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