache"),
42                          cl::init(false));
43
44SmallVector<WeakTrackingVH, 1> &
45AssumptionCache::getOrInsertAffectedValues(Value *V) {
46  // Try using find_as first to avoid creating extra value handles just for the
47  // purpose of doing the lookup.
48  auto AVI = AffectedValues.find_as(V);
49  if (AVI != AffectedValues.end())
50    return AVI->second;
51
52  auto AVIP = AffectedValues.insert(
53      {AffectedValueCallbackVH(V, this), SmallVector<WeakTrackingVH, 1>()});
54  return AVIP.first->second;
55}
56
57static void findAffectedValues(CallInst *CI,
58                               SmallVectorImpl<Value *> &Affected) {
59  // Note: This code must be kept in-sync with the code in
60  // computeKnownBitsFromAssume in ValueTracking.
61
62  auto AddAffected = [&Affected](Value *V) {
63    if (isa<Argument>(V)) {
64      Affected.push_back(V);
65    } else if (auto *I = dyn_cast<Instruction>(V)) {
66      Affected.push_back(I);
67
68      // Peek through unary operators to find the source of the condition.
69      Value *Op;
70      if (match(I, m_BitCast(m_Value(Op))) ||
71          match(I, m_PtrToInt(m_Value(Op))) ||
72          match(I, m_Not(m_Value(Op)))) {
73        if (isa<Instruction>(Op) || isa<Argument>(Op))
74          Affected.push_back(Op);
75      }
76    }
77  };
78
79  Value *Cond = CI->getArgOperand(0), *A, *B;
80  AddAffected(Cond);
81
82  CmpInst::Predicate Pred;
83  if (match(Cond, m_ICmp(Pred, m_Value(A), m_Value(B)))) {
84    AddAffected(A);
85    AddAffected(B);
86
87    if (Pred == ICmpInst::ICMP_EQ) {
88      // For equality comparisons, we handle the case of bit inversion.
89      auto AddAffectedFromEq = [&AddAffected](Value *V) {
90        Value *A;
91        if (match(V, m_Not(m_Value(A)))) {
92          AddAffected(A);
93          V = A;
94        }
95
96        Value *B;
97        ConstantInt *C;
98        // (A & B) or (A | B) or (A ^ B).
99        if (match(V, m_BitwiseLogic(m_Value(A), m_Value(B)))) {
100          AddAffected(A);
101          AddAffected(B);
102        // (A << C) or (A >>_s C) or (A >>_u C) where C is some constant.
103        } else if (match(V, m_Shift(m_Value(A), m_ConstantInt(C)))) {
104          AddAffected(A);
105        }
106      };
107
108      AddAffectedFromEq(A);
109      AddAffectedFromEq(B);
110    }
111  }
112}
113
114void AssumptionCache::updateAffectedValues(CallInst *CI) {
115  SmallVector<Value *, 16> Affected;
116  findAffectedValues(CI, Affected);
117
118  for (auto &AV : Affected) {
119    auto &AVV = getOrInsertAffectedValues(AV);
120    if (std::find(AVV.begin(), AVV.end(), CI) == AVV.end())
121      AVV.push_back(CI);
122  }
123}
124
125void AssumptionCache::unregisterAssumption(CallInst *CI) {
126  SmallVector<Value *, 16> Affected;
127  findAffectedValues(CI, Affected);
128
129  for (auto &AV : Affected) {
130    auto AVI = AffectedValues.find_as(AV);
131    if (AVI != AffectedValues.end())
132      AffectedValues.erase(AVI);
133  }
134
135  AssumeHandles.erase(
136      remove_if(AssumeHandles, [CI](WeakTrackingVH &VH) { return CI == VH; }),
137      AssumeHandles.end());
138}
139
140void AssumptionCache::AffectedValueCallbackVH::deleted() {
141  auto AVI = AC->AffectedValues.find(getValPtr());
142  if (AVI != AC->AffectedValues.end())
143    AC->AffectedValues.erase(AVI);
144  // 'this' now dangles!
145}
146
147void AssumptionCache::transferAffectedValuesInCache(Value *OV, Value *NV) {
148  auto &NAVV = getOrInsertAffectedValues(NV);
149  auto AVI = AffectedValues.find(OV);
150  if (AVI == AffectedValues.end())
151    return;
152
153  for (auto &A : AVI->second)
154    if (std::find(NAVV.begin(), NAVV.end(), A) == NAVV.end())
155      NAVV.push_back(A);
156  AffectedValues.erase(OV);
157}
158
159void AssumptionCache::AffectedValueCallbackVH::allUsesReplacedWith(Value *NV) {
160  if (!isa<Instruction>(NV) && !isa<Argument>(NV))
161    return;
162
163  // Any assumptions that affected this value now affect the new value.
164
165  AC->transferAffectedValuesInCache(getValPtr(), NV);
166  // 'this' now might dangle! If the AffectedValues map was resized to add an
167  // entry for NV then this object might have been destroyed in favor of some
168  // copy in the grown map.
169}
170
171void AssumptionCache::scanFunction() {
172  assert(!Scanned && "Tried to scan the function twice!");
173  assert(AssumeHandles.empty() && "Already have assumes when scanning!");
174
175  // Go through all instructions in all blocks, add all calls to @llvm.assume
176  // to this cache.
177  for (BasicBlock &B : F)
178    for (Instruction &II : B)
179      if (match(&II, m_Intrinsic<Intrinsic::assume>()))
180        AssumeHandles.push_back(&II);
181
182  // Mark the scan as complete.
183  Scanned = true;
184
185  // Update affected values.
186  for (auto &A : AssumeHandles)
187    updateAffectedValues(cast<CallInst>(A));
188}
189
190void AssumptionCache::registerAssumption(CallInst *CI) {
191  assert(match(CI, m_Intrinsic<Intrinsic::assume>()) &&
192         "Registered call does not call @llvm.assume");
193
194  // If we haven't scanned the function yet, just drop this assumption. It will
195  // be found when we scan later.
196  if (!Scanned)
197    return;
198
199  AssumeHandles.push_back(CI);
200
201#ifndef NDEBUG
202  assert(CI->getParent() &&
203         "Cannot register @llvm.assume call not in a basic block");
204  assert(&F == CI->getParent()->getParent() &&
205         "Cannot register @llvm.assume call not in this function");
206
207  // We expect the number of assumptions to be small, so in an asserts build
208  // check that we don't accumulate duplicates and that all assumptions point
209  // to the same function.
210  SmallPtrSet<Value *, 16> AssumptionSet;
211  for (auto &VH : AssumeHandles) {
212    if (!VH)
213      continue;
214
215    assert(&F == cast<Instruction>(VH)->getParent()->getParent() &&
216           "Cached assumption not inside this function!");
217    assert(match(cast<CallInst>(VH), m_Intrinsic<Intrinsic::assume>()) &&
218           "Cached something other than a call to @llvm.assume!");
219    assert(AssumptionSet.insert(VH).second &&
220           "Cache contains multiple copies of a call!");
221  }
222#endif
223
224  updateAffectedValues(CI);
225}
226
227AnalysisKey AssumptionAnalysis::Key;
228
229PreservedAnalyses AssumptionPrinterPass::run(Function &F,
230                                             FunctionAnalysisManager &AM) {
231  AssumptionCache &AC = AM.getResult<AssumptionAnalysis>(F);
232
233  OS << "Cached assumptions for function: " << F.getName() << "\n";
234  for (auto &VH : AC.assumptions())
235    if (VH)
236      OS << "  " << *cast<CallInst>(VH)->getArgOperand(0) << "\n";
237
238  return PreservedAnalyses::all();
239}
240
241void AssumptionCacheTracker::FunctionCallbackVH::deleted() {
242  auto I = ACT->AssumptionCaches.find_as(cast<Function>(getValPtr()));
243  if (I != ACT->AssumptionCaches.end())
244    ACT->AssumptionCaches.erase(I);
245  // 'this' now dangles!
246}
247
248AssumptionCache &AssumptionCacheTracker::getAssumptionCache(Function &F) {
249  // We probe the function map twice to try and avoid creating a value handle
250  // around the function in common cases. This makes insertion a bit slower,
251  // but if we have to insert we're going to scan the whole function so that
252  // shouldn't matter.
253  auto I = AssumptionCaches.find_as(&F);
254  if (I != AssumptionCaches.end())
255    return *I->second;
256
257  // Ok, build a new cache by scanning the function, insert it and the value
258  // handle into our map, and return the newly populated cache.
259  auto IP = AssumptionCaches.insert(std::make_pair(
260      FunctionCallbackVH(&F, this), std::make_unique<AssumptionCache>(F)));
261  assert(IP.second && "Scanning function already in the map?");
262  return *IP.first->second;
263}
264
265AssumptionCache *AssumptionCacheTracker::lookupAssumptionCache(Function &F) {
266  auto I = AssumptionCaches.find_as(&F);
267  if (I != AssumptionCaches.end())
268    return I->second.get();
269  return nullptr;
270}
271
272void AssumptionCacheTracker::verifyAnalysis() const {
273  // FIXME: In the long term the verifier should not be controllable with a
274  // flag. We should either fix all passes to correctly update the assumption
275  // cache and enable the verifier unconditionally or somehow arrange for the
276  // assumption list to be updated automatically by passes.
277  if (!VerifyAssumptionCache)
278    return;
279
280  SmallPtrSet<const CallInst *, 4> AssumptionSet;
281  for (const auto &I : AssumptionCaches) {
282    for (auto &VH : I.second->assumptions())
283      if (VH)
284        AssumptionSet.insert(cast<CallInst>(VH));
285
286    for (const BasicBlock &B : cast<Function>(*I.first))
287      for (const Instruction &II : B)
288        if (match(&II, m_Intrinsic<Intrinsic::assume>()) &&
289            !AssumptionSet.count(cast<CallInst>(&II)))
290          report_fatal_error("Assumption in scanned function not in cache");
291  }
292}
293
294AssumptionCacheTracker::AssumptionCacheTracker() : ImmutablePass(ID) {
295  initializeAssumptionCacheTrackerPass(*PassRegistry::getPassRegistry());
296}
297
298AssumptionCacheTracker::~AssumptionCacheTracker() = default;
299
300char AssumptionCacheTracker::ID = 0;
301
302INITIALIZE_PASS(AssumptionCacheTracker, "assumption-cache-tracker",
303                "Assumption Cache Tracker", false, true)
304