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/Intrinsics.h"
19 #include "llvm/IR/Module.h"
20 
21 using namespace llvm;
22 
23 // Search for virtual calls that call FPtr and add them to DevirtCalls.
24 static void
25 findCallsAtConstantOffset(SmallVectorImpl<DevirtCallSite> &DevirtCalls,
26                           bool *HasNonCallUses, Value *FPtr, uint64_t Offset,
27                           const CallInst *CI, DominatorTree &DT) {
28   for (const Use &U : FPtr->uses()) {
29     Instruction *User = cast<Instruction>(U.getUser());
30     // Ignore this instruction if it is not dominated by the type intrinsic
31     // being analyzed. Otherwise we may transform a call sharing the same
32     // vtable pointer incorrectly. Specifically, this situation can arise
33     // after indirect call promotion and inlining, where we may have uses
34     // of the vtable pointer guarded by a function pointer check, and a fallback
35     // indirect call.
36     if (!DT.dominates(CI, User))
37       continue;
38     if (isa<BitCastInst>(User)) {
39       findCallsAtConstantOffset(DevirtCalls, HasNonCallUses, User, Offset, CI,
40                                 DT);
41     } else if (auto *CI = dyn_cast<CallInst>(User)) {
42       DevirtCalls.push_back({Offset, *CI});
43     } else if (auto *II = dyn_cast<InvokeInst>(User)) {
44       DevirtCalls.push_back({Offset, *II});
45     } else if (HasNonCallUses) {
46       *HasNonCallUses = true;
47     }
48   }
49 }
50 
51 // Search for virtual calls that load from VPtr and add them to DevirtCalls.
52 static void findLoadCallsAtConstantOffset(
53     const Module *M, SmallVectorImpl<DevirtCallSite> &DevirtCalls, Value *VPtr,
54     int64_t Offset, const CallInst *CI, DominatorTree &DT) {
55   for (const Use &U : VPtr->uses()) {
56     Value *User = U.getUser();
57     if (isa<BitCastInst>(User)) {
58       findLoadCallsAtConstantOffset(M, DevirtCalls, User, Offset, CI, DT);
59     } else if (isa<LoadInst>(User)) {
60       findCallsAtConstantOffset(DevirtCalls, nullptr, User, Offset, CI, DT);
61     } else if (auto GEP = dyn_cast<GetElementPtrInst>(User)) {
62       // Take into account the GEP offset.
63       if (VPtr == GEP->getPointerOperand() && GEP->hasAllConstantIndices()) {
64         SmallVector<Value *, 8> Indices(GEP->op_begin() + 1, GEP->op_end());
65         int64_t GEPOffset = M->getDataLayout().getIndexedOffsetInType(
66             GEP->getSourceElementType(), Indices);
67         findLoadCallsAtConstantOffset(M, DevirtCalls, User, Offset + GEPOffset,
68                                       CI, DT);
69       }
70     }
71   }
72 }
73 
74 void llvm::findDevirtualizableCallsForTypeTest(
75     SmallVectorImpl<DevirtCallSite> &DevirtCalls,
76     SmallVectorImpl<CallInst *> &Assumes, const CallInst *CI,
77     DominatorTree &DT) {
78   assert(CI->getCalledFunction()->getIntrinsicID() == Intrinsic::type_test);
79 
80   const Module *M = CI->getParent()->getParent()->getParent();
81 
82   // Find llvm.assume intrinsics for this llvm.type.test call.
83   for (const Use &CIU : CI->uses()) {
84     if (auto *AssumeCI = dyn_cast<CallInst>(CIU.getUser())) {
85       Function *F = AssumeCI->getCalledFunction();
86       if (F && F->getIntrinsicID() == Intrinsic::assume)
87         Assumes.push_back(AssumeCI);
88     }
89   }
90 
91   // If we found any, search for virtual calls based on %p and add them to
92   // DevirtCalls.
93   if (!Assumes.empty())
94     findLoadCallsAtConstantOffset(
95         M, DevirtCalls, CI->getArgOperand(0)->stripPointerCasts(), 0, CI, DT);
96 }
97 
98 void llvm::findDevirtualizableCallsForTypeCheckedLoad(
99     SmallVectorImpl<DevirtCallSite> &DevirtCalls,
100     SmallVectorImpl<Instruction *> &LoadedPtrs,
101     SmallVectorImpl<Instruction *> &Preds, bool &HasNonCallUses,
102     const CallInst *CI, DominatorTree &DT) {
103   assert(CI->getCalledFunction()->getIntrinsicID() ==
104          Intrinsic::type_checked_load);
105 
106   auto *Offset = dyn_cast<ConstantInt>(CI->getArgOperand(1));
107   if (!Offset) {
108     HasNonCallUses = true;
109     return;
110   }
111 
112   for (const Use &U : CI->uses()) {
113     auto CIU = U.getUser();
114     if (auto EVI = dyn_cast<ExtractValueInst>(CIU)) {
115       if (EVI->getNumIndices() == 1 && EVI->getIndices()[0] == 0) {
116         LoadedPtrs.push_back(EVI);
117         continue;
118       }
119       if (EVI->getNumIndices() == 1 && EVI->getIndices()[0] == 1) {
120         Preds.push_back(EVI);
121         continue;
122       }
123     }
124     HasNonCallUses = true;
125   }
126 
127   for (Value *LoadedPtr : LoadedPtrs)
128     findCallsAtConstantOffset(DevirtCalls, &HasNonCallUses, LoadedPtr,
129                               Offset->getZExtValue(), CI, DT);
130 }
131 
132 Constant *llvm::getPointerAtOffset(Constant *I, uint64_t Offset, Module &M) {
133   if (I->getType()->isPointerTy()) {
134     if (Offset == 0)
135       return I;
136     return nullptr;
137   }
138 
139   const DataLayout &DL = M.getDataLayout();
140 
141   if (auto *C = dyn_cast<ConstantStruct>(I)) {
142     const StructLayout *SL = DL.getStructLayout(C->getType());
143     if (Offset >= SL->getSizeInBytes())
144       return nullptr;
145 
146     unsigned Op = SL->getElementContainingOffset(Offset);
147     return getPointerAtOffset(cast<Constant>(I->getOperand(Op)),
148                               Offset - SL->getElementOffset(Op), M);
149   }
150   if (auto *C = dyn_cast<ConstantArray>(I)) {
151     ArrayType *VTableTy = C->getType();
152     uint64_t ElemSize = DL.getTypeAllocSize(VTableTy->getElementType());
153 
154     unsigned Op = Offset / ElemSize;
155     if (Op >= C->getNumOperands())
156       return nullptr;
157 
158     return getPointerAtOffset(cast<Constant>(I->getOperand(Op)),
159                               Offset % ElemSize, M);
160   }
161   return nullptr;
162 }
163