1 /*
2 * Copyright 2016, The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17 #include "bcc/Config.h"
18 #include "Assert.h"
19 #include "Log.h"
20 #include "RSTransforms.h"
21
22 #include <cstdlib>
23
24 #include <llvm/IR/Function.h>
25 #include <llvm/IR/Instructions.h>
26 #include <llvm/IR/Module.h>
27 #include <llvm/Pass.h>
28 #include <llvm/IR/GetElementPtrTypeIterator.h>
29
30 namespace { // anonymous namespace
31
32 /* This pass translates GEPs that index into structs or arrays of structs to
33 * GEPs with an int8* operand and a byte offset. This translation is done to
34 * enforce on x86 the ARM alignment rule that 64-bit scalars be 8-byte aligned
35 * for structs with such scalars.
36 */
37 class RSX86TranslateGEPPass : public llvm::FunctionPass {
38 private:
39 static char ID;
40 llvm::LLVMContext *Context;
41 const llvm::DataLayout DL;
42
43 // Walk a GEP instruction and return true if any type indexed is a struct.
GEPIndexesStructType(const llvm::GetElementPtrInst * GEP)44 bool GEPIndexesStructType(const llvm::GetElementPtrInst *GEP) {
45 for (llvm::gep_type_iterator GTI = gep_type_begin(GEP),
46 GTE = gep_type_end(GEP);
47 GTI != GTE; ++GTI) {
48 if (llvm::dyn_cast<llvm::StructType>(*GTI)) {
49 return true;
50 }
51 }
52 return false;
53 }
54
55 // Helper method to add two llvm::Value parameters
incrementOffset(llvm::Value * accum,llvm::Value * incr,llvm::Instruction * InsertBefore)56 llvm::Value *incrementOffset(llvm::Value *accum, llvm::Value *incr,
57 llvm::Instruction *InsertBefore) {
58 if (accum == nullptr)
59 return incr;
60 return llvm::BinaryOperator::CreateAdd(accum, incr, "", InsertBefore);
61 }
62
63 // Compute the byte offset for a GEP from the GEP's base pointer operand.
64 // Based on visitGetElementPtrInst in llvm/lib/Transforms/Scalar/SROA.cpp.
65 // The difference is that this function handles non-constant array indices and
66 // constructs a sequence of instructions to calculate the offset. These
67 // instructions might not be the most efficient way to calculate this offset,
68 // but we rely on subsequent optimizations to do necessary fold/combine.
computeGEPOffset(llvm::GetElementPtrInst * GEP)69 llvm::Value *computeGEPOffset(llvm::GetElementPtrInst *GEP) {
70 llvm::Value *Offset = nullptr;
71
72 for (llvm::gep_type_iterator GTI = gep_type_begin(GEP),
73 GTE = gep_type_end(GEP);
74 GTI != GTE; ++GTI) {
75 if (llvm::StructType *STy = llvm::dyn_cast<llvm::StructType>(*GTI)) {
76 llvm::ConstantInt *OpC = llvm::dyn_cast<llvm::ConstantInt>(GTI.getOperand());
77 if (!OpC) {
78 ALOGE("Operand for struct type is not constant!");
79 bccAssert(false);
80 return nullptr; // NOLINT, unreached
81 }
82
83 // Offset = Offset + EltOffset for index into a struct
84 const llvm::StructLayout *SL = DL.getStructLayout(STy);
85 unsigned EltOffset = SL->getElementOffset(OpC->getZExtValue());
86 llvm::Value *Incr = llvm::ConstantInt::get(
87 llvm::Type::getInt32Ty(*Context), EltOffset);
88 Offset = incrementOffset(Offset, Incr, GEP);
89 } else {
90 // Offset = Offset + Index * EltSize for index into an array or a vector
91 llvm::Value *EltSize = llvm::ConstantInt::get(
92 llvm::Type::getInt32Ty(*Context),
93 DL.getTypeAllocSize(GTI.getIndexedType()));
94 llvm::Value *Incr = llvm::BinaryOperator::CreateMul(
95 GTI.getOperand() /* Index */,
96 EltSize, "", GEP);
97 Offset = incrementOffset(Offset, Incr, GEP);
98 }
99 }
100
101 return Offset;
102 }
103
translateGEP(llvm::GetElementPtrInst * GEP)104 void translateGEP(llvm::GetElementPtrInst *GEP) {
105 // cast GEP pointer operand to int8*
106 llvm::CastInst *Int8Ptr = llvm::CastInst::CreatePointerCast(
107 GEP->getPointerOperand(),
108 llvm::Type::getInt8PtrTy(*Context),
109 "to.int8ptr",
110 GEP);
111 llvm::Value *Indices[1] = {computeGEPOffset(GEP)};
112
113 // index into the int8* based on the byte offset
114 llvm::GetElementPtrInst *Int8PtrGEP = llvm::GetElementPtrInst::Create(
115 llvm::Type::getInt8Ty(*Context), Int8Ptr, llvm::makeArrayRef(Indices),
116 "int8ptr.indexed", GEP);
117 Int8PtrGEP->setIsInBounds(GEP->isInBounds());
118
119 // cast the indexed int8* back to the type of the original GEP
120 llvm::CastInst *OutCast = llvm::CastInst::CreatePointerCast(
121 Int8PtrGEP, GEP->getType(), "to.orig.geptype", GEP);
122
123 GEP->replaceAllUsesWith(OutCast);
124 }
125
126 public:
RSX86TranslateGEPPass()127 RSX86TranslateGEPPass()
128 : FunctionPass (ID), DL(X86_CUSTOM_DL_STRING) {
129 }
130
getAnalysisUsage(llvm::AnalysisUsage & AU) const131 virtual void getAnalysisUsage(llvm::AnalysisUsage &AU) const override {
132 // This pass is run in isolation in a separate pass manager. So setting
133 // AnalysisUsage is unnecessary. Set just for completeness.
134 AU.setPreservesCFG();
135 }
136
runOnFunction(llvm::Function & F)137 virtual bool runOnFunction(llvm::Function &F) override {
138 bool changed = false;
139 Context = &F.getParent()->getContext();
140
141 // To avoid updating/deleting instructions while walking a BasicBlock's instructions,
142 // collect the GEPs that need to be translated and process them
143 // subsequently.
144 std::vector<llvm::GetElementPtrInst *> GEPsToHandle;
145
146 for (auto &BB: F) {
147 for (auto &I: BB) {
148 if (auto *GEP = llvm::dyn_cast<llvm::GetElementPtrInst>(&I)) {
149 if (GEPIndexesStructType(GEP)) {
150 GEPsToHandle.push_back(GEP);
151 }
152 }
153 }
154 }
155
156 for (auto *GEP: GEPsToHandle) {
157 // Translate GEPs and erase them
158 translateGEP(GEP);
159 changed = true;
160 GEP->eraseFromParent();
161 }
162
163 return changed;
164 }
165
getPassName() const166 virtual const char *getPassName() const override {
167 return "Translate GEPs on structs, intended for x86 target";
168 }
169 };
170
171 }
172
173 char RSX86TranslateGEPPass::ID = 0;
174
175 namespace bcc {
176
177 llvm::FunctionPass *
createRSX86TranslateGEPPass()178 createRSX86TranslateGEPPass() {
179 return new RSX86TranslateGEPPass();
180 }
181
182 }
183