1 //===- LowerAllocations.cpp - Reduce malloc & free insts to calls ---------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // The LowerAllocations transformation is a target-dependent tranformation
11 // because it depends on the size of data types and alignment constraints.
13 //===----------------------------------------------------------------------===//
15 #define DEBUG_TYPE "lowerallocs"
16 #include "llvm/Transforms/Scalar.h"
17 #include "llvm/Transforms/Utils/UnifyFunctionExitNodes.h"
18 #include "llvm/Module.h"
19 #include "llvm/DerivedTypes.h"
20 #include "llvm/Instructions.h"
21 #include "llvm/Constants.h"
22 #include "llvm/LLVMContext.h"
23 #include "llvm/Pass.h"
24 #include "llvm/ADT/Statistic.h"
25 #include "llvm/Target/TargetData.h"
26 #include "llvm/Support/Compiler.h"
29 STATISTIC(NumLowered, "Number of allocations lowered");
32 /// LowerAllocations - Turn malloc and free instructions into %malloc and
35 class VISIBILITY_HIDDEN LowerAllocations : public BasicBlockPass {
36 Constant *MallocFunc; // Functions in the module we are processing
37 Constant *FreeFunc; // Initialized by doInitialization
38 bool LowerMallocArgToInteger;
40 static char ID; // Pass ID, replacement for typeid
41 explicit LowerAllocations(bool LowerToInt = false)
42 : BasicBlockPass(&ID), MallocFunc(0), FreeFunc(0),
43 LowerMallocArgToInteger(LowerToInt) {}
45 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
46 AU.addRequired<TargetData>();
49 // This is a cluster of orthogonal Transforms:
50 AU.addPreserved<UnifyFunctionExitNodes>();
51 AU.addPreservedID(PromoteMemoryToRegisterID);
52 AU.addPreservedID(LowerSwitchID);
53 AU.addPreservedID(LowerInvokePassID);
56 /// doPassInitialization - For the lower allocations pass, this ensures that
57 /// a module contains a declaration for a malloc and a free function.
59 bool doInitialization(Module &M);
61 virtual bool doInitialization(Function &F) {
62 return doInitialization(*F.getParent());
65 /// runOnBasicBlock - This method does the actual work of converting
66 /// instructions over, assuming that the pass has already been initialized.
68 bool runOnBasicBlock(BasicBlock &BB);
72 char LowerAllocations::ID = 0;
73 static RegisterPass<LowerAllocations>
74 X("lowerallocs", "Lower allocations from instructions to calls");
76 // Publically exposed interface to pass...
77 const PassInfo *const llvm::LowerAllocationsID = &X;
78 // createLowerAllocationsPass - Interface to this file...
79 Pass *llvm::createLowerAllocationsPass(bool LowerMallocArgToInteger) {
80 return new LowerAllocations(LowerMallocArgToInteger);
84 // doInitialization - For the lower allocations pass, this ensures that a
85 // module contains a declaration for a malloc and a free function.
87 // This function is always successful.
89 bool LowerAllocations::doInitialization(Module &M) {
90 // Ensure context initialization.
91 BasicBlockPass::doInitialization(M);
93 const Type *BPTy = Context->getPointerTypeUnqual(Type::Int8Ty);
94 // Prototype malloc as "char* malloc(...)", because we don't know in
95 // doInitialization whether size_t is int or long.
96 FunctionType *FT = Context->getFunctionType(BPTy, true);
97 MallocFunc = M.getOrInsertFunction("malloc", FT);
98 FreeFunc = M.getOrInsertFunction("free" , Type::VoidTy, BPTy, (Type *)0);
102 // runOnBasicBlock - This method does the actual work of converting
103 // instructions over, assuming that the pass has already been initialized.
105 bool LowerAllocations::runOnBasicBlock(BasicBlock &BB) {
106 bool Changed = false;
107 assert(MallocFunc && FreeFunc && "Pass not initialized!");
109 BasicBlock::InstListType &BBIL = BB.getInstList();
111 const TargetData &TD = getAnalysis<TargetData>();
112 const Type *IntPtrTy = TD.getIntPtrType();
114 // Loop over all of the instructions, looking for malloc or free instructions
115 for (BasicBlock::iterator I = BB.begin(), E = BB.end(); I != E; ++I) {
116 if (MallocInst *MI = dyn_cast<MallocInst>(I)) {
117 const Type *AllocTy = MI->getType()->getElementType();
119 // malloc(type) becomes i8 *malloc(size)
121 if (LowerMallocArgToInteger)
122 MallocArg = Context->getConstantInt(Type::Int64Ty,
123 TD.getTypeAllocSize(AllocTy));
125 MallocArg = Context->getConstantExprSizeOf(AllocTy);
127 Context->getConstantExprTruncOrBitCast(cast<Constant>(MallocArg),
130 if (MI->isArrayAllocation()) {
131 if (isa<ConstantInt>(MallocArg) &&
132 cast<ConstantInt>(MallocArg)->isOne()) {
133 MallocArg = MI->getOperand(0); // Operand * 1 = Operand
134 } else if (Constant *CO = dyn_cast<Constant>(MI->getOperand(0))) {
136 Context->getConstantExprIntegerCast(CO, IntPtrTy, false /*ZExt*/);
137 MallocArg = Context->getConstantExprMul(CO,
138 cast<Constant>(MallocArg));
140 Value *Scale = MI->getOperand(0);
141 if (Scale->getType() != IntPtrTy)
142 Scale = CastInst::CreateIntegerCast(Scale, IntPtrTy, false /*ZExt*/,
145 // Multiply it by the array size if necessary...
146 MallocArg = BinaryOperator::Create(Instruction::Mul, Scale,
151 // Create the call to Malloc.
152 CallInst *MCall = CallInst::Create(MallocFunc, MallocArg, "", I);
153 MCall->setTailCall();
155 // Create a cast instruction to convert to the right type...
157 if (MCall->getType() != Type::VoidTy)
158 MCast = new BitCastInst(MCall, MI->getType(), "", I);
160 MCast = Context->getNullValue(MI->getType());
162 // Replace all uses of the old malloc inst with the cast inst
163 MI->replaceAllUsesWith(MCast);
164 I = --BBIL.erase(I); // remove and delete the malloc instr...
167 } else if (FreeInst *FI = dyn_cast<FreeInst>(I)) {
169 new BitCastInst(FI->getOperand(0),
170 Context->getPointerTypeUnqual(Type::Int8Ty), "", I);
172 // Insert a call to the free function...
173 CallInst::Create(FreeFunc, PtrCast, "", I)->setTailCall();
175 // Delete the old free instruction