1 //===- AssumptionCache.cpp - Cache finding @llvm.assume calls -------------===//
2 //
3 //                     The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // This file contains a pass that keeps track of @llvm.assume intrinsics in
11 // the functions of a module.
12 //
13 //===----------------------------------------------------------------------===//
14 
15 #include "llvm/Analysis/AssumptionCache.h"
16 #include "llvm/IR/CallSite.h"
17 #include "llvm/IR/Dominators.h"
18 #include "llvm/IR/Function.h"
19 #include "llvm/IR/Instructions.h"
20 #include "llvm/IR/IntrinsicInst.h"
21 #include "llvm/IR/PatternMatch.h"
22 #include "llvm/Support/Debug.h"
23 using namespace llvm;
24 using namespace llvm::PatternMatch;
25 
26 void AssumptionCache::scanFunction() {
27   assert(!Scanned && "Tried to scan the function twice!");
28   assert(AssumeHandles.empty() && "Already have assumes when scanning!");
29 
30   // Go through all instructions in all blocks, add all calls to @llvm.assume
31   // to this cache.
32   for (BasicBlock &B : F)
33     for (Instruction &II : B)
34       if (match(&II, m_Intrinsic<Intrinsic::assume>()))
35         AssumeHandles.push_back(&II);
36 
37   // Mark the scan as complete.
38   Scanned = true;
39 }
40 
41 void AssumptionCache::registerAssumption(CallInst *CI) {
42   assert(match(CI, m_Intrinsic<Intrinsic::assume>()) &&
43          "Registered call does not call @llvm.assume");
44 
45   // If we haven't scanned the function yet, just drop this assumption. It will
46   // be found when we scan later.
47   if (!Scanned)
48     return;
49 
50   AssumeHandles.push_back(CI);
51 
52 #ifndef NDEBUG
53   assert(CI->getParent() &&
54          "Cannot register @llvm.assume call not in a basic block");
55   assert(&F == CI->getParent()->getParent() &&
56          "Cannot register @llvm.assume call not in this function");
57 
58   // We expect the number of assumptions to be small, so in an asserts build
59   // check that we don't accumulate duplicates and that all assumptions point
60   // to the same function.
61   SmallPtrSet<Value *, 16> AssumptionSet;
62   for (auto &VH : AssumeHandles) {
63     if (!VH)
64       continue;
65 
66     assert(&F == cast<Instruction>(VH)->getParent()->getParent() &&
67            "Cached assumption not inside this function!");
68     assert(match(cast<CallInst>(VH), m_Intrinsic<Intrinsic::assume>()) &&
69            "Cached something other than a call to @llvm.assume!");
70     assert(AssumptionSet.insert(VH).second &&
71            "Cache contains multiple copies of a call!");
72   }
73 #endif
74 }
75 
76 void AssumptionCacheTracker::FunctionCallbackVH::deleted() {
77   auto I = ACT->AssumptionCaches.find_as(cast<Function>(getValPtr()));
78   if (I != ACT->AssumptionCaches.end())
79     ACT->AssumptionCaches.erase(I);
80   // 'this' now dangles!
81 }
82 
83 AssumptionCache &AssumptionCacheTracker::getAssumptionCache(Function &F) {
84   // We probe the function map twice to try and avoid creating a value handle
85   // around the function in common cases. This makes insertion a bit slower,
86   // but if we have to insert we're going to scan the whole function so that
87   // shouldn't matter.
88   auto I = AssumptionCaches.find_as(&F);
89   if (I != AssumptionCaches.end())
90     return *I->second;
91 
92   // Ok, build a new cache by scanning the function, insert it and the value
93   // handle into our map, and return the newly populated cache.
94   auto IP = AssumptionCaches.insert(std::make_pair(
95       FunctionCallbackVH(&F, this), llvm::make_unique<AssumptionCache>(F)));
96   assert(IP.second && "Scanning function already in the map?");
97   return *IP.first->second;
98 }
99 
100 void AssumptionCacheTracker::verifyAnalysis() const {
101 #ifndef NDEBUG
102   SmallPtrSet<const CallInst *, 4> AssumptionSet;
103   for (const auto &I : AssumptionCaches) {
104     for (auto &VH : I.second->assumptions())
105       if (VH)
106         AssumptionSet.insert(cast<CallInst>(VH));
107 
108     for (const BasicBlock &B : cast<Function>(*I.first))
109       for (const Instruction &II : B)
110         if (match(&II, m_Intrinsic<Intrinsic::assume>()))
111           assert(AssumptionSet.count(cast<CallInst>(&II)) &&
112                  "Assumption in scanned function not in cache");
113   }
114 #endif
115 }
116 
117 AssumptionCacheTracker::AssumptionCacheTracker() : ImmutablePass(ID) {
118   initializeAssumptionCacheTrackerPass(*PassRegistry::getPassRegistry());
119 }
120 
121 AssumptionCacheTracker::~AssumptionCacheTracker() {}
122 
123 INITIALIZE_PASS(AssumptionCacheTracker, "assumption-cache-tracker",
124                 "Assumption Cache Tracker", false, true)
125 char AssumptionCacheTracker::ID = 0;
126