| //===- llvm/Transforms/DecomposeMultiDimRefs.cpp - Lower array refs to 1D -===// |
| // |
| // DecomposeMultiDimRefs - Convert multi-dimensional references consisting of |
| // any combination of 2 or more array and structure indices into a sequence of |
| // instructions (using getelementpr and cast) so that each instruction has at |
| // most one index (except structure references, which need an extra leading |
| // index of [0]). |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #include "llvm/Transforms/Scalar.h" |
| #include "llvm/DerivedTypes.h" |
| #include "llvm/Constants.h" |
| #include "llvm/Constant.h" |
| #include "llvm/iMemory.h" |
| #include "llvm/iOther.h" |
| #include "llvm/BasicBlock.h" |
| #include "llvm/Pass.h" |
| #include "Support/StatisticReporter.h" |
| |
| namespace { |
| Statistic<> NumAdded("lowerrefs\t\t- # of getelementptr instructions added"); |
| |
| class DecomposePass : public BasicBlockPass { |
| static bool decomposeArrayRef(GetElementPtrInst &GEP); |
| public: |
| virtual bool runOnBasicBlock(BasicBlock &BB); |
| }; |
| |
| RegisterOpt<DecomposePass> X("lowerrefs", "Decompose multi-dimensional " |
| "structure/array references"); |
| } |
| |
| Pass |
| *createDecomposeMultiDimRefsPass() |
| { |
| return new DecomposePass(); |
| } |
| |
| |
| // runOnBasicBlock - Entry point for array or structure references with multiple |
| // indices. |
| // |
| bool |
| DecomposePass::runOnBasicBlock(BasicBlock &BB) |
| { |
| bool Changed = false; |
| for (BasicBlock::iterator II = BB.begin(); II != BB.end(); ) { |
| Instruction *I = II; |
| ++II; |
| if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(I)) |
| if (GEP->getNumIndices() >= 2) |
| Changed |= decomposeArrayRef(*GEP); // always modifies II |
| } |
| return Changed; |
| } |
| |
| // For any GetElementPtrInst with 2 or more array and structure indices: |
| // |
| // opCode CompositeType* P, [uint|ubyte] idx1, ..., [uint|ubyte] idxN |
| // |
| // this function generates the foll sequence: |
| // |
| // ptr1 = getElementPtr P, idx1 |
| // ptr2 = getElementPtr ptr1, 0, idx2 |
| // ... |
| // ptrN-1 = getElementPtr ptrN-2, 0, idxN-1 |
| // opCode ptrN-1, 0, idxN // New-MAI |
| // |
| // Then it replaces the original instruction with this sequence, |
| // and replaces all uses of the original instruction with New-MAI. |
| // If idx1 is 0, we simply omit the first getElementPtr instruction. |
| // |
| // On return: BBI points to the instruction after the current one |
| // (whether or not *BBI was replaced). |
| // |
| // Return value: true if the instruction was replaced; false otherwise. |
| // |
| bool |
| DecomposePass::decomposeArrayRef(GetElementPtrInst &GEP) |
| { |
| BasicBlock *BB = GEP.getParent(); |
| Value *LastPtr = GEP.getPointerOperand(); |
| Instruction *InsertPoint = GEP.getNext(); // Insert before the next insn |
| |
| // Process each index except the last one. |
| User::const_op_iterator OI = GEP.idx_begin(), OE = GEP.idx_end(); |
| for (; OI+1 != OE; ++OI) { |
| std::vector<Value*> Indices; |
| |
| // If this is the first index and is 0, skip it and move on! |
| if (OI == GEP.idx_begin()) { |
| if (*OI == ConstantInt::getNullValue((*OI)->getType())) |
| continue; |
| } else { |
| // Not the first index: include initial [0] to deref the last ptr |
| Indices.push_back(Constant::getNullValue(Type::LongTy)); |
| } |
| |
| Indices.push_back(*OI); |
| |
| // New Instruction: nextPtr1 = GetElementPtr LastPtr, Indices |
| LastPtr = new GetElementPtrInst(LastPtr, Indices, "ptr1", InsertPoint); |
| ++NumAdded; |
| } |
| |
| // Now create a new instruction to replace the original one |
| // |
| const PointerType *PtrTy = cast<PointerType>(LastPtr->getType()); |
| |
| // Get the final index vector, including an initial [0] as before. |
| std::vector<Value*> Indices; |
| Indices.push_back(Constant::getNullValue(Type::LongTy)); |
| Indices.push_back(*OI); |
| |
| Value *NewVal = new GetElementPtrInst(LastPtr, Indices, GEP.getName(), |
| InsertPoint); |
| |
| // Replace all uses of the old instruction with the new |
| GEP.replaceAllUsesWith(NewVal); |
| |
| // Now remove and delete the old instruction... |
| BB->getInstList().erase(&GEP); |
| return true; |
| } |