1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
|
//===- RelLookupTableConverterPass - Rel Table Conv -----------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// This file implements relative lookup table converter that converts
// lookup tables to relative lookup tables to make them PIC-friendly.
//
//===----------------------------------------------------------------------===//
#include "llvm/Transforms/Utils/RelLookupTableConverter.h"
#include "llvm/Analysis/ConstantFolding.h"
#include "llvm/Analysis/TargetTransformInfo.h"
#include "llvm/IR/BasicBlock.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/Module.h"
#include "llvm/InitializePasses.h"
#include "llvm/Pass.h"
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
using namespace llvm;
static bool shouldConvertToRelLookupTable(Module &M, GlobalVariable &GV) {
// If lookup table has more than one user,
// do not generate a relative lookup table.
// This is to simplify the analysis that needs to be done for this pass.
// TODO: Add support for lookup tables with multiple uses.
// For ex, this can happen when a function that uses a lookup table gets
// inlined into multiple call sites.
if (!GV.hasInitializer() ||
!GV.isConstant() ||
!GV.hasOneUse())
return false;
GetElementPtrInst *GEP =
dyn_cast<GetElementPtrInst>(GV.use_begin()->getUser());
if (!GEP || !GEP->hasOneUse())
return false;
LoadInst *Load = dyn_cast<LoadInst>(GEP->use_begin()->getUser());
if (!Load || !Load->hasOneUse())
return false;
// If the original lookup table does not have local linkage and is
// not dso_local, do not generate a relative lookup table.
// This optimization creates a relative lookup table that consists of
// offsets between the start of the lookup table and its elements.
// To be able to generate these offsets, relative lookup table and
// its elements should have internal linkage and be dso_local, which means
// that they should resolve to symbols within the same linkage unit.
if (!GV.hasLocalLinkage() ||
!GV.isDSOLocal() ||
!GV.isImplicitDSOLocal())
return false;
ConstantArray *Array = dyn_cast<ConstantArray>(GV.getInitializer());
// If values are not pointers, do not generate a relative lookup table.
if (!Array || !Array->getType()->getElementType()->isPointerTy())
return false;
const DataLayout &DL = M.getDataLayout();
for (const Use &Op : Array->operands()) {
Constant *ConstOp = cast<Constant>(&Op);
GlobalValue *GVOp;
APInt Offset;
// If an operand is not a constant offset from a lookup table,
// do not generate a relative lookup table.
if (!IsConstantOffsetFromGlobal(ConstOp, GVOp, Offset, DL))
return false;
// If operand is mutable, do not generate a relative lookup table.
auto *GlovalVarOp = dyn_cast<GlobalVariable>(GVOp);
if (!GlovalVarOp || !GlovalVarOp->isConstant())
return false;
if (!GlovalVarOp->hasLocalLinkage() ||
!GlovalVarOp->isDSOLocal() ||
!GlovalVarOp->isImplicitDSOLocal())
return false;
}
return true;
}
static GlobalVariable *createRelLookupTable(Function &Func,
GlobalVariable &LookupTable) {
Module &M = *Func.getParent();
ConstantArray *LookupTableArr =
cast<ConstantArray>(LookupTable.getInitializer());
unsigned NumElts = LookupTableArr->getType()->getNumElements();
ArrayType *IntArrayTy =
ArrayType::get(Type::getInt32Ty(M.getContext()), NumElts);
GlobalVariable *RelLookupTable = new GlobalVariable(
M, IntArrayTy, LookupTable.isConstant(), LookupTable.getLinkage(),
nullptr, "reltable." + Func.getName(), &LookupTable,
LookupTable.getThreadLocalMode(), LookupTable.getAddressSpace(),
LookupTable.isExternallyInitialized());
uint64_t Idx = 0;
SmallVector<Constant *, 64> RelLookupTableContents(NumElts);
for (Use &Operand : LookupTableArr->operands()) {
Constant *Element = cast<Constant>(Operand);
Type *IntPtrTy = M.getDataLayout().getIntPtrType(M.getContext());
Constant *Base = llvm::ConstantExpr::getPtrToInt(RelLookupTable, IntPtrTy);
Constant *Target = llvm::ConstantExpr::getPtrToInt(Element, IntPtrTy);
Constant *Sub = llvm::ConstantExpr::getSub(Target, Base);
Constant *RelOffset =
llvm::ConstantExpr::getTrunc(Sub, Type::getInt32Ty(M.getContext()));
RelLookupTableContents[Idx++] = RelOffset;
}
Constant *Initializer =
ConstantArray::get(IntArrayTy, RelLookupTableContents);
RelLookupTable->setInitializer(Initializer);
RelLookupTable->setUnnamedAddr(GlobalValue::UnnamedAddr::Global);
RelLookupTable->setAlignment(llvm::Align(4));
return RelLookupTable;
}
static void convertToRelLookupTable(GlobalVariable &LookupTable) {
GetElementPtrInst *GEP =
cast<GetElementPtrInst>(LookupTable.use_begin()->getUser());
LoadInst *Load = cast<LoadInst>(GEP->use_begin()->getUser());
Module &M = *LookupTable.getParent();
BasicBlock *BB = GEP->getParent();
IRBuilder<> Builder(BB);
Function &Func = *BB->getParent();
// Generate an array that consists of relative offsets.
GlobalVariable *RelLookupTable = createRelLookupTable(Func, LookupTable);
// Place new instruction sequence before GEP.
Builder.SetInsertPoint(GEP);
Value *Index = GEP->getOperand(2);
IntegerType *IntTy = cast<IntegerType>(Index->getType());
Value *Offset =
Builder.CreateShl(Index, ConstantInt::get(IntTy, 2), "reltable.shift");
Function *LoadRelIntrinsic = llvm::Intrinsic::getDeclaration(
&M, Intrinsic::load_relative, {Index->getType()});
Value *Base = Builder.CreateBitCast(RelLookupTable, Builder.getInt8PtrTy());
// Create a call to load.relative intrinsic that computes the target address
// by adding base address (lookup table address) and relative offset.
Value *Result = Builder.CreateCall(LoadRelIntrinsic, {Base, Offset},
"reltable.intrinsic");
// Create a bitcast instruction if necessary.
if (Load->getType() != Builder.getInt8PtrTy())
Result = Builder.CreateBitCast(Result, Load->getType(), "reltable.bitcast");
// Replace load instruction with the new generated instruction sequence.
Load->replaceAllUsesWith(Result);
// Remove Load and GEP instructions.
Load->eraseFromParent();
GEP->eraseFromParent();
}
// Convert lookup tables to relative lookup tables in the module.
static bool convertToRelativeLookupTables(
Module &M, function_ref<TargetTransformInfo &(Function &)> GetTTI) {
Module::iterator FI = M.begin();
if (FI == M.end())
return false;
// Check if we have a target that supports relative lookup tables.
if (!GetTTI(*FI).shouldBuildRelLookupTables())
return false;
bool Changed = false;
for (auto GVI = M.global_begin(), E = M.global_end(); GVI != E;) {
GlobalVariable &GV = *GVI++;
if (!shouldConvertToRelLookupTable(M, GV))
continue;
convertToRelLookupTable(GV);
// Remove the original lookup table.
GV.eraseFromParent();
Changed = true;
}
return Changed;
}
PreservedAnalyses RelLookupTableConverterPass::run(Module &M,
ModuleAnalysisManager &AM) {
FunctionAnalysisManager &FAM =
AM.getResult<FunctionAnalysisManagerModuleProxy>(M).getManager();
auto GetTTI = [&](Function &F) -> TargetTransformInfo & {
return FAM.getResult<TargetIRAnalysis>(F);
};
if (!convertToRelativeLookupTables(M, GetTTI))
return PreservedAnalyses::all();
PreservedAnalyses PA;
PA.preserveSet<CFGAnalyses>();
return PA;
}
|
