1 //===- TypeMetadataUtils.cpp - Utilities related to type metadata ---------===//
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 functions that make it easier to manipulate type metadata
10 // for devirtualization.
11 //
12 //===----------------------------------------------------------------------===//
13 
14 #include "llvm/Analysis/TypeMetadataUtils.h"
15 #include "llvm/IR/Constants.h"
16 #include "llvm/IR/Dominators.h"
17 #include "llvm/IR/Instructions.h"
18 #include "llvm/IR/IntrinsicInst.h"
19 #include "llvm/IR/Intrinsics.h"
20 #include "llvm/IR/Module.h"
21 
22 using namespace llvm;
23 
24 // Search for virtual calls that call FPtr and add them to DevirtCalls.
25 static void
26 findCallsAtConstantOffset(SmallVectorImpl<DevirtCallSite> &DevirtCalls,
27                           bool *HasNonCallUses, Value *FPtr, uint64_t Offset,
28                           const CallInst *CI, DominatorTree &DT) {
29   for (const Use &U : FPtr->uses()) {
30     Instruction *User = cast<Instruction>(U.getUser());
31     // Ignore this instruction if it is not dominated by the type intrinsic
32     // being analyzed. Otherwise we may transform a call sharing the same
33     // vtable pointer incorrectly. Specifically, this situation can arise
34     // after indirect call promotion and inlining, where we may have uses
35     // of the vtable pointer guarded by a function pointer check, and a fallback
36     // indirect call.
37     if (!DT.dominates(CI, User))
38       continue;
39     if (isa<BitCastInst>(User)) {
40       findCallsAtConstantOffset(DevirtCalls, HasNonCallUses, User, Offset, CI,
41                                 DT);
42     } else if (auto *CI = dyn_cast<CallInst>(User)) {
43       DevirtCalls.push_back({Offset, *CI});
44     } else if (auto *II = dyn_cast<InvokeInst>(User)) {
45       DevirtCalls.push_back({Offset, *II});
46     } else if (HasNonCallUses) {
47       *HasNonCallUses = true;
48     }
49   }
50 }
51 
52 // Search for virtual calls that load from VPtr and add them to DevirtCalls.
53 static void findLoadCallsAtConstantOffset(
54     const Module *M, SmallVectorImpl<DevirtCallSite> &DevirtCalls, Value *VPtr,
55     int64_t Offset, const CallInst *CI, DominatorTree &DT) {
56   for (const Use &U : VPtr->uses()) {
57     Value *User = U.getUser();
58     if (isa<BitCastInst>(User)) {
59       findLoadCallsAtConstantOffset(M, DevirtCalls, User, Offset, CI, DT);
60     } else if (isa<LoadInst>(User)) {
61       findCallsAtConstantOffset(DevirtCalls, nullptr, User, Offset, CI, DT);
62     } else if (auto GEP = dyn_cast<GetElementPtrInst>(User)) {
63       // Take into account the GEP offset.
64       if (VPtr == GEP->getPointerOperand() && GEP->hasAllConstantIndices()) {
65         SmallVector<Value *, 8> Indices(GEP->op_begin() + 1, GEP->op_end());
66         int64_t GEPOffset = M->getDataLayout().getIndexedOffsetInType(
67             GEP->getSourceElementType(), Indices);
68         findLoadCallsAtConstantOffset(M, DevirtCalls, User, Offset + GEPOffset,
69                                       CI, DT);
70       }
71     }
72   }
73 }
74 
75 void llvm::findDevirtualizableCallsForTypeTest(
76     SmallVectorImpl<DevirtCallSite> &DevirtCalls,
77     SmallVectorImpl<CallInst *> &Assumes, const CallInst *CI,
78     DominatorTree &DT) {
79   assert(CI->getCalledFunction()->getIntrinsicID() == Intrinsic::type_test);
80 
81   const Module *M = CI->getParent()->getParent()->getParent();
82 
83   // Find llvm.assume intrinsics for this llvm.type.test call.
84   for (const Use &CIU : CI->uses())
85     if (auto *Assume = dyn_cast<AssumeInst>(CIU.getUser()))
86       Assumes.push_back(Assume);
87 
88   // If we found any, search for virtual calls based on %p and add them to
89   // DevirtCalls.
90   if (!Assumes.empty())
91     findLoadCallsAtConstantOffset(
92         M, DevirtCalls, CI->getArgOperand(0)->stripPointerCasts(), 0, CI, DT);
93 }
94 
95 void llvm::findDevirtualizableCallsForTypeCheckedLoad(
96     SmallVectorImpl<DevirtCallSite> &DevirtCalls,
97     SmallVectorImpl<Instruction *> &LoadedPtrs,
98     SmallVectorImpl<Instruction *> &Preds, bool &HasNonCallUses,
99     const CallInst *CI, DominatorTree &DT) {
100   assert(CI->getCalledFunction()->getIntrinsicID() ==
101          Intrinsic::type_checked_load);
102 
103   auto *Offset = dyn_cast<ConstantInt>(CI->getArgOperand(1));
104   if (!Offset) {
105     HasNonCallUses = true;
106     return;
107   }
108 
109   for (const Use &U : CI->uses()) {
110     auto CIU = U.getUser();
111     if (auto EVI = dyn_cast<ExtractValueInst>(CIU)) {
112       if (EVI->getNumIndices() == 1 && EVI->getIndices()[0] == 0) {
113         LoadedPtrs.push_back(EVI);
114         continue;
115       }
116       if (EVI->getNumIndices() == 1 && EVI->getIndices()[0] == 1) {
117         Preds.push_back(EVI);
118         continue;
119       }
120     }
121     HasNonCallUses = true;
122   }
123 
124   for (Value *LoadedPtr : LoadedPtrs)
125     findCallsAtConstantOffset(DevirtCalls, &HasNonCallUses, LoadedPtr,
126                               Offset->getZExtValue(), CI, DT);
127 }
128 
129 Constant *llvm::getPointerAtOffset(Constant *I, uint64_t Offset, Module &M) {
130   if (I->getType()->isPointerTy()) {
131     if (Offset == 0)
132       return I;
133     return nullptr;
134   }
135 
136   const DataLayout &DL = M.getDataLayout();
137 
138   if (auto *C = dyn_cast<ConstantStruct>(I)) {
139     const StructLayout *SL = DL.getStructLayout(C->getType());
140     if (Offset >= SL->getSizeInBytes())
141       return nullptr;
142 
143     unsigned Op = SL->getElementContainingOffset(Offset);
144     return getPointerAtOffset(cast<Constant>(I->getOperand(Op)),
145                               Offset - SL->getElementOffset(Op), M);
146   }
147   if (auto *C = dyn_cast<ConstantArray>(I)) {
148     ArrayType *VTableTy = C->getType();
149     uint64_t ElemSize = DL.getTypeAllocSize(VTableTy->getElementType());
150 
151     unsigned Op = Offset / ElemSize;
152     if (Op >= C->getNumOperands())
153       return nullptr;
154 
155     return getPointerAtOffset(cast<Constant>(I->getOperand(Op)),
156                               Offset % ElemSize, M);
157   }
158   return nullptr;
159 }
160