LLVM API Documentation
00001 //===- llvm/Transforms/DecomposeMultiDimRefs.cpp - Lower array refs to 1D -===// 00002 // 00003 // The LLVM Compiler Infrastructure 00004 // 00005 // This file was developed by the LLVM research group and is distributed under 00006 // the University of Illinois Open Source License. See LICENSE.TXT for details. 00007 // 00008 //===----------------------------------------------------------------------===// 00009 // 00010 // DecomposeMultiDimRefs - Convert multi-dimensional references consisting of 00011 // any combination of 2 or more array and structure indices into a sequence of 00012 // instructions (using getelementpr and cast) so that each instruction has at 00013 // most one index (except structure references, which need an extra leading 00014 // index of [0]). 00015 // 00016 //===----------------------------------------------------------------------===// 00017 00018 #include "SparcV9Internals.h" 00019 #include "llvm/DerivedTypes.h" 00020 #include "llvm/Constants.h" 00021 #include "llvm/Constant.h" 00022 #include "llvm/Instructions.h" 00023 #include "llvm/BasicBlock.h" 00024 #include "llvm/Pass.h" 00025 #include "llvm/ADT/Statistic.h" 00026 #include "llvm/Support/Debug.h" 00027 using namespace llvm; 00028 00029 namespace { 00030 Statistic<> NumAdded("lowerrefs", "# of getelementptr instructions added"); 00031 00032 struct DecomposePass : public BasicBlockPass { 00033 virtual bool runOnBasicBlock(BasicBlock &BB); 00034 }; 00035 RegisterOpt<DecomposePass> X("lowerrefs", "Decompose multi-dimensional " 00036 "structure/array references"); 00037 } 00038 00039 // runOnBasicBlock - Entry point for array or structure references with multiple 00040 // indices. 00041 // 00042 bool DecomposePass::runOnBasicBlock(BasicBlock &BB) { 00043 bool changed = false; 00044 for (BasicBlock::iterator II = BB.begin(); II != BB.end(); ) 00045 if (GetElementPtrInst *gep = dyn_cast<GetElementPtrInst>(II++)) // pre-inc 00046 if (gep->getNumIndices() >= 2) 00047 changed |= DecomposeArrayRef(gep); // always modifies II 00048 return changed; 00049 } 00050 00051 FunctionPass *llvm::createDecomposeMultiDimRefsPass() { 00052 return new DecomposePass(); 00053 } 00054 00055 static inline bool isZeroConst (Value *V) { 00056 return isa<Constant> (V) && (cast<Constant>(V)->isNullValue()); 00057 } 00058 00059 // Function: DecomposeArrayRef() 00060 // 00061 // For any GetElementPtrInst with 2 or more array and structure indices: 00062 // 00063 // opCode CompositeType* P, [uint|ubyte] idx1, ..., [uint|ubyte] idxN 00064 // 00065 // this function generates the following sequence: 00066 // 00067 // ptr1 = getElementPtr P, idx1 00068 // ptr2 = getElementPtr ptr1, 0, idx2 00069 // ... 00070 // ptrN-1 = getElementPtr ptrN-2, 0, idxN-1 00071 // opCode ptrN-1, 0, idxN // New-MAI 00072 // 00073 // Then it replaces the original instruction with this sequence, 00074 // and replaces all uses of the original instruction with New-MAI. 00075 // If idx1 is 0, we simply omit the first getElementPtr instruction. 00076 // 00077 // On return: BBI points to the instruction after the current one 00078 // (whether or not *BBI was replaced). 00079 // 00080 // Return value: true if the instruction was replaced; false otherwise. 00081 // 00082 bool llvm::DecomposeArrayRef(GetElementPtrInst* GEP) { 00083 if (GEP->getNumIndices() < 2 00084 || (GEP->getNumIndices() == 2 00085 && isZeroConst(GEP->getOperand(1)))) { 00086 DEBUG (std::cerr << "DecomposeArrayRef: Skipping " << *GEP); 00087 return false; 00088 } else { 00089 DEBUG (std::cerr << "DecomposeArrayRef: Decomposing " << *GEP); 00090 } 00091 00092 BasicBlock *BB = GEP->getParent(); 00093 Value *LastPtr = GEP->getPointerOperand(); 00094 Instruction *InsertPoint = GEP->getNext(); // Insert before the next insn 00095 00096 // Process each index except the last one. 00097 User::const_op_iterator OI = GEP->idx_begin(), OE = GEP->idx_end(); 00098 for (; OI+1 != OE; ++OI) { 00099 std::vector<Value*> Indices; 00100 00101 // If this is the first index and is 0, skip it and move on! 00102 if (OI == GEP->idx_begin()) { 00103 if (isZeroConst (*OI)) 00104 continue; 00105 } 00106 else // Not the first index: include initial [0] to deref the last ptr 00107 Indices.push_back(Constant::getNullValue(Type::LongTy)); 00108 00109 Indices.push_back(*OI); 00110 00111 // New Instruction: nextPtr1 = GetElementPtr LastPtr, Indices 00112 LastPtr = new GetElementPtrInst(LastPtr, Indices, "ptr1", InsertPoint); 00113 ++NumAdded; 00114 } 00115 00116 // Now create a new instruction to replace the original one 00117 // 00118 const PointerType *PtrTy = cast<PointerType>(LastPtr->getType()); 00119 00120 // Get the final index vector, including an initial [0] as before. 00121 std::vector<Value*> Indices; 00122 Indices.push_back(Constant::getNullValue(Type::LongTy)); 00123 Indices.push_back(*OI); 00124 00125 Value *NewVal = new GetElementPtrInst(LastPtr, Indices, GEP->getName(), 00126 InsertPoint); 00127 00128 // Replace all uses of the old instruction with the new 00129 GEP->replaceAllUsesWith(NewVal); 00130 00131 // Now remove and delete the old instruction... 00132 BB->getInstList().erase(GEP); 00133 00134 return true; 00135 } 00136