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the command line git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@2601 91177308-0d34-0410-b5e6-96231b3b80d8
172 lines
5.7 KiB
C++
172 lines
5.7 KiB
C++
//===- llvm/Transforms/DecomposeMultiDimRefs.cpp - Lower array refs to 1D -===//
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//
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// DecomposeMultiDimRefs - Convert multi-dimensional references consisting of
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// any combination of 2 or more array and structure indices into a sequence of
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// instructions (using getelementpr and cast) so that each instruction has at
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// most one index (except structure references, which need an extra leading
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// index of [0]).
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Transforms/Scalar.h"
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#include "llvm/DerivedTypes.h"
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#include "llvm/Constant.h"
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#include "llvm/iMemory.h"
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#include "llvm/iOther.h"
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#include "llvm/BasicBlock.h"
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#include "llvm/Pass.h"
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#include "Support/StatisticReporter.h"
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static Statistic<> NumAdded("lowerrefs\t\t- New instructions added");
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namespace {
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struct DecomposePass : public BasicBlockPass {
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const char *getPassName() const { return "Decompose Subscripting Exps"; }
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virtual bool runOnBasicBlock(BasicBlock *BB);
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private:
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static void decomposeArrayRef(BasicBlock::iterator &BBI);
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};
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}
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Pass *createDecomposeMultiDimRefsPass() {
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return new DecomposePass();
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}
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// runOnBasicBlock - Entry point for array or structure references with multiple
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// indices.
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//
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bool DecomposePass::runOnBasicBlock(BasicBlock *BB) {
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bool Changed = false;
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for (BasicBlock::iterator II = BB->begin(); II != BB->end(); ) {
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if (MemAccessInst *MAI = dyn_cast<MemAccessInst>(*II)) {
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if (MAI->getNumOperands() > MAI->getFirstIndexOperandNumber()+1) {
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decomposeArrayRef(II);
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Changed = true;
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} else {
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++II;
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}
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} else {
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++II;
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}
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}
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return Changed;
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}
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//
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// For any combination of 2 or more array and structure indices,
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// this function repeats the foll. until we have a one-dim. reference: {
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// ptr1 = getElementPtr [CompositeType-N] * lastPtr, uint firstIndex
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// ptr2 = cast [CompositeType-N] * ptr1 to [CompositeType-N] *
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// }
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// Then it replaces the original instruction with an equivalent one that
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// uses the last ptr2 generated in the loop and a single index.
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// If any index is (uint) 0, we omit the getElementPtr instruction.
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//
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void DecomposePass::decomposeArrayRef(BasicBlock::iterator &BBI) {
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MemAccessInst *MAI = cast<MemAccessInst>(*BBI);
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BasicBlock *BB = MAI->getParent();
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Value *LastPtr = MAI->getPointerOperand();
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// Remove the instruction from the stream
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BB->getInstList().remove(BBI);
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vector<Instruction*> NewInsts;
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// Process each index except the last one.
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//
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User::const_op_iterator OI = MAI->idx_begin(), OE = MAI->idx_end();
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for (; OI+1 != OE; ++OI) {
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assert(isa<PointerType>(LastPtr->getType()));
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// Check for a zero index. This will need a cast instead of
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// a getElementPtr, or it may need neither.
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bool indexIsZero = isa<Constant>(*OI) &&
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cast<Constant>(*OI)->isNullValue() &&
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(*OI)->getType() == Type::UIntTy;
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// Extract the first index. If the ptr is a pointer to a structure
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// and the next index is a structure offset (i.e., not an array offset),
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// we need to include an initial [0] to index into the pointer.
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//
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vector<Value*> Indices;
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PointerType *PtrTy = cast<PointerType>(LastPtr->getType());
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if (isa<StructType>(PtrTy->getElementType())
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&& !PtrTy->indexValid(*OI))
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Indices.push_back(Constant::getNullValue(Type::UIntTy));
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Indices.push_back(*OI);
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// Get the type obtained by applying the first index.
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// It must be a structure or array.
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const Type *NextTy = MemAccessInst::getIndexedType(LastPtr->getType(),
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Indices, true);
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assert(isa<CompositeType>(NextTy));
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// Get a pointer to the structure or to the elements of the array.
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const Type *NextPtrTy =
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PointerType::get(isa<StructType>(NextTy) ? NextTy
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: cast<ArrayType>(NextTy)->getElementType());
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// Instruction 1: nextPtr1 = GetElementPtr LastPtr, Indices
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// This is not needed if the index is zero.
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if (!indexIsZero) {
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LastPtr = new GetElementPtrInst(LastPtr, Indices, "ptr1");
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NewInsts.push_back(cast<Instruction>(LastPtr));
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++NumAdded;
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}
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// Instruction 2: nextPtr2 = cast nextPtr1 to NextPtrTy
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// This is not needed if the two types are identical.
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//
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if (LastPtr->getType() != NextPtrTy) {
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LastPtr = new CastInst(LastPtr, NextPtrTy, "ptr2");
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NewInsts.push_back(cast<Instruction>(LastPtr));
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++NumAdded;
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}
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}
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//
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// Now create a new instruction to replace the original one
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//
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PointerType *PtrTy = cast<PointerType>(LastPtr->getType());
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// First, get the final index vector. As above, we may need an initial [0].
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vector<Value*> Indices;
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if (isa<StructType>(PtrTy->getElementType())
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&& !PtrTy->indexValid(*OI))
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Indices.push_back(Constant::getNullValue(Type::UIntTy));
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Indices.push_back(*OI);
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Instruction *NewI = 0;
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switch(MAI->getOpcode()) {
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case Instruction::Load:
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NewI = new LoadInst(LastPtr, Indices, MAI->getName());
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break;
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case Instruction::Store:
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NewI = new StoreInst(MAI->getOperand(0), LastPtr, Indices);
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break;
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case Instruction::GetElementPtr:
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NewI = new GetElementPtrInst(LastPtr, Indices, MAI->getName());
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break;
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default:
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assert(0 && "Unrecognized memory access instruction");
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}
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NewInsts.push_back(NewI);
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// Replace all uses of the old instruction with the new
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MAI->replaceAllUsesWith(NewI);
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// Now delete the old instruction...
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delete MAI;
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// Insert all of the new instructions...
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BBI = BB->getInstList().insert(BBI, NewInsts.begin(), NewInsts.end());
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// Advance the iterator to the instruction following the one just inserted...
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BBI += NewInsts.size();
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}
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