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
findCallsAtConstantOffset(SmallVectorImpl<DevirtCallSite> & DevirtCalls,bool * HasNonCallUses,Value * FPtr,uint64_t Offset,const CallInst * CI,DominatorTree & DT)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.
findLoadCallsAtConstantOffset(const Module * M,SmallVectorImpl<DevirtCallSite> & DevirtCalls,Value * VPtr,int64_t Offset,const CallInst * CI,DominatorTree & DT)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
findDevirtualizableCallsForTypeTest(SmallVectorImpl<DevirtCallSite> & DevirtCalls,SmallVectorImpl<CallInst * > & Assumes,const CallInst * CI,DominatorTree & DT)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
findDevirtualizableCallsForTypeCheckedLoad(SmallVectorImpl<DevirtCallSite> & DevirtCalls,SmallVectorImpl<Instruction * > & LoadedPtrs,SmallVectorImpl<Instruction * > & Preds,bool & HasNonCallUses,const CallInst * CI,DominatorTree & DT)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
getPointerAtOffset(Constant * I,uint64_t Offset,Module & M,Constant * TopLevelGlobal)129 Constant *llvm::getPointerAtOffset(Constant *I, uint64_t Offset, Module &M,
130 Constant *TopLevelGlobal) {
131 if (I->getType()->isPointerTy()) {
132 if (Offset == 0)
133 return I;
134 return nullptr;
135 }
136
137 const DataLayout &DL = M.getDataLayout();
138
139 if (auto *C = dyn_cast<ConstantStruct>(I)) {
140 const StructLayout *SL = DL.getStructLayout(C->getType());
141 if (Offset >= SL->getSizeInBytes())
142 return nullptr;
143
144 unsigned Op = SL->getElementContainingOffset(Offset);
145 return getPointerAtOffset(cast<Constant>(I->getOperand(Op)),
146 Offset - SL->getElementOffset(Op), M,
147 TopLevelGlobal);
148 }
149 if (auto *C = dyn_cast<ConstantArray>(I)) {
150 ArrayType *VTableTy = C->getType();
151 uint64_t ElemSize = DL.getTypeAllocSize(VTableTy->getElementType());
152
153 unsigned Op = Offset / ElemSize;
154 if (Op >= C->getNumOperands())
155 return nullptr;
156
157 return getPointerAtOffset(cast<Constant>(I->getOperand(Op)),
158 Offset % ElemSize, M, TopLevelGlobal);
159 }
160
161 // (Swift-specific) relative-pointer support starts here.
162 if (auto *CI = dyn_cast<ConstantInt>(I)) {
163 if (Offset == 0 && CI->getZExtValue() == 0) {
164 return I;
165 }
166 }
167 if (auto *C = dyn_cast<ConstantExpr>(I)) {
168 switch (C->getOpcode()) {
169 case Instruction::Trunc:
170 case Instruction::PtrToInt:
171 return getPointerAtOffset(cast<Constant>(C->getOperand(0)), Offset, M,
172 TopLevelGlobal);
173 case Instruction::Sub: {
174 auto *Operand0 = cast<Constant>(C->getOperand(0));
175 auto *Operand1 = cast<Constant>(C->getOperand(1));
176
177 auto StripGEP = [](Constant *C) {
178 auto *CE = dyn_cast<ConstantExpr>(C);
179 if (!CE)
180 return C;
181 if (CE->getOpcode() != Instruction::GetElementPtr)
182 return C;
183 return CE->getOperand(0);
184 };
185 auto *Operand1TargetGlobal = StripGEP(getPointerAtOffset(Operand1, 0, M));
186
187 // Check that in the "sub (@a, @b)" expression, @b points back to the top
188 // level global (or a GEP thereof) that we're processing. Otherwise bail.
189 if (Operand1TargetGlobal != TopLevelGlobal)
190 return nullptr;
191
192 return getPointerAtOffset(Operand0, Offset, M, TopLevelGlobal);
193 }
194 default:
195 return nullptr;
196 }
197 }
198 return nullptr;
199 }
200
replaceRelativePointerUsersWithZero(Function * F)201 void llvm::replaceRelativePointerUsersWithZero(Function *F) {
202 for (auto *U : F->users()) {
203 auto *PtrExpr = dyn_cast<ConstantExpr>(U);
204 if (!PtrExpr || PtrExpr->getOpcode() != Instruction::PtrToInt)
205 continue;
206
207 for (auto *PtrToIntUser : PtrExpr->users()) {
208 auto *SubExpr = dyn_cast<ConstantExpr>(PtrToIntUser);
209 if (!SubExpr || SubExpr->getOpcode() != Instruction::Sub)
210 continue;
211
212 SubExpr->replaceNonMetadataUsesWith(
213 ConstantInt::get(SubExpr->getType(), 0));
214 }
215 }
216 }
217