forked from OSchip/llvm-project
130 lines
4.1 KiB
C++
130 lines
4.1 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/Constants.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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namespace {
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Statistic<> NumAdded("lowerrefs\t\t- # of getelementptr instructions added");
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struct DecomposePass : public BasicBlockPass {
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virtual bool runOnBasicBlock(BasicBlock &BB);
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};
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}
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RegisterOpt<DecomposePass> X("lowerrefs", "Decompose multi-dimensional "
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"structure/array references");
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Pass
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*createDecomposeMultiDimRefsPass()
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{
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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
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DecomposePass::runOnBasicBlock(BasicBlock &BB)
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{
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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 (GetElementPtrInst *gep = dyn_cast<GetElementPtrInst>(&*II++)) // pre-inc
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if (gep->getNumIndices() >= 2)
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changed |= DecomposeArrayRef(gep); // always modifies II
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return changed;
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}
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// Function: DecomposeArrayRef()
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//
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// For any GetElementPtrInst with 2 or more array and structure indices:
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//
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// opCode CompositeType* P, [uint|ubyte] idx1, ..., [uint|ubyte] idxN
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//
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// this function generates the foll sequence:
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//
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// ptr1 = getElementPtr P, idx1
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// ptr2 = getElementPtr ptr1, 0, idx2
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// ...
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// ptrN-1 = getElementPtr ptrN-2, 0, idxN-1
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// opCode ptrN-1, 0, idxN // New-MAI
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//
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// Then it replaces the original instruction with this sequence,
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// and replaces all uses of the original instruction with New-MAI.
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// If idx1 is 0, we simply omit the first getElementPtr instruction.
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//
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// On return: BBI points to the instruction after the current one
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// (whether or not *BBI was replaced).
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//
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// Return value: true if the instruction was replaced; false otherwise.
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//
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bool
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DecomposeArrayRef(GetElementPtrInst* GEP)
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{
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if (GEP->getNumIndices() < 2)
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return false;
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BasicBlock *BB = GEP->getParent();
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Value *LastPtr = GEP->getPointerOperand();
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Instruction *InsertPoint = GEP->getNext(); // Insert before the next insn
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// The vector of new instructions to be created
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std::vector<Instruction*> NewInsts;
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// Process each index except the last one.
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User::const_op_iterator OI = GEP->idx_begin(), OE = GEP->idx_end();
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for (; OI+1 != OE; ++OI) {
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std::vector<Value*> Indices;
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// If this is the first index and is 0, skip it and move on!
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if (OI == GEP->idx_begin()) {
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if (*OI == ConstantInt::getNullValue((*OI)->getType()))
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continue;
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}
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else // Not the first index: include initial [0] to deref the last ptr
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Indices.push_back(Constant::getNullValue(Type::LongTy));
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Indices.push_back(*OI);
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// New Instruction: nextPtr1 = GetElementPtr LastPtr, Indices
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LastPtr = new GetElementPtrInst(LastPtr, Indices, "ptr1", InsertPoint);
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++NumAdded;
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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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const PointerType *PtrTy = cast<PointerType>(LastPtr->getType());
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// Get the final index vector, including an initial [0] as before.
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std::vector<Value*> Indices;
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Indices.push_back(Constant::getNullValue(Type::LongTy));
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Indices.push_back(*OI);
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Value *NewVal = new GetElementPtrInst(LastPtr, Indices, GEP->getName(),
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InsertPoint);
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// Replace all uses of the old instruction with the new
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GEP->replaceAllUsesWith(NewVal);
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// Now remove and delete the old instruction...
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BB->getInstList().erase(GEP);
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return true;
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}
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