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//===- llvm/Transforms/DecomposeMultiDimRefs.cpp - Lower array refs to 1D -===//
//
// The LLVM Compiler Infrastructure
//
// This file was developed by the LLVM research group and is distributed under
// the University of Illinois Open Source License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// 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/Statistic.h"
using namespace llvm;
namespace {
Statistic<> NumAdded("lowerrefs", "# of getelementptr instructions added");
struct DecomposePass : public BasicBlockPass {
virtual bool runOnBasicBlock(BasicBlock &BB);
};
RegisterOpt<DecomposePass> X("lowerrefs", "Decompose multi-dimensional "
"structure/array references");
}
// 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 (GetElementPtrInst *gep = dyn_cast<GetElementPtrInst>(II++)) // pre-inc
if (gep->getNumIndices() >= 2)
changed |= DecomposeArrayRef(gep); // always modifies II
return changed;
}
FunctionPass *llvm::createDecomposeMultiDimRefsPass() {
return new DecomposePass();
}
// Function: DecomposeArrayRef()
//
// 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 llvm::DecomposeArrayRef(GetElementPtrInst* GEP) {
if (GEP->getNumIndices() < 2)
return false;
BasicBlock *BB = GEP->getParent();
Value *LastPtr = GEP->getPointerOperand();
Instruction *InsertPoint = GEP->getNext(); // Insert before the next insn
// The vector of new instructions to be created
std::vector<Instruction*> NewInsts;
// 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;
}
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