xref: /freebsd/contrib/llvm-project/llvm/lib/Analysis/AssumptionCache.cpp (revision 833a452e9f082a7982a31c21f0da437dbbe0a39d)
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/AssumeBundleQueries.h"
15 #include "llvm/Analysis/AssumptionCache.h"
16 #include "llvm/ADT/STLExtras.h"
17 #include "llvm/ADT/SmallPtrSet.h"
18 #include "llvm/ADT/SmallVector.h"
19 #include "llvm/IR/BasicBlock.h"
20 #include "llvm/IR/Function.h"
21 #include "llvm/IR/InstrTypes.h"
22 #include "llvm/IR/Instruction.h"
23 #include "llvm/IR/Instructions.h"
24 #include "llvm/IR/Intrinsics.h"
25 #include "llvm/IR/PassManager.h"
26 #include "llvm/IR/PatternMatch.h"
27 #include "llvm/InitializePasses.h"
28 #include "llvm/Pass.h"
29 #include "llvm/Support/Casting.h"
30 #include "llvm/Support/CommandLine.h"
31 #include "llvm/Support/ErrorHandling.h"
32 #include "llvm/Support/raw_ostream.h"
33 #include <algorithm>
34 #include <cassert>
35 #include <utility>
36 
37 using namespace llvm;
38 using namespace llvm::PatternMatch;
39 
40 static cl::opt<bool>
41     VerifyAssumptionCache("verify-assumption-cache", cl::Hidden,
42                           cl::desc("Enable verification of assumption cache"),
43                           cl::init(false));
44 
45 SmallVector<AssumptionCache::ResultElem, 1> &
46 AssumptionCache::getOrInsertAffectedValues(Value *V) {
47   // Try using find_as first to avoid creating extra value handles just for the
48   // purpose of doing the lookup.
49   auto AVI = AffectedValues.find_as(V);
50   if (AVI != AffectedValues.end())
51     return AVI->second;
52 
53   auto AVIP = AffectedValues.insert(
54       {AffectedValueCallbackVH(V, this), SmallVector<ResultElem, 1>()});
55   return AVIP.first->second;
56 }
57 
58 static void
59 findAffectedValues(CallBase *CI,
60                    SmallVectorImpl<AssumptionCache::ResultElem> &Affected) {
61   // Note: This code must be kept in-sync with the code in
62   // computeKnownBitsFromAssume in ValueTracking.
63 
64   auto AddAffected = [&Affected](Value *V, unsigned Idx =
65                                                AssumptionCache::ExprResultIdx) {
66     if (isa<Argument>(V)) {
67       Affected.push_back({V, Idx});
68     } else if (auto *I = dyn_cast<Instruction>(V)) {
69       Affected.push_back({I, Idx});
70 
71       // Peek through unary operators to find the source of the condition.
72       Value *Op;
73       if (match(I, m_BitCast(m_Value(Op))) ||
74           match(I, m_PtrToInt(m_Value(Op))) || match(I, m_Not(m_Value(Op)))) {
75         if (isa<Instruction>(Op) || isa<Argument>(Op))
76           Affected.push_back({Op, Idx});
77       }
78     }
79   };
80 
81   for (unsigned Idx = 0; Idx != CI->getNumOperandBundles(); Idx++) {
82     if (CI->getOperandBundleAt(Idx).Inputs.size() > ABA_WasOn &&
83         CI->getOperandBundleAt(Idx).getTagName() != IgnoreBundleTag)
84       AddAffected(CI->getOperandBundleAt(Idx).Inputs[ABA_WasOn], Idx);
85   }
86 
87   Value *Cond = CI->getArgOperand(0), *A, *B;
88   AddAffected(Cond);
89 
90   CmpInst::Predicate Pred;
91   if (match(Cond, m_ICmp(Pred, m_Value(A), m_Value(B)))) {
92     AddAffected(A);
93     AddAffected(B);
94 
95     if (Pred == ICmpInst::ICMP_EQ) {
96       // For equality comparisons, we handle the case of bit inversion.
97       auto AddAffectedFromEq = [&AddAffected](Value *V) {
98         Value *A;
99         if (match(V, m_Not(m_Value(A)))) {
100           AddAffected(A);
101           V = A;
102         }
103 
104         Value *B;
105         // (A & B) or (A | B) or (A ^ B).
106         if (match(V, m_BitwiseLogic(m_Value(A), m_Value(B)))) {
107           AddAffected(A);
108           AddAffected(B);
109         // (A << C) or (A >>_s C) or (A >>_u C) where C is some constant.
110         } else if (match(V, m_Shift(m_Value(A), m_ConstantInt()))) {
111           AddAffected(A);
112         }
113       };
114 
115       AddAffectedFromEq(A);
116       AddAffectedFromEq(B);
117     }
118 
119     Value *X;
120     // Handle (A + C1) u< C2, which is the canonical form of A > C3 && A < C4,
121     // and recognized by LVI at least.
122     if (Pred == ICmpInst::ICMP_ULT &&
123         match(A, m_Add(m_Value(X), m_ConstantInt())) &&
124         match(B, m_ConstantInt()))
125       AddAffected(X);
126   }
127 }
128 
129 void AssumptionCache::updateAffectedValues(AssumeInst *CI) {
130   SmallVector<AssumptionCache::ResultElem, 16> Affected;
131   findAffectedValues(CI, Affected);
132 
133   for (auto &AV : Affected) {
134     auto &AVV = getOrInsertAffectedValues(AV.Assume);
135     if (std::find_if(AVV.begin(), AVV.end(), [&](ResultElem &Elem) {
136           return Elem.Assume == CI && Elem.Index == AV.Index;
137         }) == AVV.end())
138       AVV.push_back({CI, AV.Index});
139   }
140 }
141 
142 void AssumptionCache::unregisterAssumption(AssumeInst *CI) {
143   SmallVector<AssumptionCache::ResultElem, 16> Affected;
144   findAffectedValues(CI, Affected);
145 
146   for (auto &AV : Affected) {
147     auto AVI = AffectedValues.find_as(AV.Assume);
148     if (AVI == AffectedValues.end())
149       continue;
150     bool Found = false;
151     bool HasNonnull = false;
152     for (ResultElem &Elem : AVI->second) {
153       if (Elem.Assume == CI) {
154         Found = true;
155         Elem.Assume = nullptr;
156       }
157       HasNonnull |= !!Elem.Assume;
158       if (HasNonnull && Found)
159         break;
160     }
161     assert(Found && "already unregistered or incorrect cache state");
162     if (!HasNonnull)
163       AffectedValues.erase(AVI);
164   }
165 
166   erase_value(AssumeHandles, CI);
167 }
168 
169 void AssumptionCache::AffectedValueCallbackVH::deleted() {
170   AC->AffectedValues.erase(getValPtr());
171   // 'this' now dangles!
172 }
173 
174 void AssumptionCache::transferAffectedValuesInCache(Value *OV, Value *NV) {
175   auto &NAVV = getOrInsertAffectedValues(NV);
176   auto AVI = AffectedValues.find(OV);
177   if (AVI == AffectedValues.end())
178     return;
179 
180   for (auto &A : AVI->second)
181     if (!llvm::is_contained(NAVV, A))
182       NAVV.push_back(A);
183   AffectedValues.erase(OV);
184 }
185 
186 void AssumptionCache::AffectedValueCallbackVH::allUsesReplacedWith(Value *NV) {
187   if (!isa<Instruction>(NV) && !isa<Argument>(NV))
188     return;
189 
190   // Any assumptions that affected this value now affect the new value.
191 
192   AC->transferAffectedValuesInCache(getValPtr(), NV);
193   // 'this' now might dangle! If the AffectedValues map was resized to add an
194   // entry for NV then this object might have been destroyed in favor of some
195   // copy in the grown map.
196 }
197 
198 void AssumptionCache::scanFunction() {
199   assert(!Scanned && "Tried to scan the function twice!");
200   assert(AssumeHandles.empty() && "Already have assumes when scanning!");
201 
202   // Go through all instructions in all blocks, add all calls to @llvm.assume
203   // to this cache.
204   for (BasicBlock &B : F)
205     for (Instruction &I : B)
206       if (isa<AssumeInst>(&I))
207         AssumeHandles.push_back({&I, ExprResultIdx});
208 
209   // Mark the scan as complete.
210   Scanned = true;
211 
212   // Update affected values.
213   for (auto &A : AssumeHandles)
214     updateAffectedValues(cast<AssumeInst>(A));
215 }
216 
217 void AssumptionCache::registerAssumption(AssumeInst *CI) {
218   // If we haven't scanned the function yet, just drop this assumption. It will
219   // be found when we scan later.
220   if (!Scanned)
221     return;
222 
223   AssumeHandles.push_back({CI, ExprResultIdx});
224 
225 #ifndef NDEBUG
226   assert(CI->getParent() &&
227          "Cannot register @llvm.assume call not in a basic block");
228   assert(&F == CI->getParent()->getParent() &&
229          "Cannot register @llvm.assume call not in this function");
230 
231   // We expect the number of assumptions to be small, so in an asserts build
232   // check that we don't accumulate duplicates and that all assumptions point
233   // to the same function.
234   SmallPtrSet<Value *, 16> AssumptionSet;
235   for (auto &VH : AssumeHandles) {
236     if (!VH)
237       continue;
238 
239     assert(&F == cast<Instruction>(VH)->getParent()->getParent() &&
240            "Cached assumption not inside this function!");
241     assert(match(cast<CallInst>(VH), m_Intrinsic<Intrinsic::assume>()) &&
242            "Cached something other than a call to @llvm.assume!");
243     assert(AssumptionSet.insert(VH).second &&
244            "Cache contains multiple copies of a call!");
245   }
246 #endif
247 
248   updateAffectedValues(CI);
249 }
250 
251 AnalysisKey AssumptionAnalysis::Key;
252 
253 PreservedAnalyses AssumptionPrinterPass::run(Function &F,
254                                              FunctionAnalysisManager &AM) {
255   AssumptionCache &AC = AM.getResult<AssumptionAnalysis>(F);
256 
257   OS << "Cached assumptions for function: " << F.getName() << "\n";
258   for (auto &VH : AC.assumptions())
259     if (VH)
260       OS << "  " << *cast<CallInst>(VH)->getArgOperand(0) << "\n";
261 
262   return PreservedAnalyses::all();
263 }
264 
265 void AssumptionCacheTracker::FunctionCallbackVH::deleted() {
266   auto I = ACT->AssumptionCaches.find_as(cast<Function>(getValPtr()));
267   if (I != ACT->AssumptionCaches.end())
268     ACT->AssumptionCaches.erase(I);
269   // 'this' now dangles!
270 }
271 
272 AssumptionCache &AssumptionCacheTracker::getAssumptionCache(Function &F) {
273   // We probe the function map twice to try and avoid creating a value handle
274   // around the function in common cases. This makes insertion a bit slower,
275   // but if we have to insert we're going to scan the whole function so that
276   // shouldn't matter.
277   auto I = AssumptionCaches.find_as(&F);
278   if (I != AssumptionCaches.end())
279     return *I->second;
280 
281   // Ok, build a new cache by scanning the function, insert it and the value
282   // handle into our map, and return the newly populated cache.
283   auto IP = AssumptionCaches.insert(std::make_pair(
284       FunctionCallbackVH(&F, this), std::make_unique<AssumptionCache>(F)));
285   assert(IP.second && "Scanning function already in the map?");
286   return *IP.first->second;
287 }
288 
289 AssumptionCache *AssumptionCacheTracker::lookupAssumptionCache(Function &F) {
290   auto I = AssumptionCaches.find_as(&F);
291   if (I != AssumptionCaches.end())
292     return I->second.get();
293   return nullptr;
294 }
295 
296 void AssumptionCacheTracker::verifyAnalysis() const {
297   // FIXME: In the long term the verifier should not be controllable with a
298   // flag. We should either fix all passes to correctly update the assumption
299   // cache and enable the verifier unconditionally or somehow arrange for the
300   // assumption list to be updated automatically by passes.
301   if (!VerifyAssumptionCache)
302     return;
303 
304   SmallPtrSet<const CallInst *, 4> AssumptionSet;
305   for (const auto &I : AssumptionCaches) {
306     for (auto &VH : I.second->assumptions())
307       if (VH)
308         AssumptionSet.insert(cast<CallInst>(VH));
309 
310     for (const BasicBlock &B : cast<Function>(*I.first))
311       for (const Instruction &II : B)
312         if (match(&II, m_Intrinsic<Intrinsic::assume>()) &&
313             !AssumptionSet.count(cast<CallInst>(&II)))
314           report_fatal_error("Assumption in scanned function not in cache");
315   }
316 }
317 
318 AssumptionCacheTracker::AssumptionCacheTracker() : ImmutablePass(ID) {
319   initializeAssumptionCacheTrackerPass(*PassRegistry::getPassRegistry());
320 }
321 
322 AssumptionCacheTracker::~AssumptionCacheTracker() = default;
323 
324 char AssumptionCacheTracker::ID = 0;
325 
326 INITIALIZE_PASS(AssumptionCacheTracker, "assumption-cache-tracker",
327                 "Assumption Cache Tracker", false, true)
328